ICSE – Grade 9 – Chemistry – Ch 02 – QA

Questions & Answers

ICSE - Grade - 9

Subject: Chemistry

Chapter - 02 - Chemical Changes and Reactions

Types of Questions

MCQ

  1. What is a chemical change?
    A) Change in size
    B) Formation of a new substance
     C) Change in shape
     D) No new substance is formed
     Answer: B) Formation of a new substance


  2. Which of the following is not a chemical change?
    A) Burning of paper
    B) Rusting of iron
     C) Melting of ice
     D) Cooking of food
     Answer: C) Melting of ice


  3. Which of the following indicates a chemical reaction has occurred?
    A) Gas evolution
    B) Change in state
     C) Melting
     D) Breaking
     Answer: A) Gas evolution



  4. Which of the following is not a characteristic of chemical reaction?
    A) Evolution of gas
    B) Formation of precipitate
     C) Change in size
     D) Change in temperature
     Answer: C) Change in size



  5. Which of the following is a chemical reaction involving gas evolution?
    A) NaCl + AgNO₃
    B) Zn + H₂SO₄
     C) HCl + NaOH
     D) Fe + CuSO₄
     Answer: B) Zn + H₂SO₄



  6. The insoluble product formed in a chemical reaction is called:
    A) Solvent
    B) Gas
     C) Precipitate
     D) Mixture
     Answer: C) Precipitate



  7. In the reaction Fe + CuSO₄ → FeSO₄ + Cu, the change observed is:
    A) Change in temperature
    B) Formation of gas
     C) Change in colour
     D) Evolution of light
     Answer: C) Change in colour



  8. Which of the following is an exothermic reaction?
    A) CaCO₃ → CaO + CO₂
    B) Photosynthesis
     C) C + O₂ → CO₂
     D) Melting of ice
     Answer: C) C + O₂ → CO₂



  9. Which type of change is usually reversible?
    A) Physical change
    B) Chemical change
     C) Nuclear reaction
     D) Rusting
     Answer: A) Physical change



  10. In a physical change:
    A) New substances are formed
    B) Energy is always released
     C) No new substances are formed
     D) The substance cannot be reversed
     Answer: C) No new substances are formed



  11. Which of the following is a combination reaction?
    A) Zn + CuSO₄
    B) CaO + H₂O → Ca(OH)₂
     C) NaCl + AgNO₃
     D) HCl + NaOH
     Answer: B) CaO + H₂O → Ca(OH)₂



  12. What is the general form of a combination reaction?
    A) AB → A + B
    B) A + B → AB
     C) AB + CD → AD + CB
     D) AB + C → AC + B
     Answer: B) A + B → AB



  13. Identify the decomposition reaction:
    A) HCl + NaOH → NaCl + H₂O
    B) CaCO₃ → CaO + CO₂
     C) C + O₂ → CO₂
     D) Zn + CuSO₄ → ZnSO₄ + Cu
     Answer: B) CaCO₃ → CaO + CO₂



  14. What is the general form of a decomposition reaction?
    A) A + B → AB
    B) AB + C → AC + B
     C) AB → A + B
     D) AB + CD → AD + CB
     Answer: C) AB → A + B



  15. Which element can displace copper from copper sulphate solution?
    A) Silver
    B) Iron
     C) Gold
     D) Sodium
     Answer: B) Iron



  16. In a displacement reaction:
    A) A compound breaks into parts
    B) Two elements form a compound
     C) One element replaces another
     D) Ions are exchanged
     Answer: C) One element replaces another



  17. What is formed in a neutralisation reaction?
    A) Salt and acid
    B) Salt and water
     C) Water only
     D) Salt and base
     Answer: B) Salt and water



  18. Which of the following is a double displacement reaction?
    A) AgNO₃ + NaCl → AgCl + NaNO₃
    B) CaO + H₂O → Ca(OH)₂
     C) Fe + CuSO₄ → FeSO₄ + Cu
     D) C + O₂ → CO₂
     Answer: A) AgNO₃ + NaCl → AgCl + NaNO₃



  19. What happens in a double displacement reaction?
    A) Atoms are rearranged
    B) Ions are exchanged
     C) Metals are displaced
     D) Compounds decompose
     Answer: B) Ions are exchanged



  20. Which is an example of neutralisation reaction?
    A) H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O
    B) Fe + CuSO₄ → FeSO₄ + Cu
     C) CaCO₃ → CaO + CO₂
     D) C + O₂ → CO₂
     Answer: A) H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O



  21. The heat absorbed or released during a reaction is known as:
    A) Temperature
    B) Enthalpy
     C) Energy change
     D) Potential
     Answer: C) Energy change



  22. Photosynthesis is an example of:
    A) Decomposition reaction
    B) Exothermic reaction
     C) Endothermic reaction
     D) Displacement reaction
     Answer: C) Endothermic reaction



  23. Which reaction is endothermic?
    A) C + O₂ → CO₂
    B) Zn + H₂SO₄ → ZnSO₄ + H₂
     C) CaCO₃ → CaO + CO₂
     D) H₂ + Cl₂ → 2HCl
     Answer: C) CaCO₃ → CaO + CO₂



  24. Which of the following is not a type of chemical reaction?
    A) Combination
    B) Decomposition
     C) Sublimation
     D) Neutralisation
     Answer: C) Sublimation



  25. Rusting of iron involves:
    A) Oxygen and water
    B) Oxygen only
     C) Water only
     D) Nitrogen and hydrogen
     Answer: A) Oxygen and water



  26. Which product is formed during rusting?
    A) FeSO₄
    B) FeCl₃
     C) Fe₂O₃·xH₂O
     D) FeCO₃
     Answer: C) Fe₂O₃·xH₂O



  27. The gas evolved in the reaction: Zn + H₂SO₄ → ZnSO₄ + ?
    A) H₂
    B) O₂
     C) CO₂
     D) Cl₂
     Answer: A) H₂



  28. Burning of fuels is an example of:
    A) Endothermic reaction
    B) Physical change
     C) Exothermic reaction
     D) Neutralisation
     Answer: C) Exothermic reaction



  29. The chemical reaction CaO + H₂O → Ca(OH)₂ is a:
    A) Combination reaction
    B) Decomposition reaction
     C) Displacement reaction
     D) Neutralisation
     Answer: A) Combination reaction



  30. In a reaction, a white precipitate of BaSO₄ is formed. This indicates a:
    A) Displacement reaction
    B) Double displacement reaction
     C) Physical change
     D) Combination reaction
     Answer: B) Double displacement reaction



  31. Which change is reversible?
    A) Melting of ice
    B) Burning of paper
     C) Digestion of food
     D) Rusting of iron
     Answer: A) Melting of ice



  32. Which of the following always involves energy change?
    A) Physical change
    B) Chemical change
     C) Phase change
     D) Evaporation
     Answer: B) Chemical change



  33. A + B → AB is a:
    A) Combination reaction
    B) Displacement reaction
     C) Decomposition reaction
     D) Double displacement reaction
     Answer: A) Combination reaction



  34. AB → A + B is a:
    A) Combination reaction
    B) Decomposition reaction
     C) Neutralisation
     D) Displacement
     Answer: B) Decomposition reaction



  35. A + BC → AC + B is a:
    A) Double displacement
    B) Displacement
     C) Decomposition
     D) Combination
     Answer: B) Displacement



  36. AB + CD → AD + CB is a:
    A) Neutralisation
    B) Combination
     C) Double displacement
     D) Displacement
     Answer: C) Double displacement



  37. Which of these reactions is used to test presence of acid?
    A) HCl + Zn
    B) HCl + NaOH
     C) AgNO₃ + NaCl
     D) CaCO₃ → CaO + CO₂
     Answer: A) HCl + Zn



  38. Fe + CuSO₄ → FeSO₄ + Cu is what type of reaction?
    A) Combination
    B) Decomposition
     C) Displacement
     D) Neutralisation
     Answer: C) Displacement



  39. A student mixes BaCl₂ and Na₂SO₄. What will happen?
    A) Gas evolves
    B) Colour change
     C) White precipitate of BaSO₄
     D) No reaction
     Answer: C) White precipitate of BaSO₄



  40. Which chemical reaction requires sunlight?
    A) Photosynthesis
    B) Respiration
     C) Combustion
     D) Rusting
     Answer: A) Photosynthesis



  41. In neutralisation, the acid and base form:
    A) Gas and salt
    B) Salt and water
     C) Acid and gas
     D) Base and heat
     Answer: B) Salt and water



  42. When HCl reacts with NaOH, the salt formed is:
    A) Na₂SO₄
    B) NaCl
     C) KCl
     D) CaCl₂
     Answer: B) NaCl



  43. The decomposition of HgO forms:
    A) Hg and H₂
    B) Hg and O₂
     C) Hg and CO₂
     D) Hg only
     Answer: B) Hg and O₂



  44. Which reaction involves exchange of ions?
    A) Double displacement
    B) Decomposition
     C) Combination
     D) Displacement
     Answer: A) Double displacement



  45. 2HgO → 2Hg + O₂ is an example of:
    A) Displacement
    B) Combination
     C) Decomposition
     D) Double displacement
     Answer: C) Decomposition



  46. Which of these is used in photography and gives a white ppt on reacting with NaCl?
    A) CuSO₄
    B) FeSO₄
     C) AgNO₃
     D) ZnSO₄
     Answer: C) AgNO₃


  47. NaOH is a:
    A) Salt
    B) Acid
     C) Base
     D) Oxide
     Answer: C) Base



  48. H₂SO₄ is a:
    A) Salt
    B) Acid
     C) Base
     D) Metal
     Answer: B) Acid



  49. A reaction that absorbs heat from surroundings is:
    A) Exothermic
    B) Endothermic
     C) Neutralisation
     D) Combination
     Answer: B) Endothermic


  50. In rusting, the final product is:
    A) FeSO₄
    B) Fe₂O₃·xH₂O
     C) FeCO₃
     D) FeCl₃
     Answer: B) Fe₂O₃·xH₂O

Fill in the Blanks

  1. A __________ change results in the formation of one or more new substances.
     chemical


  2. Chemical changes are also called __________.
     chemical reactions


  3. A chemical change is usually __________.
     irreversible


  4. The formation of gas in a reaction is a sign of a __________ change.
     chemical


  5. In the reaction Zn + H₂SO₄ → ZnSO₄ + H₂, __________ gas is evolved.
     hydrogen


  6. An insoluble solid formed during a chemical reaction is called a __________.
     precipitate


  7. A noticeable change in __________ is one of the signs of a chemical reaction.
     colour


  8. Reactions that release heat are known as __________ reactions.
     exothermic


  9. Reactions that absorb heat are known as __________ reactions.
     endothermic


  10. A __________ change does not form any new substance.
     physical


  11. The rust formed on iron is chemically written as __________.
     Fe₂O₃·xH₂O


  12. In the reaction CaO + H₂O → Ca(OH)₂, the product formed is __________.
     calcium hydroxide


  13. The general form of a combination reaction is __________.
     A + B → AB


  14. The reaction 2HgO → 2Hg + O₂ is a __________ reaction.
     decomposition


  15. In displacement reactions, a __________ reactive element displaces a __________ reactive one.
     more, less


  16. Fe + CuSO₄ → FeSO₄ + Cu is a __________ reaction.
     displacement


  17. In a double displacement reaction, __________ are exchanged.
     ions


  18. The reaction between NaCl and AgNO₃ forms a __________ coloured precipitate of AgCl.
     white


  19. The general form of a double displacement reaction is __________.
     AB + CD → AD + CB


  20. In neutralisation reactions, an acid reacts with a base to form __________ and __________.
     salt, water


  21. The reaction HCl + NaOH → NaCl + H₂O is a __________ reaction.
     neutralisation


  22. Chemical changes always involve a change in __________.
     energy


  23. Photosynthesis is an example of an __________ chemical reaction.
     endothermic


  24. Burning of fuels is an example of an __________ chemical reaction.
     exothermic


  25. During photosynthesis, plants use __________ energy to prepare food.
     solar


  26. Chemical reactions are often indicated by evolution of gas, formation of __________, or change in colour.
     precipitate


  27. Decomposition reactions are often initiated by __________.
     heat


  28. A combination reaction involves the formation of a __________ product.
     single


  29. The reaction CaCO₃ → CaO + CO₂ is an example of a __________ reaction.
     decomposition


  30. The white solid formed in BaCl₂ + Na₂SO₄ is __________.
     BaSO₄


  31. Zn + CuSO₄ → ZnSO₄ + Cu is a reaction showing __________ of copper by zinc.
     displacement


  32. Double displacement reactions generally occur in __________ solution.
     aqueous


  33. The reaction C + O₂ → CO₂ + heat is __________ in nature.
     exothermic


  34. A reaction where heat is absorbed from the surroundings is called an __________ reaction.
     endothermic


  35. Fe₂O₃·xH₂O is commonly known as __________.
     rust


  36. Evolution of a gas, change in temperature, and change in colour are __________ of chemical reaction.
     characteristics


  37. A __________ is a solid formed from two aqueous solutions.
     precipitate


  38. The acid used in neutralisation reaction with NaOH to form NaCl is __________.
     HCl


  39. Neutralisation reactions help to reduce the effect of __________ and __________.
     acids, bases


  40. AgNO₃ + NaCl → AgCl + NaNO₃ is a __________ reaction.
     double displacement


  41. The colourless gas evolved in the reaction CaCO₃ → CaO + CO₂ is __________.
     carbon dioxide


  42. The product formed in H₂ + Cl₂ → 2HCl is __________.
     hydrogen chloride


  43. The physical change of ice melting into water is __________.
     reversible


  44. In photosynthesis, __________ dioxide is converted into glucose and oxygen.
     carbon


  45. The acid formed in the reaction of H₂ and Cl₂ is __________.
     hydrochloric acid


  46. The reaction where Zn replaces Cu from its salt solution is called a __________ reaction.
     displacement


  47. Double displacement reactions often result in formation of a __________ or gas.
     precipitate


  48. When a base neutralises an acid, the pH moves towards __________.
     7


  49. Reactions where compounds break down into simpler substances are called __________ reactions.
     decomposition


  50. Chemical changes are essential to biological and __________ processes.
     industrial

Name the Following

  1. Name the process in which new substances are formed with new properties.
     Chemical change


  2. Name the gas evolved when zinc reacts with dilute sulphuric acid.
     Hydrogen


  3. Name the solid formed in a reaction between BaCl₂ and Na₂SO₄.
     Barium sulphate


  4. Name the type of change that is usually reversible.
     Physical change


  5. Name the reaction in which two or more substances combine to form a single product.
     Combination reaction


  6. Name the reaction where a compound breaks into simpler substances.
     Decomposition reaction


  7. Name the reaction in which one element replaces another in a compound.
     Displacement reaction


  8. Name the reaction involving exchange of ions between two compounds.
     Double displacement reaction


  9. Name the reaction between an acid and a base to form salt and water.
     Neutralisation reaction


  10. Name the type of reaction in which heat is released.
     Exothermic reaction


  11. Name the type of reaction in which heat is absorbed.
     Endothermic reaction


  12. Name the chemical reaction involved in rusting of iron.
     Oxidation reaction


  13. Name the compound formed when iron rusts.
     Hydrated ferric oxide (Fe₂O₃·xH₂O)


  14. Name the white precipitate formed when AgNO₃ reacts with NaCl.
     Silver chloride (AgCl)


  15. Name the energy required for photosynthesis.
     Sunlight (solar energy)


  16. Name a chemical change that occurs in green plants.
     Photosynthesis


  17. Name a chemical change that occurs in our body to produce energy.
     Respiration


  18. Name a common acid used in neutralisation reactions.
     Hydrochloric acid (HCl)


  19. Name a common base used in neutralisation reactions.
     Sodium hydroxide (NaOH)


  20. Name the salt formed in the reaction between HCl and NaOH.
     Sodium chloride (NaCl)


  21. Name the gas evolved when calcium carbonate decomposes.
     Carbon dioxide (CO₂)


  22. Name the base formed in the reaction CaO + H₂O.
     Calcium hydroxide [Ca(OH)₂]


  23. Name a metal that displaces copper from copper sulphate solution.
     Zinc


  24. Name the brown metal deposited when Fe reacts with CuSO₄.
     Copper


  25. Name the gas formed in the decomposition of mercuric oxide.
     Oxygen


  26. Name the metal obtained when mercuric oxide is decomposed.
     Mercury


  27. Name the change involved when ice melts into water.
     Physical change


  28. Name the change involved when paper burns.
     Chemical change


  29. Name one product of combustion of carbon in air.
     Carbon dioxide


  30. Name a reaction used in industries to produce quick lime.
     Decomposition of calcium carbonate


  31. Name the chemical formula of rust.
     Fe₂O₃·xH₂O


  32. Name the colour of precipitate formed in AgNO₃ and NaCl reaction.
     White


  33. Name the metal more reactive than copper but less reactive than zinc.
     Iron


  34. Name the general reaction form of combination reactions.
     A + B → AB


  35. Name the general reaction form of decomposition reactions.
     AB → A + B


  36. Name the general reaction form of displacement reactions.
     A + BC → AC + B


  37. Name the general reaction form of double displacement reactions.
     AB + CD → AD + CB


  38. Name one natural example of an endothermic reaction.
     Photosynthesis


  39. Name one everyday example of an exothermic reaction.
     Burning of fuels


  40. Name a test to confirm evolution of hydrogen gas.
     Pop test


  41. Name the reaction where Fe reacts with CuSO₄ solution.
     Displacement reaction


  42. Name the gas formed in the reaction: H₂ + Cl₂ → 2HCl
     Hydrogen chloride


  43. Name the chemical equation where Zn reacts with H₂SO₄.
     Zn + H₂SO₄ → ZnSO₄ + H₂


  44. Name the acid used in the reaction: H₂SO₄ + 2KOH → K₂SO₄ + 2H₂O
     Sulphuric acid


  45. Name the base used in the reaction: HCl + NaOH → NaCl + H₂O
     Sodium hydroxide


  46. Name the products in the reaction: CaCO₃ → CaO + CO₂
     Calcium oxide and carbon dioxide


  47. Name a colour change reaction using iron and copper sulphate.
     Fe + CuSO₄ → FeSO₄ + Cu


  48. Name one evidence of chemical change in a reaction involving gas formation.
     Effervescence


  49. Name the type of reaction that involves neutralisation without gas evolution.
     Acid-base reaction


  50. Name the condition under which decomposition reactions commonly occur.
     Heating

Answer in One Word

  1. What type of change forms a new substance?
     Chemical


  2. What is the nature of a chemical change?
     Irreversible


  3. What is another name for a chemical change?
     Reaction


  4. What is the gas formed when Zn reacts with H₂SO₄?
     Hydrogen


  5. What is the solid formed in BaCl₂ + Na₂SO₄?
     Precipitate


  6. Which type of change is usually reversible?
     Physical


  7. What type of reaction combines two elements?
     Combination


  8. What type of reaction breaks a compound?
     Decomposition


  9. What type of reaction replaces one element with another?
     Displacement


  10. What type of reaction exchanges ions?
     Double displacement


  11. What type of reaction involves acid and base?
     Neutralisation


  12. Which reaction releases heat?
     Exothermic


  13. Which reaction absorbs heat?
     Endothermic


  14. What is formed when iron rusts?
     Rust


  15. What is the chemical name of rust?
     Fe₂O₃·xH₂O


  16. What is the energy required in photosynthesis?
     Sunlight


  17. What process in plants is an endothermic reaction?
     Photosynthesis


  18. What process in animals releases energy?
     Respiration


  19. What is the general form of combination reaction?
     A+B→AB


  20. What is the general form of decomposition reaction?
     AB→A+B


  21. What is the general form of displacement reaction?
     A+BC→AC+B


  22. What is the general form of double displacement reaction?
     AB+CD→AD+CB


  23. Which acid reacts with NaOH in neutralisation?
     HCl


  24. Which base reacts with HCl in neutralisation?
     NaOH


  25. What is the salt formed in HCl + NaOH?
     NaCl


  26. What is the gas evolved in CaCO₃ decomposition?
     CO₂


  27. What is the base formed in CaO + H₂O?
     Ca(OH)₂


  28. What gas is formed from 2HgO decomposition?
     Oxygen


  29. What metal is deposited in Fe + CuSO₄?
     Copper


  30. What is the precipitate in AgNO₃ + NaCl?
     AgCl


  31. What colour is AgCl precipitate?
     White


  32. Which metal is more reactive than copper?
     Zinc


  33. What product forms in C + O₂?
     CO₂


  34. What is formed when Fe rusts?
     Fe₂O₃·xH₂O


  35. What energy change happens in exothermic reactions?
     Release


  36. What energy change happens in endothermic reactions?
     Absorption


  37. What process occurs when iron is left in moist air?
     Rusting


  38. What reaction type is burning of fuel?
     Exothermic


  39. What is the base in H₂SO₄ + KOH reaction?
     KOH


  40. What is the salt in H₂SO₄ + KOH reaction?
     K₂SO₄


  41. What is the gas formed in respiration?
     CO₂


  42. What test confirms H₂ gas?
     Pop


  43. What energy drives photosynthesis?
     Light


  44. What is the process of heating CaCO₃?
     Decomposition


  45. What is the product in Zn + CuSO₄?
     ZnSO₄


  46. What gas is released when Fe reacts with steam?
     Hydrogen


  47. What gas is evolved when HCl reacts with a metal?
     Hydrogen


  48. What is a solid product that settles in liquid?
     Precipitate


  49. What is the base name of lime water?
     Ca(OH)₂


  50. What is the common term for Fe₂O₃·xH₂O?
     Rust

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  • Chapter 2: Salient Features of the Constitution — I
  • Chapter 3: Salient Features of the
  • Constitution — II
  • Chapter 4: Elections
  • Chapter 5: Local Self-Government — Rural
  • Chapter 6: Local Self-Government — Urban
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ICSE - Grade 9 - Geography

All Chapters

  • Ch 1 – Earth as a Planet
    Ch 2 – Geographic Grid: Latitudes and Longitudes
    Ch 3 – Rotation and Revolution
    Ch 4 – Earth’s Structure
    Ch 5 – Landforms of the Earth
    Ch 6 – Rocks
    Ch 7 – Volcanoes
    Ch 8 – Earthquakes
    Ch 9 – Weathering
    Ch 10 – Denudation
    Ch 11 – Hydrosphere
    Ch 12 – Composition and Structure of the Atmosphere
    Ch 13 – Insolation
    Ch 14 – Atmospheric Pressure and Winds
    Ch 15 – Humidity
    Ch 16 – Pollution
    Ch 17 – Sources of Pollution
    Ch 18 – Effects of Pollution
    Ch 19 – Preventive Measures
    Ch 20 – Natural Regions of the World

ICSE Grade 9

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Find the Odd Man Out

  1. HCl, NaOH, KOH, CaCO₃
     CaCO₃
     Explanation: CaCO₃ is a salt; others are acids or bases.


  2. Combination, Decomposition, Displacement, Melting
     Melting
     Explanation: Melting is a physical change; others are chemical reactions.


  3. H₂, O₂, CO₂, NaOH
     NaOH
     Explanation: NaOH is a base; others are gases.


  4. Rusting, Respiration, Photosynthesis, Boiling
     Boiling
     Explanation: Boiling is a physical change; others are chemical.


  5. Zn, Fe, Cu, NaCl
     NaCl
     Explanation: NaCl is a compound; others are metals.


  6. H₂SO₄, NaCl, HNO₃, HCl
     NaCl
     Explanation: NaCl is a salt; others are acids.


  7. Neutralisation, Respiration, Decomposition, Freezing
     Freezing
     Explanation: Freezing is a physical change; others are chemical reactions.


  8. CO₂, H₂, O₂, HCl
     HCl
     Explanation: HCl is an acid; others are gases.


  9. CaO + H₂O, HCl + NaOH, Fe + CuSO₄, Melting of wax
     Melting of wax
     Explanation: It’s a physical change; others are chemical reactions.


  10. Precipitate, Gas evolution, Colour change, Evaporation
     Evaporation
     Explanation: Evaporation is a physical process; others are signs of chemical change.


  11. AgNO₃, NaCl, BaCl₂, C₂H₆
     C₂H₆
     Explanation: C₂H₆ is a hydrocarbon; others are salts.


  12. NaOH, KOH, H₂O, Ca(OH)₂
     H₂O
     Explanation: H₂O is neutral; others are bases.


  13. ZnSO₄, CuSO₄, FeSO₄, NaCl
     NaCl
     Explanation: NaCl does not contain a sulphate group.


  14. Heat, Light, Sound, Precipitate
     Precipitate
     Explanation: Precipitate is a substance; others are forms of energy.


  15. Photosynthesis, Burning, Respiration, Digestion
     Photosynthesis
     Explanation: Photosynthesis is endothermic; others are exothermic.


  16. Combination, Double Displacement, Condensation, Decomposition
     Condensation
     Explanation: Condensation is a physical change; others are chemical.


  17. O₂, CO₂, N₂, HCl
     HCl
     Explanation: HCl is an acid; others are gases in air.


  18. AgCl, BaSO₄, CaCO₃, H₂
     H₂
     Explanation: H₂ is a gas; others are precipitates.


  19. A + B → AB, AB → A + B, AB + CD → AD + CB, A + B → C + D
     A + B → C + D
     Explanation: It doesn’t match standard reaction forms.


  20. Rust, Burnt paper, Melted ice, Cooking of food
     Melted ice
     Explanation: Melting is physical; others are chemical changes.


  21. Fe, Zn, Cu, NaOH
     NaOH
     Explanation: NaOH is a base; others are metals.


  22. BaCl₂, Na₂SO₄, AgNO₃, O₂
     O₂
     Explanation: O₂ is a gas; others are salts.


  23. Red litmus, Blue litmus, Phenolphthalein, NaCl
     NaCl
     Explanation: NaCl is not an indicator.


  24. CaO, CO₂, NaOH, KOH
     CO₂
     Explanation: CO₂ is acidic oxide; others are basic/alkaline substances.


  25. Respiration, Digestion, Neutralisation, Freezing
     Freezing
     Explanation: Freezing is not a chemical change.


  26. CO₂, H₂O, NaCl, CH₄
     CH₄
     Explanation: CH₄ is an organic compound; others are inorganic.


  27. Light, Heat, Colour change, Sound
     Colour change
     Explanation: Others are energy changes; colour change is a visual clue.


  28. HCl, HNO₃, H₂SO₄, CH₃OH
     CH₃OH
     Explanation: CH₃OH is an alcohol; others are acids.


  29. Decomposition, Rusting, Melting, Neutralisation
     Melting
     Explanation: It is a physical change.


  30. CaCO₃, Na₂SO₄, KOH, AgCl
     KOH
     Explanation: KOH is a base; others are salts or precipitates.


  31. H₂SO₄, Ca(OH)₂, NaOH, KOH
     H₂SO₄
     Explanation: H₂SO₄ is an acid; others are bases.


  32. Fe + CuSO₄, Zn + H₂SO₄, CaCO₃ → CaO + CO₂, Melting of wax
     Melting of wax
     Explanation: It is not a chemical reaction.


  33. Rust, Tarnish, Dissolve, Burn
     Dissolve
     Explanation: Dissolving is a physical process.


  34. CO₂, CO, NO₂, H₂O
     H₂O
     Explanation: H₂O is not an oxide of a non-metal.


  35. CaO + H₂O, CaCO₃ → CaO + CO₂, HCl + NaOH, Ice melting
     Ice melting
     Explanation: It’s a physical change.


  36. Hydrogen, Carbon dioxide, Oxygen, Sodium chloride
     Sodium chloride
     Explanation: It is a salt; others are gases.


  37. FeSO₄, CuSO₄, ZnSO₄, HCl
     HCl
     Explanation: HCl is an acid; others are salts.


  38. Silver chloride, Barium sulphate, Iron oxide, Oxygen
     Oxygen
     Explanation: It is a gas; others are solid products.


  39. Endothermic, Exothermic, Neutralisation, Crystallisation
     Crystallisation
     Explanation: It is a physical process.


  40. Vinegar, Lemon juice, Soap solution, Sulphuric acid
     Soap solution
     Explanation: It is basic; others are acidic.


  41. NaCl, KCl, CaCl₂, NH₃
     NH₃
     Explanation: NH₃ is a base; others are salts.


  42. Pop test, Flame test, Litmus test, Boiling test
     Boiling test
     Explanation: It is not a chemical test.


  43. Oxygen, Heat, Light, Carbon
     Carbon
     Explanation: Carbon is a substance; others are energy forms.


  44. Physical change, Melting, Freezing, Photosynthesis
     Photosynthesis
     Explanation: It’s a chemical change; others are physical.


  45. Lime water, Sodium hydroxide, Potassium hydroxide, Hydrochloric acid
     Hydrochloric acid
     Explanation: It’s an acid; others are bases.


  46. Baking, Combustion, Respiration, Evaporation
     Evaporation
     Explanation: Evaporation is physical; others are chemical.


  47. Fe + CuSO₄, HCl + NaOH, CaCO₃ → CaO + CO₂, Ice to water
     Ice to water
     Explanation: It is a physical change.


  48. Iron, Zinc, Silver, AgNO₃
     AgNO₃
     Explanation: It is a salt; others are metals.


  49. C + O₂ → CO₂, Zn + CuSO₄ → ZnSO₄ + Cu, H₂ + Cl₂ → 2HCl, Ice melting
     Ice melting
     Explanation: It is not a chemical reaction.


  50. Glucose, Oxygen, Carbon dioxide, Chlorophyll
     Chlorophyll
     Explanation: Chlorophyll is a pigment; others are reactants/products.

Match the Pair

Set 1: Match the chemical reaction type

Column A:

  1. Combination reaction
  2. Decomposition reaction
  3. Displacement reaction
  4. Double displacement reaction
  5. Neutralisation reaction

Column B:
 A. AB → A + B
 B. A + B → AB
 C. Acid + Base → Salt + Water
 D. AB + CD → AD + CB
 E. A + BC → AC + B

Correct Answers:
 1 – B
 2 – A
 3 – E
 4 – D
 5 – C

Set 2: Match reactions to their examples

Column A:

  1. CaCO₃ → CaO + CO₂
  2. HCl + NaOH → NaCl + H₂O
  3. Zn + H₂SO₄ → ZnSO₄ + H₂
  4. AgNO₃ + NaCl → AgCl + NaNO₃
  5. C + O₂ → CO₂

Column B:
 A. Neutralisation
 B. Decomposition
 C. Combination
 D. Displacement
 E. Double displacement

Correct Answers:
 1 – B
 2 – A
 3 – D
 4 – E
 5 – C

Set 3: Match changes with their type

Column A:

  1. Melting of ice
  2. Rusting of iron
  3. Burning of paper
  4. Dissolving salt in water
  5. Cooking of food

Column B:
 A. Physical change
 B. Physical change
 C. Chemical change
 D. Chemical change
 E. Chemical change

Correct Answers:
 1 – A
 2 – D
 3 – C
 4 – B
 5 – E

Set 4: Match observations with reactions

Column A:

  1. Gas evolution
  2. Colour change
  3. Formation of precipitate
  4. Change in temperature
  5. Release of light

Column B:
 A. Explosion
 B. Combustion
 C. Reaction of HCl and Zn
 D. Fe + CuSO₄
 E. BaCl₂ + Na₂SO₄

Correct Answers:
 1 – C
 2 – D
 3 – E
 4 – B
 5 – A

Set 5: Match chemicals to their use/type

Column A:

  1. HCl
  2. NaOH
  3. NaCl
  4. CaCO₃
  5. AgNO₃

Column B:
 A. Salt
 B. Base
 C. Acid
 D. Used to form precipitate with NaCl
 E. Metal carbonate

Correct Answers:
 1 – C
 2 – B
 3 – A
 4 – E
 5 – D

Set 6: Match reactants with products

Column A:

  1. HCl + NaOH
  2. Zn + CuSO₄
  3. CaCO₃ (heated)
  4. AgNO₃ + NaCl
  5. Fe + CuSO₄

Column B:
 A. ZnSO₄ + Cu
 B. NaCl + H₂O
 C. FeSO₄ + Cu
 D. AgCl + NaNO₃
 E. CaO + CO₂

Correct Answers:
 1 – B
 2 – A
 3 – E
 4 – D
 5 – C

Set 7: Match terms with their definitions

Column A:

  1. Precipitate
  2. Exothermic reaction
  3. Endothermic reaction
  4. Decomposition
  5. Displacement

Column B:
 A. A + BC → AC + B
 B. Solid formed in solution
 C. AB → A + B
 D. Absorbs heat
 E. Releases heat

Correct Answers:
 1 – B
 2 – E
 3 – D
 4 – C
 5 – A

Set 8: Match examples with the type of reaction

Column A:

  1. Fe + CuSO₄ → FeSO₄ + Cu
  2. C + O₂ → CO₂
  3. CaCO₃ → CaO + CO₂
  4. AgNO₃ + NaCl → AgCl + NaNO₃
  5. H₂ + Cl₂ → 2HCl

Column B:
 A. Combination
 B. Double displacement
 C. Decomposition
 D. Displacement
 E. Combination

Correct Answers:
 1 – D
 2 – A
 3 – C
 4 – B
 5 – E

Set 9: Match observations with causes

Column A:

  1. White precipitate
  2. Effervescence
  3. Sudden rise in temperature
  4. Displacement of metal
  5. Bubbles in acid + metal reaction

Column B:
 A. H₂ gas released
 B. Zn + H₂SO₄
 C. BaSO₄ formation
 D. Exothermic reaction
 E. Fe displacing Cu

Correct Answers:
 1 – C
 2 – A
 3 – D
 4 – E
 5 – B

Set 10: Match processes with type of energy change

Column A:

  1. Photosynthesis
  2. Combustion
  3. Respiration
  4. CaCO₃ → CaO + CO₂
  5. H₂ + Cl₂ → 2HCl

Column B:
 A. Endothermic
 B. Exothermic
 C. Endothermic
 D. Exothermic
 E. Exothermic

Correct Answers:
 1 – A
 2 – B
 3 – D
 4 – C
 5 – E

Short Answer Questions  

  1. What is a chemical change?
     A change in which new substances with different properties are formed.


  2. What is a physical change?
     A change in which no new substance is formed and is usually reversible.


  3. Define combination reaction.
     A reaction where two or more substances combine to form a single product.


  4. Define decomposition reaction.
     A reaction where a compound breaks down into simpler substances.


  5. What is a displacement reaction?
     A reaction in which a more reactive element displaces a less reactive one from its compound.


  6. What is a double displacement reaction?
     A reaction in which two compounds exchange ions to form new compounds.


  7. What is a neutralisation reaction?
     A reaction between an acid and a base to form salt and water.


  8. Give an example of a decomposition reaction.
     CaCO₃ → CaO + CO₂


  9. Give an example of a displacement reaction.
     Zn + CuSO₄ → ZnSO₄ + Cu


  10. Give an example of a combination reaction.
     C + O₂ → CO₂


  11. What is the white precipitate formed in AgNO₃ + NaCl?
     Silver chloride (AgCl)


  12. Which gas is evolved when Zn reacts with H₂SO₄?
     Hydrogen gas


  13. What type of change is rusting of iron?
     Chemical change


  14. What is the chemical formula of rust?
     Fe₂O₃·xH₂O


  15. What are the two main observations of a chemical change?
     Formation of a new substance and change in energy.


  16. What is an exothermic reaction?
     A reaction in which heat is released.


  17. What is an endothermic reaction?
     A reaction in which heat is absorbed.


  18. Give one example of an exothermic reaction.
     C + O₂ → CO₂


  19. Give one example of an endothermic reaction.
     CaCO₃ → CaO + CO₂


  20. What energy is used in photosynthesis?
     Solar energy


  21. What is the product of neutralisation between HCl and NaOH?
     NaCl and H₂O


  22. What is a precipitate?
     An insoluble solid formed during a chemical reaction.


  23. Which base is formed in CaO + H₂O reaction?
     Calcium hydroxide [Ca(OH)₂]


  24. Name the gas evolved when CaCO₃ is heated.
     Carbon dioxide


  25. What is the general form of a displacement reaction?
     A + BC → AC + B


  26. What is the general form of a double displacement reaction?
     AB + CD → AD + CB


  27. What is the general form of a combination reaction?
     A + B → AB


  28. Which reaction type involves exchange of ions?
     Double displacement reaction


  29. Which gas is evolved during reaction of acid with metal?
     Hydrogen gas


  30. What change occurs in the colour of Fe + CuSO₄ reaction?
     The solution turns green and copper is deposited.


  31. Why is melting of ice a physical change?
     Because no new substance is formed.


  32. What are two products of combustion of carbon?
     Carbon dioxide and heat


  33. What change indicates a chemical reaction?
     Change in temperature, colour, or formation of gas or precipitate


  34. What happens in neutralisation?
     An acid reacts with a base to form salt and water.


  35. What kind of reaction is CaCO₃ → CaO + CO₂?
     Decomposition reaction


  36. What is the solid formed in BaCl₂ + Na₂SO₄ reaction?
     Barium sulphate (BaSO₄)


  37. Is the burning of a candle a physical or chemical change?
     Chemical change


  38. What is formed when zinc reacts with sulphuric acid?
     Zinc sulphate and hydrogen gas


  39. Give one everyday example of a chemical change.
     Cooking of food


  40. What is the role of energy in chemical reactions?
     It is either absorbed or released.


  41. Name a reaction where a metal replaces another metal.
     Displacement reaction


  42. What is the product of H₂ + Cl₂?
     Hydrogen chloride (HCl)


  43. What kind of reaction is AgNO₃ + NaCl → AgCl + NaNO₃?
     Double displacement reaction


  44. What do acids turn blue litmus into?
     Red


  45. What do bases turn red litmus into?
     Blue


  46. What is formed in the reaction: Fe + CuSO₄ → ?
     FeSO₄ and Cu


  47. What kind of change is the boiling of water?
     Physical change


  48. What kind of change is the digestion of food?
     Chemical change


  49. Is light required in photosynthesis?
     Yes


  50. What kind of reaction is HCl + NaOH → NaCl + H₂O?
     Neutralisation reaction

Puzzles

  1. I’m a change that creates something new, irreversible too. What am I?
     Chemical change


  2. I’m a change that can go back, forming nothing new in fact. What am I?
     Physical change


  3. When acid and base meet, I form with water – isn’t that sweet?
     Salt


  4. I fizz and bubble and rise with pride, I’m the gas in reactions you can’t hide.
     Hydrogen


  5. Two clear solutions meet, I fall down white and neat. Who am I?
     Precipitate


  6. You mix two things and I go up high, forming a puff – I’m seen in the sky.
     Gas


  7. I’m the energy you can feel but not see, if I come out – you call it exo-me!
     Heat


  8. Add me to water, and it gets hot. I’m an oxide that’s quite a lot.
     Calcium oxide


  9. A base and acid walk into a flask, I balance them out – that’s my task.
     Neutralisation


  10. I break things down with heat in play, you call me this every day.
     Decomposition


  11. I join two friends to make one big guy, together forever, we cannot lie.
     Combination


  12. I come from the air, I rust the metal – beware!
     Oxygen


  13. I’m made when iron’s left with air and rain, reddish-brown with a stubborn stain.
     Rust


  14. I’m the brown-red metal that drops when iron shows up.
     Copper


  15. I’m a reaction where stronger kicks out weak, single metal does the sneak.
     Displacement


  16. I happen when two couples meet and swap their dance.
     Double displacement


  17. I’m the sour guest in chemistry, I turn litmus red naturally.
     Acid


  18. I’m slippery and bitter, red litmus I blue – guess who?
     Base


  19. I bubble when an acid sees me, the salt and water set me free.
     Base


  20. I’m the insoluble white that clogs your drain, you make me in labs – again and again.
     Barium sulphate


  21. I fizz when CaCO₃ meets acid, and through lime water, I make it turbid.
     Carbon dioxide


  22. I make lime water milky white, then disappear if you add me right.
     Carbon dioxide


  23. I’m the test that pops when gas is light, confirming metal-acid’s delight.
     Pop test


  24. I’m not new, not odd, I only change shape – no bond I dodge.
     Physical change


  25. I make things warmer when I’m around, you feel my energy all around.
     Exothermic reaction


  26. I absorb the heat and stay quite cool, in plants I rule.
     Endothermic reaction


  27. I’m a new solid from liquid’s dance, I settle down – I don’t take a chance.
     Precipitate


  28. I’m the silent sign – a change of shade, when reactions are properly made.
     Colour change


  29. I’m a small salt crystal, from acid and base, my neutral face wins every race.
     Sodium chloride


  30. I form when AgNO₃ meets NaCl in lab coat white.
     Silver chloride


  31. I’m the small white powder from burned magnesium bright.
     Magnesium oxide


  32. I’m a liquid compound, simple and clear – I’m water’s partner when acids are near.
     Base


  33. When metal meets acid and lets out a puff, I’m the element that’s always tough.
     Hydrogen


  34. I’m the gas that burns with a squeaky pop.
     Hydrogen


  35. I react with acid and break down rocks, my gas is caught in soda shocks.
     Calcium carbonate


  36. My fizz proves me right, my acid is tight, I vanish in lime water out of sight.
     Carbon dioxide


  37. My name sounds like fear, but I’m just rust’s peer – I come from metal and moist air.
     Oxidation


  38. I’m the reaction in your breath that lets you live and rest.
     Respiration


  39. I cook your food and change the smell, I’m chemical too – can’t you tell?
     Cooking


  40. I’m the spark in fuel’s tale, I burn and warm without fail.
     Combustion


  41. I’m the break-up caused by light, silver halide knows me right.
     Photochemical reaction


  42. I’m an equation with equal sides, keeping mass on matching rides.
     Balanced equation


  43. I am used to show the change – red to blue or vice in range.
     Indicator


  44. I am vinegar’s best acidic name – I sour the taste and win the game.
     Acetic acid


  45. I’m the strong acid in labs you see, I bubble with metal, I sting with glee.
     Hydrochloric acid


  46. My base is strong and loves to clean, slippery feel and shiny sheen.
     Sodium hydroxide


  47. I show up in salts, strong and bright – SO₄ is my suffix right.
     Sulphate


  48. I’m the hydroxide from lime and water, farmers love me like no other.
     Calcium hydroxide


  49. I look like mist, but I turn litmus red, dissolve metals and sting your head.
     Acid


  50. I’m the proof you can’t ignore – I form bubbles, heat, or change the core.
     Chemical reaction

Difference Between:

  1. Difference between Physical Change and Chemical Change
    Physical Change: No new substance is formed; usually reversible.
    Chemical Change: New substance is formed with new properties; usually irreversible.

 

  1. Difference between Combination Reaction and Decomposition Reaction
    Combination Reaction: Two or more substances combine to form a single product.
    Decomposition Reaction: A single compound breaks down into two or more simpler substances.

 

  1. Difference between Displacement and Double Displacement Reaction
    Displacement Reaction: A more reactive element replaces a less reactive one in a compound.
    Double Displacement Reaction: Two compounds exchange ions to form two new compounds.

 

  1. Difference between Acid and Base
    Acid: Sour in taste, turns blue litmus red, releases H⁺ ions in solution.
    Base: Bitter in taste, turns red litmus blue, releases OH⁻ ions in solution.

 

  1. Difference between Exothermic and Endothermic Reaction
    Exothermic Reaction: Releases heat during the reaction (e.g., combustion).
    Endothermic Reaction: Absorbs heat during the reaction (e.g., photosynthesis).

 

  1. Difference between Reactants and Products
    Reactants: Substances that take part in a chemical reaction.
    Products: Substances formed as a result of the reaction.

 

  1. Difference between Chemical Reaction and Chemical Equation
    Chemical Reaction: Actual process where substances change into new substances.
    Chemical Equation: Symbolic representation of a chemical reaction.

 

  1. Difference between Rusting and Burning
    Rusting: Slow chemical change involving iron, water, and air forming rust.
    Burning: Rapid chemical change releasing heat and light, producing oxides.

 

  1. Difference between Lime (CaO) and Slaked Lime (Ca(OH)₂)
    Lime (Calcium Oxide): A dry white solid that reacts with water exothermically.
    Slaked Lime (Calcium Hydroxide): Product formed when CaO reacts with water.

 

  1. Difference between Precipitate and Solution
    Precipitate: An insoluble solid formed in a reaction between two liquids.
    Solution: A homogeneous mixture where solute is uniformly dissolved in solvent.

 

  1. Difference between Neutralisation and Displacement Reaction
    Neutralisation Reaction: Acid reacts with base to form salt and water.
    Displacement Reaction: One element replaces another from its compound.

 

  1. Difference between Reversible and Irreversible Change
    Reversible Change: The original state can be restored (e.g., melting of ice).
    Irreversible Change: The original state cannot be restored (e.g., burning).

 

  1. Difference between Physical Property and Chemical Property
    Physical Property: Can be observed without changing the substance (e.g., colour).
    Chemical Property: Describes how a substance reacts chemically (e.g., flammability).

 

  1. Difference between Balanced and Unbalanced Chemical Equation
    Balanced Equation: Has equal number of atoms on both sides, obeying conservation of mass.
    Unbalanced Equation: Does not have equal atoms on both sides; not scientifically valid.

 

  1. Difference between Evolution of Gas and Formation of Precipitate
    Evolution of Gas: A gas is released as a product of the chemical reaction.
    Formation of Precipitate: An insoluble solid is formed in the reaction mixture.

 

  1. Difference between Laboratory Acid and Organic Acid
    Laboratory Acid: Strong acids like HCl, H₂SO₄ used in labs and industry.
    Organic Acid: Weak acids found in natural sources like vinegar (acetic acid).

 

  1. Difference between Oxidation and Reduction
    Oxidation: Gain of oxygen or loss of electrons.
    Reduction: Loss of oxygen or gain of electrons.

 

  1. Difference between Photosynthesis and Respiration
    Photosynthesis: Endothermic reaction where plants make food using sunlight.
    Respiration: Exothermic process where organisms release energy by breaking food.

 

  1. Difference between Indicator and Precipitate
    Indicator: A substance that changes colour in acidic or basic solutions.
    Precipitate: A solid that separates from a solution during a reaction.

 

  1. Difference between Chemical Change and Nuclear Change
    Chemical Change: Involves change in chemical bonds; atoms are rearranged.
    Nuclear Change: Involves change in nucleus of atom; new elements may form.

Assertion and Reason

Key to answers:
 A) Both Assertion and Reason are true and Reason is the correct explanation of Assertion
 B) Both Assertion and Reason are true but Reason is not the correct explanation of Assertion
 C) Assertion is true but Reason is false
 D) Assertion is false but Reason is true



  1.  

Assertion: Chemical changes result in the formation of new substances.
 Reason: In a chemical change, the composition of the substance remains the same.
 Answer: C



  1.  

Assertion: Rusting is a chemical change.
 Reason: A new substance, hydrated ferric oxide, is formed during rusting.
 Answer: A



  1.  

Assertion: Melting of ice is a chemical change.
 Reason: It involves the formation of a new substance.
 Answer: D



  1.  

Assertion: In a decomposition reaction, a compound breaks into simpler substances.
 Reason: Decomposition reactions are generally exothermic.
 Answer: C



  1.  

Assertion: Displacement reactions involve exchange of ions.
 Reason: Displacement reactions are the same as double displacement reactions.
 Answer: D



  1.  

Assertion: Photosynthesis is an example of an endothermic reaction.
 Reason: It requires sunlight to convert carbon dioxide and water into glucose.
 Answer: A



  1.  

Assertion: In a physical change, the substance can be recovered in its original form.
 Reason: No new substance is formed during a physical change.
 Answer: A



  1.  

Assertion: Exothermic reactions release energy in the form of heat.
 Reason: Breaking of chemical bonds absorbs energy.
 Answer: B



  1.  

Assertion: CaCO₃ decomposes to form CaO and CO₂.
 Reason: Decomposition reactions occur without heating.
 Answer: C



  1.  

Assertion: Chemical reactions always involve energy change.
 Reason: Energy is absorbed or released during bond formation and bond breaking.
 Answer: A



  1.  

Assertion: All chemical changes are reversible.
 Reason: In chemical changes, the products can be converted back to reactants easily.
 Answer: D



  1.  

Assertion: HCl + NaOH → NaCl + H₂O is a double displacement reaction.
 Reason: This reaction involves the exchange of ions between the reactants.
 Answer: A



  1.  

Assertion: Precipitation reactions form insoluble salts.
 Reason: Insoluble salts settle down as precipitate during chemical reaction.
 Answer: A



  1.  

Assertion: Colour change is an indicator of a physical change.
 Reason: Chemical changes are always colourless.
 Answer: D



  1.  

Assertion: Evolution of gas is a sign of chemical reaction.
 Reason: New substances are often formed as gases in chemical reactions.
 Answer: A



  1.  

Assertion: In displacement reactions, a less reactive element displaces a more reactive one.
 Reason: Reactivity series determines the displacement in reactions.
 Answer: C



  1.  

Assertion: Combination reactions always involve two or more reactants.
 Reason: These reactants form a single product.
 Answer: A



  1.  

Assertion: Neutralisation reactions are always endothermic.
 Reason: They result in the formation of salt and water.
 Answer: C



  1.  

Assertion: All exothermic reactions produce flames.
 Reason: Heat released in exothermic reactions is always in the form of fire.
 Answer: D



  1.  

Assertion: Formation of rust is a slow chemical change.
 Reason: Rusting requires oxygen and water over a long period.
 Answer: A



  1.  

Assertion: AgCl is a precipitate formed during a double displacement reaction.
 Reason: AgNO₃ and NaCl react to form insoluble AgCl.
 Answer: A



  1.  

Assertion: Respiration is a physical process.
 Reason: No chemical change occurs during breathing.
 Answer: D



  1.  

Assertion: Endothermic reactions release energy.
 Reason: Heat is evolved during photosynthesis.
 Answer: D



  1.  

Assertion: In double displacement reactions, gas can be evolved.
 Reason: These reactions can produce either precipitate or gas.
 Answer: A



  1.  

Assertion: Neutralisation involves the formation of salt and water.
 Reason: Acid and base combine to neutralise each other’s effect.
 Answer: A



  1.  

Assertion: Rusting is a reversible change.
 Reason: Heating rusted iron will restore the metal.
 Answer: D



  1.  

Assertion: Melting and boiling are physical changes.
 Reason: The chemical composition of the substance remains unchanged.
 Answer: A



  1.  

Assertion: The gas evolved in the reaction Zn + H₂SO₄ is oxygen.
 Reason: All metal-acid reactions evolve oxygen gas.
 Answer: D



  1.  

Assertion: CaO reacts with water to form Ca(OH)₂.
 Reason: This is a combination reaction.
 Answer: A



  1.  

Assertion: The reaction Fe + CuSO₄ → FeSO₄ + Cu is a displacement reaction.
 Reason: Iron is more reactive than copper.
 Answer: A



  1.  

Assertion: BaSO₄ is a soluble salt.
 Reason: It forms a white precipitate in water.
 Answer: C

  1.  

Assertion: Double displacement reactions occur in aqueous solutions.
 Reason: Ion exchange requires mobility of ions in solution.
 Answer: A



  1.  

Assertion: Heat is required for all chemical reactions to occur.
 Reason: Without heat, reactions cannot take place.
 Answer: D



  1.  

Assertion: A precipitate is always coloured.
 Reason: AgCl is white, so all precipitates are white or coloured.
 Answer: D



  1.  

Assertion: Evolution of hydrogen gas is observed in neutralisation.
 Reason: Hydrogen is formed when an acid reacts with a base.
 Answer: D



  1.  

Assertion: Indicators help in identifying chemical changes.
 Reason: Indicators show colour change in acid-base reactions.
 Answer: A

  1.  

Assertion: Acid + Base → Salt + Water is a displacement reaction.
 Reason: Neutralisation always results in displacement of ions.
 Answer: B



  1.  

Assertion: The decomposition of HgO is endothermic.
 Reason: Heating is required to initiate the reaction.
 Answer: A



  1.  

Assertion: Physical changes may involve change in state.
 Reason: Ice melting to water is a state change.
 Answer: A



  1.  

Assertion: In a chemical change, original substances are lost.
 Reason: New substances with different properties are formed.
 Answer: A

  1.  

Assertion: CO₂ is evolved in the reaction of metal carbonate with acid.
 Reason: Metal carbonates react with acid to release carbon dioxide.
 Answer: A



  1.  

Assertion: Burning of paper is a physical change.
 Reason: Only size of paper changes on burning.
 Answer: D



  1.  

Assertion: Combustion is an exothermic reaction.
 Reason: It releases heat and light.
 Answer: A



  1.  

Assertion: Ca(OH)₂ is formed in a neutralisation reaction.
 Reason: Lime reacts with water to form a base.
 Answer: C



  1.  

Assertion: Change in temperature indicates a chemical change.
 Reason: Heat is either absorbed or released during chemical reactions.
 Answer: A



  1.  

Assertion: H₂SO₄ + Zn → ZnSO₄ + H₂ is a double displacement reaction.
 Reason: It involves a metal replacing hydrogen.
 Answer: C



  1.  

Assertion: Gas bubbles in a reaction indicate evaporation.
 Reason: Bubbling always means liquid is boiling.
 Answer: D



  1.  

Assertion: HCl turns blue litmus red.
 Reason: HCl is an acid.
 Answer: A



  1.  

Assertion: NaOH turns red litmus blue.
 Reason: NaOH is a base.
 Answer: A



  1.  

Assertion: The formula of rust is FeSO₄.
 Reason: Rust forms by the reaction of iron with oxygen and water.
 Answer: C

True or False

  1. Chemical changes are always irreversible.
     True


  2. Physical changes result in the formation of new substances.
     False


  3. Decomposition reactions require heat to occur.
     True


  4. Combination reactions always involve a single reactant.
     False


  5. Displacement reactions involve the replacement of one element by another.
     True


  6. Melting of ice is a chemical change.
     False


  7. A precipitate is a soluble solid formed during a reaction.
     False


  8. Neutralisation reactions result in the formation of salt and water.
     True


  9. All chemical reactions absorb energy.
     False


  10. Exothermic reactions release heat energy.
     True


  11. Endothermic reactions absorb heat from the surroundings.
     True


  12. Burning of wood is a chemical change.
     True


  13. Rusting of iron can be reversed by simple physical methods.
     False


  14. A colour change is always a sign of a physical change.
     False


  15. The evolution of gas indicates a chemical reaction.
     True


  16. Photosynthesis is an exothermic reaction.
     False


  17. Respiration in living beings is an example of a chemical change.
     True


  18. Dissolving sugar in water is a chemical change.
     False


  19. CaCO₃ decomposes to form CaO and CO₂ on heating.
     True


  20. Fe + CuSO₄ → FeSO₄ + Cu is a displacement reaction.
     True


  21. NaOH is an acid.
     False


  22. AgCl is a white precipitate.
     True


  23. All neutralisation reactions are exothermic.
     True


  24. In a physical change, the composition of the substance changes.
     False


  25. Water is formed during the neutralisation of an acid and a base.
     True


  26. Heat is never involved in chemical reactions.
     False


  27. Zn displaces Cu from CuSO₄ solution.
     True


  28. Double displacement reactions involve the exchange of ions.
     True


  29. CaO + H₂O → Ca(OH)₂ is a decomposition reaction.
     False


  30. HCl reacts with NaOH to form NaCl and H₂O.
     True


  31. All chemical reactions produce gas.
     False


  32. Gas evolution, colour change, and temperature change are signs of chemical change.
     True


  33. BaSO₄ is soluble in water.
     False


  34. Precipitates are always coloured.
     False


  35. Combination reactions result in multiple products.
     False


  36. Physical changes are usually reversible.
     True


  37. All acids turn blue litmus red.
     True


  38. In the reaction of H₂ + Cl₂ → 2HCl, heat is released.
     True


  39. Chemical changes do not involve energy changes.
     False


  40. Boiling of water is a chemical change.
     False


  41. Endothermic reactions feel cold to the touch.
     True


  42. Evaporation of alcohol is a chemical change.
     False


  43. Combustion is an example of an exothermic chemical reaction.
     True


  44. Rust is formed by the reaction of iron, water, and oxygen.
     True


  45. A base reacts with another base to form salt and water.
     False


  46. Neutralisation reactions decrease acidity or basicity.
     True


  47. Ca(OH)₂ is called lime water.
     True


  48. AgNO₃ + NaCl → AgCl + NaNO₃ is a double displacement reaction.
     True


  49. Formation of bubbles always indicates boiling.
     False


  50. All chemical reactions require light to proceed.
     False

Long Answer Questions

  1. What is a chemical change? Explain with two examples.
    A chemical change is a change in which one or more new substances are formed with different properties. It is usually irreversible. Examples include rusting of iron and burning of wood.

 

  1. Define physical change. How is it different from a chemical change?
    A physical change is one in which no new substance is formed and the original substance retains its identity. It is usually reversible. A chemical change, in contrast, forms new substances and is usually irreversible.

 

  1. Describe any four characteristics of chemical reactions with examples.
    Characteristics include: (i) Evolution of gas (Zn + H₂SO₄ → ZnSO₄ + H₂), (ii) Formation of precipitate (BaCl₂ + Na₂SO₄ → BaSO₄↓ + NaCl), (iii) Change in colour (Fe + CuSO₄ → FeSO₄ + Cu), and (iv) Change in temperature (C + O₂ → CO₂ + heat).

 

  1. What is a combination reaction? Write two examples with balanced equations.
    A combination reaction is when two or more substances combine to form a single product. Examples: CaO + H₂O → Ca(OH)₂ and C + O₂ → CO₂.

 

  1. What is a decomposition reaction? Give its general equation and one example.
    A decomposition reaction involves a single compound breaking into simpler substances. General form: AB → A + B. Example: 2HgO → 2Hg + O₂.

 

  1. Explain displacement reaction with suitable examples.
    A displacement reaction occurs when a more reactive element displaces a less reactive one from its compound. Example: Zn + CuSO₄ → ZnSO₄ + Cu.

 

  1. Explain double displacement reaction with suitable examples.
    A double displacement reaction involves the exchange of ions between two compounds to form two new compounds. Example: AgNO₃ + NaCl → AgCl↓ + NaNO₃.

 

  1. What is a neutralisation reaction? Give an example.
    A neutralisation reaction is a chemical reaction in which an acid reacts with a base to form salt and water. Example: HCl + NaOH → NaCl + H₂O.

 

  1. Define exothermic reaction. Give two examples.
    An exothermic reaction is one in which heat is released. Examples include combustion (C + O₂ → CO₂ + heat) and H₂ + Cl₂ → 2HCl + heat.

 

  1. Define endothermic reaction. Give two examples.
    An endothermic reaction is a reaction in which heat is absorbed. Examples: CaCO₃ → CaO + CO₂ and photosynthesis.

 

  1. Write differences between physical and chemical changes.
    Physical changes do not form new substances and are generally reversible. Chemical changes form new substances with different properties and are usually irreversible.

 

  1. Describe the importance of chemical reactions in daily life.
    Chemical reactions are essential for digestion, cooking, respiration, rusting, combustion, and even industrial applications like making medicines and fertilizers.

 

  1. What is a precipitate? Explain with an example.
    A precipitate is an insoluble solid that forms in a solution during a chemical reaction. Example: BaCl₂ + Na₂SO₄ → BaSO₄↓ + 2NaCl.

 

  1. Describe the chemical change that occurs during the rusting of iron.
    Rusting occurs when iron reacts with oxygen and moisture to form hydrated ferric oxide (Fe₂O₃·xH₂O), commonly known as rust.

 

  1. Explain the change observed in the reaction: Fe + CuSO₄ → FeSO₄ + Cu
    Iron displaces copper from its salt solution. The solution turns green due to the formation of FeSO₄, and reddish-brown copper is deposited.

 

  1. How does temperature change indicate a chemical reaction?
    Chemical reactions often involve energy changes. If heat is released or absorbed, a noticeable temperature change occurs, indicating a chemical reaction.

 

  1. Why is burning of paper considered a chemical change?
    Burning changes the chemical composition of paper into ash, carbon dioxide, and water vapor, forming new substances.

 

  1. Explain the reaction between zinc and sulphuric acid.
    Zinc reacts with sulphuric acid to form zinc sulphate and hydrogen gas: Zn + H₂SO₄ → ZnSO₄ + H₂↑.

 

  1. What happens during photosynthesis? Is it a chemical change?
    In photosynthesis, plants convert carbon dioxide and water into glucose and oxygen using sunlight. It is an endothermic chemical reaction.

 

  1. Describe how neutralisation helps in daily life.
    Neutralisation helps in treating indigestion with antacids, correcting acidic soil using bases like lime, and reducing the sting of insect bites.

 

  1. Give two examples each of physical and chemical changes.
    Physical: melting of ice, boiling of water. Chemical: rusting of iron, digestion of food.

 

  1. Why is melting of wax a physical change?
    Melting of wax does not change its chemical composition—it only changes its state from solid to liquid.

 

  1. Why is cooking food a chemical change?
    Cooking alters the chemical composition, taste, texture, and nutrient content of the food, forming new substances.

 

  1. Describe the role of light in chemical reactions.
    Light provides the energy needed for certain chemical reactions like photosynthesis and photochemical decomposition to occur.

 

  1. What do you understand by thermal decomposition?
    Thermal decomposition is the breaking down of a compound into simpler substances using heat, like CaCO₃ → CaO + CO₂.

 

  1. Describe the test to confirm hydrogen gas.
    Bring a burning splint near the gas. If it burns with a ‘pop’ sound, hydrogen gas is present.

 

  1. Explain why AgCl is a precipitate in AgNO₃ + NaCl.
    AgCl is insoluble in water and forms as a white solid, hence it is a precipitate.

 

  1. Write a balanced chemical equation for a neutralisation reaction.
    HCl + NaOH → NaCl + H₂O

 

  1. State the observations during a chemical reaction.
    Observations include change in colour, temperature, formation of gas, or appearance of precipitate.

 

  1. How does a change in colour indicate a chemical reaction?
    A change in colour often signifies the formation of a new substance, indicating a chemical change.

 

  1. How can you say that respiration is a chemical reaction?
    Respiration converts glucose and oxygen into carbon dioxide and water with energy release—forming new substances.

 

  1. What is the importance of chemical reactions in industries?
    Chemical reactions are vital in producing cement, medicines, fuels, fertilizers, plastics, and numerous industrial materials.

 

  1. Describe a double displacement reaction with a real-world example.
    AgNO₃ + NaCl → AgCl + NaNO₃ is used in photographic films due to the sensitivity of silver chloride to light.

 

  1. How does acid react with metals? Give an equation.
    Acids react with metals to produce salt and hydrogen gas. Example: Zn + HCl → ZnCl₂ + H₂.

 

  1. What is the role of indicators in chemical changes?
    Indicators show colour changes that help detect acid-base reactions and identify the completion of a neutralisation reaction.

 

  1. What is lime water? How is it formed?
    Lime water is a solution of calcium hydroxide formed by reacting calcium oxide with water: CaO + H₂O → Ca(OH)₂.

 

  1. Give two reactions where gas is evolved.
  1. Zn + H₂SO₄ → ZnSO₄ + H₂
  2. CaCO₃ → CaO + CO₂

 

  1. How does heat affect chemical reactions?
    Heat can initiate or accelerate chemical reactions and may be absorbed or released depending on whether the reaction is endothermic or exothermic.

 

  1. State three conditions that influence chemical changes.
    Temperature, presence of light, and presence of catalysts can influence the rate and occurrence of chemical changes.

 

  1. Why is electrolysis considered a chemical change?
    Electrolysis splits compounds into different elements, forming new substances, and thus is a chemical change.

 

  1. How is respiration both a chemical change and an energy process?
    Respiration forms new substances (CO₂ and H₂O) from glucose and releases energy, fulfilling criteria for both.

 

  1. Why does cooking involve multiple chemical changes?
    Cooking causes breakdown, oxidation, and rearrangement of molecules in food, leading to the formation of new compounds.

 

  1. Why are energy changes important in chemical reactions?
    They determine whether a reaction will proceed and help classify it as exothermic or endothermic, affecting industrial and biological processes.

 

  1. Describe a test to confirm carbon dioxide gas.
    Pass the gas through lime water. If it turns milky, CO₂ is present due to formation of calcium carbonate.

 

  1. What is the significance of chemical equations?
    They represent chemical reactions in a concise and standardized way, showing reactants, products, and reaction conditions.

 

  1. Explain the use of displacement reactions in metallurgy.
    Displacement reactions are used to extract less reactive metals from their salts using more reactive metals like Al and Zn.

 

  1. How does neutralisation help in treating indigestion?
    Antacids neutralise excess hydrochloric acid in the stomach, relieving symptoms of acidity and indigestion.

 

  1. How is a precipitate reaction different from a gas evolution reaction?
    Precipitate reactions form an insoluble solid, while gas evolution reactions release a gas as a product.

 

  1. What is the significance of balanced chemical equations?
    They ensure that the mass of reactants equals the mass of products, following the law of conservation of mass.

 

  1. How can you identify a chemical change?
    By observing signs like permanent colour change, gas evolution, precipitate formation, or temperature change.

Give Reasons

  1. Give reason: Rusting of iron is a chemical change.
    Because it forms a new substance, hydrated iron(III) oxide, which has different properties from iron.

 

  1. Give reason: Melting of ice is a physical change.
    Because no new substance is formed, only the physical state of water changes.

 

  1. Give reason: Photosynthesis is an endothermic reaction.
    Because it requires sunlight (energy input) to convert carbon dioxide and water into glucose.

 

  1. Give reason: Reaction of zinc with sulphuric acid produces hydrogen gas.
    Because zinc displaces hydrogen from sulphuric acid due to its higher reactivity.

 

  1. Give reason: A precipitate is formed when BaCl₂ is added to Na₂SO₄.
    Because BaSO₄ formed is insoluble in water and settles as a solid.

 

  1. Give reason: Colour change indicates a chemical reaction.
    Because a new substance with different properties is formed during the reaction.

 

  1. Give reason: Neutralisation reactions are exothermic.
    Because heat is released when H⁺ ions from acid combine with OH⁻ ions from base to form water.

 

  1. Give reason: Combustion is a chemical change.
    Because new substances like CO₂ and water are formed, accompanied by energy release.

 

  1. Give reason: Respiration is a chemical reaction.
    Because glucose is chemically converted into carbon dioxide and water, releasing energy.

 

  1. Give reason: Formation of bubbles indicates gas evolution.
    Because the gas escapes from the solution as bubbles during the reaction.

 

  1. Give reason: Precipitation reactions are double displacement reactions.
    Because ions from two compounds exchange to form an insoluble solid (precipitate).

 

  1. Give reason: Indicators are used in acid-base reactions.
    Because they show a colour change that helps detect whether a solution is acidic or basic.

 

  1. Give reason: Heat is required in decomposition reactions.
    Because energy input is needed to break down complex compounds into simpler substances.

 

  1. Give reason: Double displacement reactions require aqueous solutions.
    Because ions need to be free to move and interact, which is possible only in solution.

 

  1. Give reason: Gas is evolved in the reaction of HCl with Zn.
    Because zinc displaces hydrogen from HCl, producing hydrogen gas.

 

  1. Give reason: The reaction between HCl and NaOH is a neutralisation reaction.
    Because acid and base react to form salt and water.

 

  1. Give reason: Silver chloride is used in photography.
    Because it is sensitive to light and decomposes to form elemental silver.

 

  1. Give reason: A burning candle shows both physical and chemical changes.
    Because melting of wax is physical, while burning of wax is chemical.

 

  1. Give reason: Exothermic reactions raise the temperature of surroundings.
    Because heat energy is released into the environment during the reaction.

 

  1. Give reason: Calcium hydroxide solution is called lime water.
    Because it is formed by dissolving calcium hydroxide in water, traditionally known as lime.

 

  1. Give reason: Rust cannot be changed back to iron by physical means.
    Because rusting is a chemical change that alters the composition of iron.

 

  1. Give reason: Zn + CuSO₄ → ZnSO₄ + Cu is a displacement reaction.
    Because zinc, being more reactive, displaces copper from its salt solution.

 

  1. Give reason: A chemical equation must be balanced.
    Because it must obey the law of conservation of mass.

 

  1. Give reason: CaCO₃ decomposes on heating.
    Because heat provides the energy required to break it into CaO and CO₂.

 

  1. Give reason: Boiling of water is not a chemical change.
    Because the composition of water remains unchanged—it only changes from liquid to gas.

 

  1. Give reason: Neutralisation reactions are useful in treating indigestion.
    Because antacids neutralise excess stomach acid, relieving discomfort.

 

  1. Give reason: A change in colour of a solution suggests a chemical change.
    Because the formation of a new substance alters the visual appearance.

 

  1. Give reason: Indicators are not needed in salt-salt reactions.
    Because there’s no acid or base to detect with colour change.

 

  1. Give reason: Combustion of fuels is highly exothermic.
    Because it releases large amounts of heat and light energy.

 

  1. Give reason: CaO + H₂O → Ca(OH)₂ is a combination reaction.
    Because two reactants combine to form a single product.

 

  1. Give reason: The formation of FeSO₄ from Fe and CuSO₄ is a redox reaction.
    Because iron is oxidised and copper is reduced during the reaction.

 

  1. Give reason: Evolution of heat in a reaction proves it is exothermic.
    Because the system releases energy to the surroundings.

 

  1. Give reason: H₂ is a combustible gas.
    Because it reacts with oxygen and releases energy in the form of heat and light.

 

  1. Give reason: The reaction of baking soda and vinegar produces bubbles.
    Because carbon dioxide gas is evolved during the chemical reaction.

 

  1. Give reason: CaCO₃ turns lime water milky.
    Because CO₂ reacts with Ca(OH)₂ to form insoluble CaCO₃, which appears milky.

 

  1. Give reason: Burning of magnesium ribbon forms a white powder.
    Because it reacts with oxygen to form magnesium oxide.

 

  1. Give reason: Chemical changes often cannot be reversed.
    Because new substances with different chemical compositions are formed.

 

  1. Give reason: Indicators are used in titrations.
    Because they help determine the endpoint by changing colour.

 

  1. Give reason: Silver nitrate forms white precipitate with sodium chloride.
    Because silver chloride is insoluble in water.

 

  1. Give reason: Formation of curd from milk is a chemical change.
    Because new substances with different taste and texture are formed.

 

  1. Give reason: Heat causes chemical decomposition of compounds like HgO.
    Because thermal energy breaks the bonds holding atoms together in a compound.

 

  1. Give reason: Carbon dioxide does not support combustion.
    Because it does not react with other substances to produce heat or light.

 

  1. Give reason: Fire extinguishers contain CO₂.
    Because CO₂ displaces oxygen and cools the fire, preventing combustion.

 

  1. Give reason: Vinegar is used to remove limescale.
    Because it reacts with calcium carbonate (basic) in the scale and dissolves it.

 

  1. Give reason: The reaction between H₂ and Cl₂ forms HCl.
    Because hydrogen and chlorine combine chemically to form hydrogen chloride.

 

  1. Give reason: Milk spoiling is a chemical change.
    Because it results in formation of new substances with sour taste and smell.

 

  1. Give reason: In most reactions, atoms are neither created nor destroyed.
    Because chemical reactions follow the law of conservation of mass.

 

  1. Give reason: Heating sugar results in black residue.
    Because it decomposes, releasing water and leaving carbon behind.

 

  1. Give reason: Iron is stored dry to prevent rusting.
    Because moisture and oxygen cause rust formation.

 

  1. Give reason: Reaction rate increases with temperature.
    Because particles move faster and collide more energetically at higher temperatures.

Arrange the Words 

Case Studies

Case Study 1
 Ravi mixed dilute hydrochloric acid with zinc granules in a test tube. Soon, he observed bubbles coming out and the test tube became warm.
 Q1. What type of reaction is this?
 Displacement reaction
 Q2. What gas is evolved?
 Hydrogen

 

Case Study 2
 While experimenting in the lab, Meena added barium chloride to sodium sulphate. A white solid settled at the bottom.
 Q1. What is the white solid called?
 Precipitate
 Q2. Which type of chemical reaction is this?
 Double displacement reaction

 

Case Study 3
 An iron nail was placed in a blue copper sulphate solution. After some time, the blue colour faded and a reddish-brown layer formed on the nail.
 Q1. What is the brown layer?
 Copper
 Q2. What type of reaction occurred?
 Displacement reaction

 

Case Study 4
 During an outdoor class demonstration, the teacher burned magnesium ribbon in air. A bright white light was produced, and white ash remained.
 Q1. What is the white ash?
 Magnesium oxide
 Q2. What type of reaction occurred?
 Combination reaction

 

Case Study 5
 In a chemistry lab, a student added dilute sulphuric acid to calcium carbonate. Gas bubbles were released and turned lime water milky.
 Q1. Which gas is released?
 Carbon dioxide
 Q2. What type of reaction is this?
 Acid-carbonate reaction (chemical change)

 

Case Study 6
 A solution of sodium hydroxide was added to hydrochloric acid. The temperature of the container increased.
 Q1. What type of reaction is this?
 Neutralisation
 Q2. Is this reaction exothermic or endothermic?
 Exothermic

 

Case Study 7
 Lime (CaO) was mixed with water, and heat was released. The solution turned basic.
 Q1. Which compound is formed?
 Calcium hydroxide
 Q2. What type of reaction is this?
 Combination reaction

 

Case Study 8
 A student placed silver nitrate solution in a beaker and added a few drops of sodium chloride solution. A white curdy solid was observed.
 Q1. What is the white solid formed?
 Silver chloride
 Q2. What type of reaction occurred?
 Double displacement

 

Case Study 9
 When sugar is heated strongly, it melts, then turns brown, and finally black.
 Q1. What is the black residue?
 Carbon
 Q2. Is this change chemical or physical?
 Chemical

 

Case Study 10
 Dilute hydrochloric acid was added to magnesium ribbon. Bubbles formed and hydrogen gas was collected.
 Q1. Write the balanced chemical equation for this reaction.
 Mg + 2HCl → MgCl₂ + H₂
 Q2. What is the evidence of chemical reaction here?
 Gas evolution

 

Case Study 11
 In a science experiment, calcium carbonate was heated in a test tube. A colourless gas was released and the residue was a white solid.
 Q1. What is the name of the gas evolved?
 Carbon dioxide
 Q2. Name the white residue.
 Calcium oxide

 

Case Study 12
 While making soap, Priya mixed an acid with a base and observed the solution became warm.
 Q1. What is this type of reaction called?
 Neutralisation
 Q2. What are the products formed?
 Salt and water

 

Case Study 13
 A student added blue litmus solution to lemon juice. The colour changed to red.
 Q1. What does this colour change indicate?
 Presence of acid
 Q2. Is lemon juice acidic or basic?
 Acidic

 

Case Study 14
 Aluminium foil was dipped in iron sulphate solution. No visible change occurred.
 Q1. Why is there no reaction?
 Aluminium is more reactive than iron but cannot displace it from sulphate solution
 Q2. What type of reaction is this supposed to be?
 Displacement (did not occur due to reactivity issues)

 

Case Study 15
 Milk left outside during summer turned sour.
 Q1. What type of change has occurred?
 Chemical change
 Q2. Name the acid formed.
 Lactic acid

 

Case Study 16
 During a demonstration, the teacher decomposed lead nitrate by heating it. Brown fumes were observed.
 Q1. What type of reaction occurred?
 Decomposition reaction
 Q2. What gas is evolved during this reaction?
 Nitrogen dioxide

 

Case Study 17
 When food is cooked, it changes in colour, smell, and taste.
 Q1. Is this a chemical or physical change?
 Chemical change
 Q2. Why?
 Because new substances are formed

 

Case Study 18
 A student added baking soda to vinegar. Bubbles formed immediately.
 Q1. What gas was released?
 Carbon dioxide
 Q2. What proves a chemical reaction occurred?
 Effervescence (bubbling of gas)

 

Case Study 19
 Copper oxide was mixed with hydrochloric acid, producing a blue-green solution.
 Q1. Name the salt formed.
 Copper(II) chloride
 Q2. What type of reaction is this?
 Neutralisation reaction

 

Case Study 20
 A metal was added to dilute sulphuric acid and hydrogen gas evolved.
 Q1. What is the general reaction of metal with acid?
 Metal + Acid → Salt + Hydrogen gas
 Q2. Is this reaction endothermic or exothermic?
 Exothermic

Numericals

Numeric problems are not available for this chapter.

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