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Q1. What happens when ferrous sulphate crystals are heated strongly?
• They melt without any change.
• They change colour and decompose into simpler products.
• They combine with oxygen to form a new compound.
• They dissolve into a liquid.
Answer: They change colour and decompose into simpler products.
On heating, the green ferrous sulphate crystals decompose into ferric oxide, sulphur dioxide, and sulphur trioxide. This is a decomposition reaction.
Q2. What type of reaction is shown by: 2FeSO₄(s) + Heat → Fe₂O₃(s) + SO₂(g) + SO₃(g)?
• Combination reaction
• Displacement reaction
• Decomposition reaction
• Double displacement reaction
Answer: Decomposition reaction
In this reaction, a single reactant (ferrous sulphate) breaks down to give simpler products. This is a decomposition reaction.
Q3. What is the characteristic odour observed when heating ferrous sulphate crystals?
• Odour of ammonia
• Odour of burning sulphur
• Sweet smell
• No smell
Answer: Odour of burning sulphur
The text states you can smell the characteristic odour of burning sulphur during the decomposition.
Q4. What are the gaseous products of the thermal decomposition of ferrous sulphate?
• Oxygen and nitrogen
• Sulphur dioxide and sulphur trioxide
• Carbon dioxide and water vapour
• Hydrogen and oxygen
Answer: Sulphur dioxide and sulphur trioxide
The decomposition products are ferric oxide (solid), sulphur dioxide (gas), and sulphur trioxide (gas).
Q5. What is the solid product formed when calcium carbonate is heated strongly?
• Calcium hydroxide
• Calcium oxide
• Calcium chloride
• Calcium sulphate
Answer: Calcium oxide
Calcium carbonate decomposes on heating to form calcium oxide (quick lime) and carbon dioxide.
Q6. Quick lime
• Slaked lime
• Limestone
Answer: Quick lime
Calcium oxide is called lime or quick lime. It is used in the manufacture of cement.
Q7. What type of decomposition reaction is carried out by heating?
• Electrolytic decomposition
• Photolytic decomposition
• Thermal decomposition
• Double decomposition
Answer: Thermal decomposition
When a decomposition reaction is carried out by heating, it is called thermal decomposition.
Q8. What are the brown fumes observed when lead nitrate is heated?
• Nitrogen gas
• Oxygen gas
• Nitrogen dioxide gas
• Sulphur dioxide gas
Answer: Nitrogen dioxide gas
The emission of brown fumes is of nitrogen dioxide (NO₂), produced during the thermal decomposition of lead nitrate.
Q9. In the decomposition of lead nitrate, what is the other gas produced along with nitrogen dioxide?
• Hydrogen
• Oxygen
• Carbon dioxide
• Sulphur trioxide
Answer: Oxygen
Lead nitrate decomposes to form lead oxide, nitrogen dioxide, and oxygen gas (O₂).
Q10. What is the process of decomposing water into hydrogen and oxygen by passing electricity called?
• Hydrolysis
• Electrolysis
• Thermolysis
• Photolysis
Answer: Electrolysis
electrolysis of water using carbon electrodes and a battery to decompose it into gases.
Q11. What is added to water to make it conduct electricity during its electrolysis?
• Common salt
• Sugar
• A few drops of dilute sulphuric acid
• Soap solution
Answer: A few drops of dilute sulphuric acid
To facilitate electrolysis, a few drops of dilute sulphuric acid are added to the water.
Q12. What are the two gases produced during the electrolysis of water?
• Oxygen and chlorine
• Hydrogen and oxygen
• Hydrogen and chlorine
• Nitrogen and oxygen
Answer: Hydrogen and oxygen
Electrolysis of water decomposes it into hydrogen and oxygen gases, collected over the electrodes.
Q13. In a double displacement reaction between sodium sulphate and barium chloride, what is observed?
• A coloured gas is evolved.
• A white precipitate is formed.
• The solution turns blue.
• The mixture gets hot.
Answer: A white precipitate is formed.
Mixing the two solutions produces a white, insoluble substance called a precipitate (barium sulphate).
Q14. What is the chemical name of the white precipitate formed in the reaction: Na₂SO₄ + BaCl₂ → ?
• Sodium chloride
• Barium sulphate
• Sodium sulphate
• Barium chloride
Answer: Barium sulphate
The balanced equation is Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq). The precipitate is barium sulphate (BaSO₄).
Q15. What type of reaction is Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq)?
• Combination
• Decomposition
• Displacement
• Double displacement
Answer: Double displacement
Reactions where there is an exchange of ions between reactants to form new compounds are called double displacement reactions.
Q16. In a double displacement reaction, what happens between the reactants?
• One element displaces another.
• A single compound breaks down.
• Two compounds exchange ions.
• Two elements combine.
Answer: Two compounds exchange ions.
Such reactions involve an exchange of ions between the reactants, forming new compounds.
Q17. What is another name for a reaction that produces an insoluble solid?
• Redox reaction
• Precipitation reaction
• Neutralization reaction
• Combustion reaction
Answer: Precipitation reaction
Any reaction that produces a precipitate (insoluble solid) can be called a precipitation reaction.
Q18. In the double displacement reaction between lead nitrate and potassium iodide, what is the colour of the precipitate?
• White
• Blue
• Black
• Yellow
Answer: Yellow
a yellow precipitate of lead iodide is formed.
Q19. What remains dissolved in the solution after the reaction between sodium sulphate and barium chloride?
• Barium sulphate
• Sodium chloride
• Sodium sulphate
• Barium chloride
Answer: Sodium chloride
The other product, sodium chloride (NaCl), is soluble and remains in the solution.
Q20. Which ions combine to form the precipitate in the reaction between sodium sulphate and barium chloride?
• Na⁺ and Cl⁻
• Ba²⁺ and SO₄²⁻
• Na⁺ and SO₄²⁻
• Ba²⁺ and Cl⁻
Answer: Ba²⁺ and SO₄²⁻
The white precipitate of BaSO₄ is formed by the reaction between barium ions (Ba²⁺) and sulphate ions (SO₄²⁻).
Q21. What is the physical state of barium sulphate (BaSO₄) in the chemical equation?
• (aq)
• (g)
• (l)
• (s)
Answer: (s)
Barium sulphate is the insoluble precipitate, so its state is represented as solid (s).
Q22. In the reaction between sodium sulphate and barium chloride, which substance is responsible for the formation of the white precipitate?
• Sodium ions and chloride ions
• Barium ions and sulphate ions
• Sodium ions and sulphate ions
• Barium ions and chloride ions
Answer: Barium ions and sulphate ions
The precipitate is barium sulphate (BaSO₄). It forms when barium ions (Ba²⁺) from barium chloride combine with sulphate ions (SO₄²⁻) from sodium sulphate.
Q23. The decomposition of water into hydrogen and oxygen by electricity is an example of what?
• Thermal decomposition
• Electrolytic decomposition
• Photolytic decomposition
• Double decomposition
Answer: Electrolytic decomposition
Decomposition caused by electricity is called electrolytic decomposition. The electrolysis of water is an example.
Q24. Which industry uses the thermal decomposition of calcium carbonate?
• Textile industry
• Cement industry
• Paper industry
• Steel industry
Answer: Cement industry
Calcium oxide (quick lime) produced from limestone (CaCO₃) is used in the manufacture of cement.
Q25. What is the chemical formula of the compound that loses water to become anhydrous before decomposing?
• Fe₂O₃
• FeSO₄·7H₂O
• CaCO₃
• Pb(NO₃)₂
Answer: FeSO₄·7H₂O
Ferrous sulphate crystals (FeSO₄·7H₂O) lose their water of crystallisation first when heated.
Q26. What is the purpose of adding dilute sulphuric acid to water in the electrolysis activity?
• To make the water acidic
• To make the water coloured
• To make the water conduct electricity better
• To produce more gas
Answer: To make the water conduct electricity better
Pure water is a poor conductor. Adding a few drops of dilute acid increases its conductivity for electrolysis.
Q27. In the decomposition of lead nitrate, what is the solid product?
• Lead dioxide
• Lead oxide
• Lead sulphate
• Lead chloride
Answer: Lead oxide
The decomposition reaction is: 2Pb(NO₃)₂(s) → 2PbO(s) + 4NO₂(g) + O₂(g). The solid product is lead oxide (PbO).
Q28. What is the key visual change indicating a decomposition reaction has occurred in Activity 5.5?
• Formation of a precipitate
• Change in colour of the crystals
• Evolution of a gas with a pop sound
• The crystals dissolve
Answer: Change in colour of the crystals
The green colour of ferrous sulphate crystals changes upon heating, indicating decomposition.
Q29. In a precipitation reaction, the insoluble solid formed is called what?
• Solute
• Solvent
• Precipitate
• Effervescence
Answer: Precipitate
The insoluble substance that separates from the solution is known as a precipitate.
Q30. What must be carefully handled by the teacher in the electrolysis of water activity?
• The plastic mug
• The battery
• Testing the gases with a burning candle
• Adding sulphuric acid
Answer: Testing the gases with a burning candle
A caution note states that testing the gases (hydrogen and oxygen) with a burning candle must be performed carefully by the teacher due to the risk of explosion.
Q31. What is the ratio of gases produced during the electrolysis of water?
• Equal volumes
• Twice as much hydrogen as oxygen
• Twice as much oxygen as hydrogen
• No fixed ratio
Answer: Twice as much hydrogen as oxygen
Water (H₂O) decomposes into two molecules of hydrogen and one molecule of oxygen, so the volume of hydrogen gas collected is twice that of oxygen.
Q32. What is the chemical name of the compound precipitated in the recalled Activity 5.2?
• Potassium nitrate
• Lead iodide
• Lead nitrate
• Potassium chloride
Answer: Lead iodide
The reaction between lead nitrate and potassium iodide forms a yellow precipitate of lead iodide (PbI₂).
Q33. Which of the following is NOT a product of heating lead nitrate?
• Lead oxide
• Nitrogen
• Nitrogen dioxide
• Oxygen
Answer: Nitrogen
The products are lead oxide (PbO), nitrogen dioxide (NO₂), and oxygen (O₂). Nitrogen gas (N₂) is not produced.
Q34. What is the state symbol for sulphur dioxide in the decomposition of ferrous sulphate?
• (s)
• (l)
• (g)
• (aq)
Answer: (g)
Sulphur dioxide (SO₂) is a gas, so it is represented by (g).
Q35. What is the primary reason for calling the reaction between sodium sulphate and barium chloride a double displacement?
• Heat is evolved.
• Ions are exchanged.
• A single product is formed.
• An element is displaced.
Answer: Ions are exchanged.
It is a double displacement reaction because there is an exchange of ions (Ba²⁺ with SO₄²⁻ and Na⁺ with Cl⁻) between the reactants.
Q36. What happens to the colour of lead nitrate crystals upon heating?
• They turn green.
• They turn white.
• They emit brown fumes and decompose.
• They become blue.
Answer: They emit brown fumes and decompose.
Heating lead nitrate causes it to decompose, emitting brown fumes of nitrogen dioxide.
Q37. In the context of decomposition reactions, what does the term “thermal” refer to?
• Light
• Electricity
• Heat
• Pressure
Answer: Heat
“Thermal” relates to heat. Thermal decomposition means decomposition caused by heating.
Q38. What is the common feature between the decomposition of ferrous sulphate, calcium carbonate, and lead nitrate?
• They all produce oxygen gas.
• They are all caused by electricity.
• They all involve a single reactant breaking down on heating.
• They all produce a precipitate.
Answer: They all involve a single reactant breaking down on heating.
They are all examples of thermal decomposition reactions where a single compound breaks down into simpler substances upon heating.
Q39. What is the valency of the sulphate ion (SO₄²⁻)?
• 1
• 2
• 3
• 4
Answer: 2
The sulphate ion has a charge of -2, as indicated by its formula SO₄²⁻.
Q40. What gas is tested by bringing a burning candle close and produces a pop sound?
• Oxygen
• Nitrogen dioxide
• Hydrogen
• Carbon dioxide
Answer: Hydrogen
Hydrogen gas burns with a pop sound. This test is part of the electrolysis of water activity.
Q41. Quick lime
• Calcium oxide
Answer: Carbon dioxide
Carbon dioxide (CO₂) is released and is a known greenhouse gas.
Q42. Quick lime (CaO) is produced by the thermal decomposition of limestone (CaCO₃).
• Slaked lime
• Limestone (Calcium carbonate)
• Marble chips
• Ferrous sulphate
Answer: Limestone (Calcium carbonate)
Q43. In the ionic exchange of Na₂SO₄ and BaCl₂, which ion from BaCl₂ combines with SO₄²⁻?
• Cl⁻
• Na⁺
• Ba²⁺
• O²⁻
Answer: Ba²⁺
Barium ion (Ba²⁺) from barium chloride combines with sulphate ion (SO₄²⁻) from sodium sulphate to form BaSO₄.
Q44. What is the colour of ferrous sulphate crystals before heating?
• White
• Blue
• Green
• Yellow
Answer: Green
The activity mentions noting the green colour of the ferrous sulphate crystals initially.
Q45. What does the arrow with “Heat” written above it in a chemical equation indicate?
• The reaction is reversible.
• Heat is absorbed.
• The reaction requires heating to proceed.
• The reaction gives out heat.
Answer: The reaction requires heating to proceed.
It indicates that heat is supplied for the reaction to occur, as in thermal decomposition.
Q46. What is the main industrial use of the decomposition reaction of calcium carbonate?
• To make plaster of Paris
• To make cement
• To make glass
• To make soap
Answer: To make cement
The quick lime (CaO) produced is used in the manufacture of cement.
Q47. What is the specific term for the decomposition reaction carried out using electricity, as shown with water?
• Thermal Decomposition
• Photolytic Decomposition
• Electrolytic Decomposition
• Catalytic Decomposition
Answer: Electrolytic Decomposition
The text describes using a battery and electrodes to decompose water. Decomposition caused by electricity is called electrolytic decomposition.
Q48. What is the other name for a double displacement reaction that produces a precipitate?
• Neutralization
• Precipitation
• Combustion
• Redox
Answer: Precipitation
When a double displacement reaction results in the formation of an insoluble solid, it is specifically called a precipitation reaction.
Q49. In the decomposition of ferrous sulphate, what is the fate of the water molecules in the crystal?
• They react to form sulphuric acid.
• They are released as water vapour initially.
• They become part of the sulphur dioxide.
• They are not affected.
Answer: They are released as water vapour initially.
Ferrous sulphate crystals (FeSO₄·7H₂O) first lose their water of crystallisation upon heating before further decomposition.
Q50. What fundamental principle do decomposition reactions demonstrate?
• A compound can be broken into its constituent elements or simpler compounds.
• Two elements always combine to form a compound.
• Ions must always be exchanged.
• All reactions need a catalyst.
Answer: A compound can be broken into its constituent elements or simpler compounds.
Decomposition reactions show that a single reactant (compound) can break down into two or more simpler substances (elements or compounds) under suitable conditions.