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Q1. What happens when ferrous sulphate crystals are heated strongly?
They change colour and decompose into simpler products.Upon strong heating, green ferrous sulphate crystals first lose water of crystallization and turn white, then decompose into reddish-brown ferric oxide, sulphur dioxide, and sulphur trioxide gases, showing both colour change and breakdown into simpler substances.
Q2. What type of reaction is shown by: 2FeSO₄(s) + Heat → Fe₂O₃(s) + SO₂(g) + SO₃(g)?
Decomposition reactionA single reactant (ferrous sulphate) breaks down into two or more products (ferric oxide, sulphur dioxide, sulphur trioxide) upon heating, which is the defining feature of a thermal decomposition reaction.
Q3. What is the characteristic odour observed when heating ferrous sulphate crystals?
Odour of burning sulphurThe gaseous products include sulphur dioxide (SO₂) and sulphur trioxide (SO₃), both of which have the characteristic pungent smell of burning sulphur.
Q4. What are the gaseous products of the thermal decomposition of ferrous sulphate?
Sulphur dioxide and sulphur trioxideFrom the balanced equation 2FeSO₄ → Fe₂O₃ + SO₂ + SO₃, the two gases released are sulphur dioxide and sulphur trioxide.
Q5. What is the solid product formed when calcium carbonate is heated strongly?
Calcium oxideThermal decomposition of calcium carbonate (CaCO₃) produces calcium oxide (CaO) and carbon dioxide gas (CO₂). CaO is the solid residue.
Q6. Which substance is produced by the thermal decomposition of limestone in the cement industry?
Quick limeLimestone (calcium carbonate) is heated in kilns to produce quick lime (calcium oxide, CaO), which is a key ingredient in cement manufacturing.
Q7. What type of decomposition reaction is carried out by heating?
Thermal decomposition“Thermal” means heat. When a single compound breaks down into simpler substances due to heat energy, it is specifically called thermal decomposition.
Q8. What are the brown fumes observed when lead nitrate is heated?
Nitrogen dioxide gasLead nitrate decomposes as 2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂. Nitrogen dioxide (NO₂) is a reddish-brown gas with a pungent odour.
Q9. In the decomposition of lead nitrate, what is the other gas produced along with nitrogen dioxide?
OxygenThe balanced equation shows that along with nitrogen dioxide (NO₂), oxygen gas (O₂) is also produced from the breakdown of the nitrate groups.
Q10. What is the process of decomposing water into hydrogen and oxygen by passing electricity called?
ElectrolysisElectrolysis is the process where an electric current is passed through a substance (here water) to cause a chemical decomposition.
Q11. What is added to water to make it conduct electricity during its electrolysis?
A few drops of dilute sulphuric acidPure water is a poor conductor. Adding a few drops of dilute sulphuric acid provides ions (H⁺ and SO₄²⁻) that increase electrical conductivity without interfering with the products.
Q12. What are the two gases produced during the electrolysis of water?
Hydrogen and oxygenWater (H₂O) decomposes into its constituent elements: hydrogen gas (H₂) at the cathode and oxygen gas (O₂) at the anode.
Q13. In a double displacement reaction between sodium sulphate and barium chloride, what is observed?
A white precipitate is formed.Barium sulphate (BaSO₄) is insoluble in water and appears as a white solid precipitate immediately upon mixing the two clear solutions.
Q14. What is the chemical name of the white precipitate formed in the reaction: Na₂SO₄ + BaCl₂ → ?
Barium sulphateThe reaction is Na₂SO₄ + BaCl₂ → BaSO₄ (white precipitate) + 2NaCl. The precipitate is barium sulphate.
Q15. What type of reaction is Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq)?
Double displacementTwo compounds exchange their ions: the Na⁺ from sodium sulphate swaps with the Ba²⁺ from barium chloride, forming two new compounds.
Q16. In a double displacement reaction, what happens between the reactants?
Two compounds exchange ions.The prefix “double” indicates two exchanges. Ions from the two reactants swap partners to form two new products.
Q17. What is another name for a reaction that produces an insoluble solid?
Precipitation reactionThe insoluble solid formed is called a “precipitate,” so the reaction is specifically named a precipitation reaction.
Q18. In the double displacement reaction between lead nitrate and potassium iodide, what is the colour of the precipitate?
YellowPb(NO₃)₂ + 2KI → PbI₂ (yellow precipitate) + 2KNO₃. Lead iodide is bright yellow and insoluble.
Q19. What remains dissolved in the solution after the reaction between sodium sulphate and barium chloride?
Sodium chlorideBarium sulphate precipitates out. Sodium chloride (NaCl) is soluble in water and remains in the aqueous solution.
Q20. Which ions combine to form the precipitate in the reaction between sodium sulphate and barium chloride?
Ba²⁺ and SO₄²⁻The precipitate is barium sulphate (BaSO₄), formed by the combination of barium ions (Ba²⁺) and sulphate ions (SO₄²⁻).
Q21. What is the physical state of barium sulphate (BaSO₄) in the chemical equation?
(s)(s) stands for solid. Since BaSO₄ is insoluble and forms a precipitate, it is written with the (s) state symbol.
Q22. In the reaction between sodium sulphate and barium chloride, which substance is responsible for the formation of the white precipitate?
Barium ions and sulphate ionsThe white precipitate is BaSO₄, so it is specifically the combination of Ba²⁺ (from barium chloride) and SO₄²⁻ (from sodium sulphate) that causes precipitation.
Q23. The decomposition of water into hydrogen and oxygen by electricity is an example of what?
Electrolytic decompositionWhen electrical energy is used to break down a compound, it is called electrolytic decomposition.
Q24. Which industry uses the thermal decomposition of calcium carbonate?
Cement industryCement manufacturing involves heating limestone (CaCO₃) in rotary kilns to produce quick lime (CaO), which then reacts with other materials to form cement clinker.
Q25. What is the chemical formula of the compound that loses water to become anhydrous before decomposing?
FeSO₄·7H₂OFerrous sulphate heptahydrate (green crystals) first loses its 7 water molecules on heating to become anhydrous ferrous sulphate (white), which then decomposes further.
Q26. What is the purpose of adding dilute sulphuric acid to water in the electrolysis activity?
To make the water conduct electricity betterDilute H₂SO₄ provides free H⁺ and SO₄²⁻ ions, significantly increasing the electrical conductivity of water so that electrolysis can proceed efficiently.
Q27. In the decomposition of lead nitrate, what is the solid product?
Lead oxide2Pb(NO₃)₂ → 2PbO (yellow when hot, white when cold) + 4NO₂ + O₂. The solid residue is lead(II) oxide.
Q28. What is the key visual change indicating a decomposition reaction has occurred in Activity 5.5?
Change in colour of the crystalsIn the ferrous sulphate decomposition activity, the green crystals turn white (loss of water) and then change to reddish-brown (formation of Fe₂O₃), clearly showing a reaction.
Q29. In a precipitation reaction, the insoluble solid formed is called what?
PrecipitateThe term “precipitate” specifically refers to the solid that forms and separates from a solution during a chemical reaction.
Q30. What must be carefully handled by the teacher in the electrolysis of water activity?
Adding sulphuric acidSulphuric acid is corrosive and can cause severe burns, so its addition should be done carefully by the teacher, not by students.
Q31. What is the ratio of gases produced during the electrolysis of water?
Twice as much hydrogen as oxygenWater is H₂O. Electrolysis produces 2 volumes of H₂ for every 1 volume of O₂ (volume ratio 2:1).
Q32. What is the chemical name of the compound precipitated in the recalled Activity 5.2?
Lead iodideActivity 5.2 involves the reaction between lead nitrate and potassium iodide, producing yellow precipitate of lead iodide (PbI₂).
Q33. Which of the following is NOT a product of heating lead nitrate?
NitrogenThe products are lead oxide (PbO), nitrogen dioxide (NO₂), and oxygen (O₂). Nitrogen gas (N₂) is not produced in this reaction.
Q34. What is the state symbol for sulphur dioxide in the decomposition of ferrous sulphate?
(g)Sulphur dioxide (SO₂) is produced as a gas, so its state symbol is (g) for gas.
Q35. What is the primary reason for calling the reaction between sodium sulphate and barium chloride a double displacement?
Ions are exchanged.Two ionic compounds exchange their ions (Na⁺ swaps with Ba²⁺, SO₄²⁻ swaps with Cl⁻), which is the defining characteristic of double displacement.
Q36. What happens to the colour of lead nitrate crystals upon heating?
They emit brown fumes and decompose.Lead nitrate crystals decompose with crackling, producing brown fumes of nitrogen dioxide (NO₂), leaving behind yellow lead oxide.
Q37. In the context of decomposition reactions, what does the term “thermal” refer to?
Heat“Thermal” comes from the Greek word “therme,” meaning heat. Thermal decomposition requires heat energy to break down a compound.
Q38. What is the common feature between the decomposition of ferrous sulphate, calcium carbonate, and lead nitrate?
They all involve a single reactant breaking down on heating.All three are thermal decomposition reactions where one compound breaks into simpler substances when heated.
Q39. What is the valency of the sulphate ion (SO₄²⁻)?
2The superscript 2⁻ indicates that the sulphate ion carries a charge of -2, meaning its valency is 2.
Q40. What gas is tested by bringing a burning candle close and produces a pop sound?
HydrogenHydrogen gas is highly flammable. When a burning splint or candle is brought near hydrogen, it burns rapidly with a characteristic “pop” sound.
Q41. What is the common name of calcium oxide (CaO)?
Quick limeCalcium oxide (CaO) is commonly called quick lime. It is produced by heating limestone and is highly reactive with water.
Q42. Quick lime (CaO) is produced by the thermal decomposition of which substance?
Limestone (Calcium carbonate)CaCO₃ → CaO + CO₂. Limestone, which is chemically calcium carbonate, decomposes on strong heating to give quick lime.
Q43. In the ionic exchange of Na₂SO₄ and BaCl₂, which ion from BaCl₂ combines with SO₄²⁻?
Ba²⁺Barium chloride provides Ba²⁺ and Cl⁻ ions. The Ba²⁺ ion combines with SO₄²⁻ from sodium sulphate to form insoluble BaSO₄.
Q44. What is the colour of ferrous sulphate crystals before heating?
GreenHydrated ferrous sulphate (FeSO₄·7H₂O) has a characteristic pale green colour due to the presence of water of crystallization.
Q45. What does the arrow with “Heat” written above it in a chemical equation indicate?
The reaction requires heating to proceed.The “Heat” symbol above the arrow means that the reaction needs to be supplied with heat energy (it is endothermic and requires activation energy).
Q46. What is the main industrial use of the decomposition reaction of calcium carbonate?
To make cementThe cement industry relies on the thermal decomposition of CaCO₃ to CaO, which is then combined with clay and other materials to produce cement.
Q47. What is the specific term for the decomposition reaction carried out using electricity, as shown with water?
Electrolytic DecompositionWhen electrical energy is used to decompose a compound (like water into H₂ and O₂), it is called electrolytic decomposition or electrolysis.
Q48. What is the other name for a double displacement reaction that produces a precipitate?
PrecipitationA precipitation reaction is a specific type of double displacement reaction where one of the products is an insoluble solid (precipitate).
Q49. In the decomposition of ferrous sulphate, what is the fate of the water molecules in the crystal?
They are released as water vapour initially.On gentle heating, hydrated ferrous sulphate (FeSO₄·7H₂O) loses its 7 water molecules as steam, turning from green to white anhydrous FeSO₄.
Q50. What fundamental principle do decomposition reactions demonstrate?
A compound can be broken into its constituent elements or simpler compounds.Decomposition reactions are the reverse of combination reactions. They show that a single compound can be broken down into two or more simpler substances (elements or compounds) by supplying energy.