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Q1. The process in which a substance undergoes a change in its physical properties without forming a new substance is called:
A physical change is a change in which the substance’s physical properties (like shape, size, state) change, but no new substance is formed. The original substance can be recovered. Chemical changes involve the formation of new substances. Rusting and burning are chemical changes.
Q2. Which of the following is an example of a chemical change?
Ripening of a fruit is a chemical change because new substances are formed inside the fruit, changing its colour, taste, and texture. Melting wax, breaking glass, and freezing water are physical changes—no new substances are formed.
Q3. When iron nails are placed in a blue copper sulphate solution, the colour of the solution changes from blue to:
Iron is more reactive than copper and displaces copper from copper sulphate solution. The blue colour fades and turns green due to the formation of iron sulphate (FeSO₄). The green colour is characteristic of ferrous ions in solution.
Q4. The reaction between iron and copper sulphate solution is an example of:
In this reaction, iron (more reactive) displaces copper (less reactive) from copper sulphate solution. This is a displacement reaction. The general equation is: Fe + CuSO₄ → FeSO₄ + Cu.
Q5. Which of the following is NOT a characteristic of a chemical change?
In a chemical change, energy is either absorbed or released (as heat, light, etc.). Mass is conserved, but energy change is a key feature. Formation of a new substance, irreversibility (usually), and changes in colour/temperature/gas evolution are all characteristics of chemical changes.
Q6. Burning of a candle involves:
Burning of a candle involves both changes. Melting of wax is a physical change (solid to liquid). Burning of the wick and wax vapour is a chemical change (combustion), producing new substances like carbon dioxide, water vapour, and soot.
Q7. The chemical formula of copper sulphate is:
Copper sulphate has the chemical formula CuSO₄. CuSO₃ is copper sulphite, CuCl₂ is copper chloride, and CuO is copper oxide. The correct formula for copper sulphate is CuSO₄.
Q8. Which gas is produced when vinegar (acetic acid) reacts with baking soda (sodium bicarbonate)?
When vinegar (acetic acid) reacts with baking soda (sodium bicarbonate), carbon dioxide gas is produced. This is the gas that causes the bubbling and fizzing. The reaction is: CH₃COOH + NaHCO₃ → CH₃COONa + H₂O + CO₂.
Q9. Rusting of iron is a chemical change because:
Rusting is a chemical change because a new substance, iron oxide (rust), is formed. Iron reacts with oxygen and moisture to form rust. The properties of rust are completely different from iron. The formation of a new substance is the key indicator.
Q10. Which of the following is an example of a reversible physical change?
Melting of ice is a reversible physical change because ice can be frozen again to form ice. Cooking rice, souring milk, and burning paper are irreversible chemical changes. Reversible changes allow the original substance to be recovered.
Q11. The colour of iron sulphate solution is:
Iron sulphate solution is green in colour. This is due to the presence of ferrous ions (Fe²⁺) in the solution. Copper sulphate solution is blue. The green colour is characteristic of iron(II) salts.
Q12. Which statement best describes a chemical reaction?
A chemical reaction is a process in which new substances with new properties are formed. Atoms are not destroyed; they are rearranged. State changes are physical changes. Energy changes always occur in chemical reactions.
Q13. When magnesium ribbon is burnt in air, it forms:
When magnesium burns in air, it combines with oxygen to form magnesium oxide (MgO), a white powdery ash. The reaction is: 2Mg + O₂ → 2MgO. The bright white flame is characteristic of this reaction.
Q14. The formula of iron sulphate formed in the reaction between iron and copper sulphate is:
Iron reacts with copper sulphate to form iron sulphate (FeSO₄) and copper. The reaction is: Fe + CuSO₄ → FeSO₄ + Cu. FeSO₃ is iron sulphite, Fe₂(SO₄)₃ is iron(III) sulphate, and FeS is iron sulphide.
Q15. Which of the following is a chemical change?
Digestion of food is a chemical change because complex food molecules are broken down into simpler substances by enzymes. Crushing, stretching, and cutting are physical changes—no new substances are formed.
Q16. The brown coating that appears on an iron nail placed in copper sulphate solution is:
The brown coating on the iron nail is copper metal deposited on the nail. Iron displaces copper from the copper sulphate solution, and copper is deposited on the nail as a reddish-brown layer. The reaction is: Fe + CuSO₄ → FeSO₄ + Cu.
Q17. Which of the following changes can be reversed?
Boiling water into steam is a reversible physical change because steam can be condensed back to water. Milk turning into curd, grapes fermenting into wine, and wood burning into ash are irreversible chemical changes.
Q18. In the reaction between iron and copper sulphate, iron acts as:
In this reaction, iron (Fe) loses electrons and is oxidised, while copper ions (Cu²⁺) gain electrons and are reduced. Since iron causes reduction of copper ions, it acts as a reducing agent. It also displaces copper.
Q19. Which of the following is an example of a chemical change that occurs in the kitchen?
Baking a cake is a chemical change because heat causes chemical reactions (like the rising of dough and browning of crust) that produce new substances with different properties. Cutting, grinding, and mixing are physical changes.
Q20. The balanced chemical equation for the reaction between iron and copper sulphate is:
The correct balanced equation is Fe + CuSO₄ → FeSO₄ + Cu. This shows that one atom of iron displaces one atom of copper. Option B is unbalanced, option C has incorrect formulas, and option D is incorrect because the reaction does occur.
Q21. Which of the following is a physical change?
Evaporation of water is a physical change because it involves a change of state from liquid to gas. No new substance is formed. Formation of curd, burning of coal, and photosynthesis are chemical changes.
Q22. The green colour of the solution after iron reacts with copper sulphate is due to the formation of:
The green colour is due to the formation of iron sulphate (FeSO₄) in the solution. Copper sulphate is blue, copper oxide is black, and iron oxide is rust-coloured. Iron sulphate gives the green colour.
Q23. Which of the following is NOT a chemical change?
Breaking a glass tumbler is a physical change because it only changes the shape and size of the glass. No new substance is formed. Souring, rotting, and burning are chemical changes that produce new substances.
Q24. During a chemical change, the total mass of the reactants compared to the total mass of the products is:
According to the Law of Conservation of Mass, mass is neither created nor destroyed in a chemical reaction. The total mass of reactants is always equal to the total mass of products. This is a fundamental principle of chemistry.
Q25. Which metal is more reactive, iron or copper?
Iron is more reactive than copper. This is why iron can displace copper from copper sulphate solution. The reactivity series places iron above copper. Copper is less reactive and cannot displace iron.
Q26. Which of the following changes is accompanied by the release of heat and light?
Burning of a matchstick is a chemical change (combustion) that releases heat and light. Melting, freezing, and dissolving are physical changes that do not typically release light and are usually endothermic or exothermic without light.
Q27. The blue colour of copper sulphate solution is due to:
The blue colour of copper sulphate crystals and solution is due to the presence of water of crystallisation (CuSO₄·5H₂O). When anhydrous copper sulphate (white) is dissolved in water, it becomes blue as it absorbs water. The copper ions also contribute to the colour.
Q28. Which of the following is a characteristic of a physical change?
In a physical change, no new substance is formed. The substance changes its physical state or appearance but retains its chemical identity. Chemical changes form new substances. Physical changes are often reversible.
Q29. What happens when a piece of zinc is added to copper sulphate solution?
Zinc is more reactive than copper and displaces copper from copper sulphate solution. The solution turns green due to formation of zinc sulphate, and a brown coating of copper is deposited on the zinc. The reaction is: Zn + CuSO₄ → ZnSO₄ + Cu.
Q30. Which of the following is an example of a chemical change that occurs during photosynthesis?
Photosynthesis is a chemical change because new substances (glucose and oxygen) are formed from carbon dioxide and water. The other options are physical or physiological processes, not chemical changes.
Q31. The process of a solid changing directly into gas without becoming liquid is called:
Sublimation is the process where a solid directly changes into a gas without passing through the liquid state. Examples include dry ice (solid CO₂) and camphor. Evaporation is liquid to gas, condensation is gas to liquid, and melting is solid to liquid.
Q32. Which of the following is a chemical change?
Burning of wood is a chemical change because it produces new substances like ash, carbon dioxide, and water vapour. Dissolving salt, stretching a spring, and cutting an apple are physical changes.
Q33. In the reaction between iron and copper sulphate, the colour of the iron nail changes to:
The iron nail develops a reddish-brown coating because copper is deposited on it. Copper is reddish-brown in colour. The nail itself may also show some corrosion, but the visible coating is the reddish-brown copper deposit.
Q34. Which of the following is an irreversible change?
Frying an egg is irreversible because the egg white and yolk change chemically and cannot be turned back. Melting chocolate, inflating a balloon, and dissolving sugar are reversible physical changes.
Q35. The reaction in which a single substance breaks down into two or more simpler substances is called:
A decomposition reaction is one in which a single compound breaks down into two or more simpler substances. Displacement involves one element displacing another, combination is the joining of substances, and a physical change is not a chemical reaction.
Q36. Which of the following is a chemical change that happens very slowly?
Rusting is a slow chemical change that takes place over a long period. Bursting a cracker is fast (explosion), burning a candle is moderate, and boiling milk is a physical change (though it can lead to chemical changes if overheated).
Q37. The chemical name of the green substance formed on copper objects when they react with air and moisture is:
The green coating on copper objects is basic copper carbonate (CuCO₃·Cu(OH)₂). It forms when copper reacts with oxygen, carbon dioxide, and moisture in the air. Copper oxide is black, copper carbonate is not the exact compound, and copper sulphate is blue.
Q38. Which of the following statements about the reaction between iron and copper sulphate is correct?
In this reaction, iron (which goes into solution as Fe²⁺) loses mass as it dissolves. Copper ions gain electrons and deposit as copper metal on the nail, so copper gains mass. This is a displacement reaction.
Q39. Which of the following is an example of a physical change that is not easily reversible?
Breaking a glass is a physical change (no new substance is formed), but it is not easily reversible because the broken pieces cannot be rejoined to form the original glass. Freezing, melting, and dissolving are reversible.
Q40. What is the colour of anhydrous copper sulphate (without water)?
Anhydrous copper sulphate (CuSO₄) is white. It turns blue when water is added and it becomes hydrated (CuSO₄·5H₂O). This is a test for the presence of water. The blue colour is due to water of crystallisation.
Q41. The energy change that occurs in most chemical reactions is in the form of:
Chemical reactions can release or absorb energy in various forms: heat (exothermic/endothermic), light (burning), sound (explosions), and electricity (batteries). The form of energy depends on the reaction.
Q42. Which of the following is a chemical change that occurs in plants?
The conversion of starch into glucose is a chemical change because new substances are formed. Transport of water, transpiration, and stomatal movement are physical processes.
Q43. The brown gas evolved when copper nitrate is heated is:
When copper nitrate is heated, it decomposes to give copper oxide, oxygen, and nitrogen dioxide (NO₂), a reddish-brown gas with a pungent smell. Oxygen is colourless, hydrogen is colourless, and carbon dioxide is also colourless.
Q44. Which of the following is an example of a chemical change that produces a gas?
Adding baking soda to vinegar produces carbon dioxide gas (bubbling). Boiling water, sublimation of camphor, and freezing juice are physical changes that do not produce a new gas. The reaction is: NaHCO₃ + CH₃COOH → CO₂ + H₂O + CH₃COONa.
Q45. The type of change in which the original substance can be obtained back by physical methods is called:
A reversible physical change is one where the original substance can be recovered by physical methods, such as melting, freezing, or dissolving. Chemical changes are usually irreversible. Periodic changes repeat at regular intervals.
Q46. When iron nails are placed in copper sulphate solution, the temperature of the solution:
The reaction between iron and copper sulphate is exothermic, meaning it releases heat. Therefore, the temperature of the solution increases slightly. This is a displacement reaction that releases energy.
Q47. Which of the following is a chemical change that is useful in everyday life?
Cooking of food is a chemical change that breaks down complex substances into simpler, digestible forms. It is useful in daily life. Drying, sharpening, and folding are physical changes.
Q48. The black coating formed on silver jewellery over time is due to reaction with:
Silver reacts with hydrogen sulphide (H₂S) present in air to form silver sulphide (Ag₂S), which is black. This tarnishing is a chemical change. Oxygen, carbon dioxide, and nitrogen do not cause this black coating.
Q49. Which of the following is an example of a physical change involving change of state only?
Condensation is a physical change involving a change of state from gas to liquid. No new substance is formed. Burning, ripening, and germination are chemical changes that produce new substances.
Q50. In the reaction between iron and copper sulphate, what is the colour change observed in the solution?
The copper sulphate solution is initially blue. As iron displaces copper, the solution turns green due to the formation of iron sulphate (FeSO₄). The blue colour fades and green appears. The solution does not become colourless, red, or start from colourless.