1. Which one is a chemical change-rusting of iron or melting of iron?
Ans: Rusting of iron.
2. Name and state the law which is kept in mind while we balance a chemical equation
Ans: Law of conservation of mass: Mass can neither be created nor be destroyed during a chemical reaction.
3. State one basic difference between a physical change and a chemical change.
Ans: In a physical change, no new substance is formed. In a chemical change, a new substance is formed.
4. What happens when quicklime is added to water?
Ans: Quicklime reacts with water vigorously to produce slaked lime and a large amount of heat is liberated.
CaO (s) + H2O → Ca (OH)2 + Heat
Quick Lime slaked Lime
5. What happens when ZnCO3 is heated in the absence of air? Give the relevant equation
Ans: ZnO(s) and CO (g) are formed.
6. Is burning of a candle, a physical change or a chemical change?
Ans: Both, chemical change and physical change.
7. Write the chemical equation for reactions that take place when lead nitrate and potassium iodide solutions are mixed
8. Write a balanced chemical equation:
Ans: Balanced equation is
9. Which one is the chemical change – Fermentation of fruit juice or diluting fruit juice?
Ans: Fermentation of fruit juice.
10. What is meant by the skeletal equation?
Ans: An unbalanced equation is called a skeletal equation.
11. What is observed when carbon dioxide gas is passed through lime water?
(i) For a short duration?
(ii) For long duration?
Also, write the chemical equations for the reaction involved.
(i) Limewater turns milky due to the formation of CaCO3, which is insoluble in water.
(ii) A clear solution is obtained due to the formation of calcium bicarbonate.
Ca (HCO3) which is soluble in water
12. Why do we store silver chloride in dark colored bottles? Explain in brief.
Ans: Silver chloride on exposure to sunlight undergoes photolytic decomposition.
Therefore it is stored in dark colored bottles.
13. Define a combination reaction. Give one example of a combination reaction which is also exothermic.
Ans: A combination reaction is said to have occurred when two or more than two substances combine to form a single substance.
14: What happen chemically when quicklime is added to water filled in a bucket?
Ans. Quick lime react with water to form slaked lime and produces lot of heat and hissing sound.
CaO + H2O → Ca(OH)2 + heat + hissing sound