Chemical Reactions and Equations 

CBSE extra question 

class 10



ONE MARK QUESTIONS



1. In electrolysis of water, why is the volume of gas collected over one electrode double that of gas ?
Ans : Water contains hydrogen and oxygen in the ratio of  2 : 1, that is why volume of Hydrogen is double than that of oxygen collected over the other electrode.

2. What can be seen when a strip of copper metal is placed in a solution of silver nitrate? 
Ans :The solution will become blue, shiny silver metal will get deposited.
Cu(s) + 2AgNO (aq) $Cu(NO ) (aq) + 2Ag(s)

3. State one industrial application of reduction process.
Ans :It is used in the extraction of metals e.g.,
ZnO(s) + C(s) Zn(s) + CO (g)

4. Which one of the following is a chemical change? Give reason also.
(a) Burning of wax (b) Melting of wax
Ans :Burning of gas is a chemical change because new
products with new properties will be formed on burning.

5. Which one is a chemical change: Rusting of iron or melting of iron?
Ans :Rusting of iron is a chemical change. 

6. 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, new substance(s) with new properties is/are formed.

7. Name the oxidising and reducing agent in the following reaction:
CuO + H $Cu+ H O
 Ans : is oxidising agent H is reducing agent.

8.Name and state the law which is kept in mind when we balance chemical equations.
Ans :Law of conservation of mass. It states Matter can neither be created nor be destroyed. The total mass of reactants must be equal to total mass of products.

9. What is meant by a chemical reaction?
Ans :Chemical reaction, a process in which one or more substances, the reactants, are converted to one or more different substances, the products. Substances are either chemical elements or compounds. A chemical reaction rearranges the constituent atoms of the reactants to create different substances as products

 10. AgNO (aq) + NaCl(aq) $AgCl . + NaNO (aq) FeS + H SO $FeSO +H S -
Consider the above mentioned two chemical equations with two different kinds of arrows (- and . ) along with the product. What do these two different arrows indicate?
Ans :shows evolution of gas, . represents a precipitate.

 11.Hydrogen being a highly inflammable gas and oxygen being a supporter of combustion, yet water, a compound made up of hydrogen and oxygen is used to extinguish fire. Why?
Ans :H O is a compound constituted of hydrogen of oxygen
elements and being a compound it has different properties as compared to its constituting elements.

 12.N (g) + 3H (g) $2NH (g), name the type of reaction.
Ans :Combination reaction.

 13.If copper metal is heated over a flame it develops a coating. What is the colour and composition of coating?
Ans : Black coloured coating is formed. It is a due to formation of copper oxide.

 14.Write a balanced chemical equation to represent the following reaction: carbon monoxide reacts with hydrogen gas at 340 atm to form methyl alcohol.
 Ans :CO(g) + 2H (g) CH OH(l)


15.Which one is a chemical change: fermentation of fruit juice or diluting fruit juice?
Ans :Fermentation of fruit juice is a chemical change. 

16.Is burning of a candle wax a physical or a chemical change?
Ans :burning of a candle wax is a chemical change.

17.Write a balanced equation for the chemical reaction that can be characterised as precipitation reaction.
Ans : (aq) + NaCl(aq) $AgCl(s) + NaNO (aq)
 It is a precipitation reaction.

18.State the main difference between endothermic reaction and an exothermic reaction.
 Ans :In endothermic reaction, heat is absorbed. In exothermic reaction, heat is evolved.

19.What happens chemically when quick lime is added to water filled in a bucket?
 Ans :Calcium hydroxide (Slaked lime) is formed with evolution of heat and hissing sound. 
CaO(s) + H2O(l) $Ca(OH) (aq)

20.Define oxidation and reduction.
Ans :Oxidation is a process in which oxygen is added or loss of electrons take place. Reduction is a process in which hydrogen is added or gain of electrons takes place.