Sunday, 9 August 2015



1.Which of the reactions about the reaction below are incorrect?
a) Lead is getting oxidised
b) Carbon dioxide is getting oxidised
c) Carbon is getting oxidised
d) Lead oxide is getting reduced
 ANSWER- (a)

2. Fe2O3+2Al--->Al2O3+2Fe
The above reaction is an example of a
a) Combination reaction
b) Double displacement reaction
c) Decomposition reaction
d) Displacement reaction

3. What happens when dilute hydrochloric acid is added to iron fillings. Tick the correct answer.
a)  Hydrogen gas and iron chloride is produced
b) Chlorine gas and iron hydroxide are produced
c) No reaction takes place
d) Iron salt and water are produced
ANSWER-: (a)

4. What is balanced chemical equation? Why should chemical equations be balanced?
ANSWER-:The number of atoms of each element remains same before and after reaction is known as balanced chemical equation.
Chemical equations should be balanced so as to satisfy the law of conservation of mass which states that mass can neither be created nor destroyed.

5. Translate the following statements into chemical equations and balance them.
a) Hydrogen gas combines with nitrogen to form ammonia
b) Hydrogen sulphide gas burns in air to give water and sulpher dioxide
c) Barium Chloride reacts with aluminum sulphate to give aluminum chloride and a precipitate of barium sulphate.
d) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas

ANSWER- a)3H2(g)+N2(g)--->2NH3(g)
b)2H2S(g)+3O2(g)--->2H2O(L)+  2SO2(g)
6.Balance the following chemical equations.

ANSWER:-a) 2HNO3+Ca(OH)2--->Ca(NO3)2+
b)2NaOH+H2SO4--->Na2SO4+    2H2O

7.Write the balanced chemical equations for the following reactions.
a)Calcium hydroxide+Carbon dioxide--->Calcium Carbonate+Water
b)Zinc+Silver nitrate--->Zinc nitrate+Silver
c)Aluminium+Copper chloride--->Aluminium Chloride+Copper
d)Barium Chloride+Potassium Sulphate---> Barium Sulphate+Potassium Chloride

ANSWER:-a)Ca(OH)2+CO--->    CaCO3+H2O

8. Write the balanced chemical equation for the following and identify the type of reaction in each case.
a)Potassium bromide(aq)+Barium iodide(aq)--->Potassium iodide(aq)+Barium bromide(s)
b)Zinc carbonate(s)--->zinc oxide(s)+carbon dioxide(g)
c) Hydrogen(g)+Chlorine(g)--->hydrogen chloride(g)
d)Magnesium(s)+Hydrochloric acid(aq)---->Magnesium chloride(aq)+Hydrogen(g)

ANSWER:-a) 2KBr(aq)+BaI2(aq)---> 2KI(aq)+BaBr2(s)

b) ZnCO3(s)--->ZnO(s)+CO2(g)



9)What does one mean by exothermic and endothermic reactions?Give examples.

ANSWER-: Exothermic reaction is the type of chemical reaction
that releases energy by light or heat. Example-Burning of a substance, Neutralization.
Endothermic reaction is the type of reaction that absorbs energy but not always in the form of heat. Example-Melting of an ice, thermal decomposition reactions.

10. Why is respiration considered as an exothermic reaction ? Explain

ANSWER-: Respiration is known as exothermic reaction as because in respiration oxidation of glucose takes place which produces a large amount of heat energy.


11.Why are decomposition reactions called the opposite of combination reactions ?
Write equations for these reactions.

ANSWER:-In a decomposition reaction a single substance decomposes to give two or more substances whereas in combination reaction to or more substance combine to form a single substance .Hence decomposition reaction is called the opposite of combination reaction

12. Write one equation each for decomposition reactions where energy is supplied in the form of heat, light or electricity.

ANSWER:- 1.Heat energy CaCO3--heat-->CaO(s)+   CO2(g)
2.Light enegy:-2AgCl(s)---sunlight-->2Ag(s)+Cl2(g)
3.Electricity 2H2O(l)---electricity-->2H2(g)+O2(g)

13.What is the difference between displacement and double displacement
reactions? Write equations for these reactions.

ANSWER-:When an element displaces another element from its compound displacement reaction occurs whereas in double displacement two  different atoms or group of atoms are exchanged
Displacement-Fe(s)+ CuSO4--->FeSO4(aq)+Cu(s)
Double displacement-Na2SO4 (aq)+BaCl2(aq)--->BaSO4(s)+2NaCl(aq)

14. In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write down the reaction involved.

ANSWER:-Cu(s)+2AgNO3(aq)--->   Cu(NO3)2(aq)+2Ag(s)

15. What do you mean by a precipitation reaction? Explain by giving examples..?

ANSWER:-Precipitation reaction is the type of reaction which produces insoluble salts

BaSO4 is insoluble in water and its a white precipitate

16. Explain the following in terms of gain or loss of oxygen with two examples each.
(a) Oxidation
(b) Reduction

ANSWER:-a) Oxidation- Oxidation is a chemical reaction in which gain of oxygen or loss of hydrogen takes place
b) Reduction-Reduction is a chemical reaction in which loss of oxygen or gain of hydrogen takes place.

17. A shiny brown coloured element X on heating in air becomes black in colour. Write the name the element X and the black coloured compound formed.


Compound formed-Copper Oxide

18.Why do we apply paint on iron articles?

To prevent rusting we apply paint on iron articles as because after painting iron does not come in contact with air and moisture and prevent rusting.

19.Oil and fat containing food items are flushed with nitrogen. Why?

ANSWER:-Nitrogen acts as an oxidized and prevents them from being oxidized so oil and fat containing food items are flushed with nitrogen.

20. Explain the following terms with one example each.
a) corrosion
b) rancidity

ANSWER: Corrosion-:It is the process in which when a metal is attacked by moisture, acids etc and the metal corrodes

b)rancidity:-It is the process in which when the substances containing oils and fat which when exposed to air becomes rancid and their taste and smell changes.
Written By Badal Paul
The author is a passionate blogger, writer and educationalist. This blog is created to ease troubles of the Cbse students. The author holds multiple blogs and the writer of the Novel KALCHAKRA, OOM AND THE CHOSEN FIVE.