Question 1.
What is a balanced chemical equation? Why should chemical equations be balanced? (AS1)

Ans:-In a reaction, if both side molecules are the same number then the reaction is called a balanced chemical reaction. According to the Conservation of mass states that in a reaction the mass of reactants and products must be the same. So chemical reactions always are balanced.

Question 2.
Balance the following chemical equations. (AS1)

(a) NaOH + H2SO4 -> Na2SO4 + H2O

(b) Hg (NO3)2 + KI -> HgI2 +KNO3

(c) H2 + O2 -> H2O

(d) KClO3 -> KCl + O2

(e) C3H8 + O2 -> CO2+ H2O


(a) 2 NaOH +H2SO4 -> Na2SO4 + H2O

(b) Hg (NO3)2 + 2KI -> HgI2 + 2KNO3

(c) 2H2 + O2 -> 2H2O

(d) 2 KClO3 -> 2KCl + 3O2

(e) C3H8 + 5O2 -> 3CO2 + 4 H2O

Question 3.
Write the balanced chemical equations for the following reactions. (AS1)

(a) Zinc + Silver nitrate -> Zinc nitrate + Silver.

(b) Aluminium + copper chloride -> Aluminium chloride + Copper.

(c) Hydrogen + Chlorine. ->Hydrogen chloride.


(a) Zn + 2Ag (NO3) ->Zn (NO3)2 + 2Ag

(b) 2Al + 3CuCl2 -> 2AlCl3 + 3Cu

(c) H2 + Cl2 -> 2HCl

Question 4.
Write the balanced chemical equation for the following and identifythe type of reaction in each case. (ASI)

(a) Calcium hydroxide (aq) + Nitric acid (aq) -> Water (l) + Calcium nitrate (aq)

(b) Magnesium (s) + Iodine (g) -> Magnesium Iodide. (s)

(c) Magnesium(s) + Hydrochloric acid (aq) -> Magnesium chloride (aq) + Hydrogen (g)

(d) Zinc(s) + Calcium chloride (aq) -> Zinc Chloride (aq) + Ca(s)


(a) Ca (OH) 2(aq) + 2HNO3 (aq) ->2H2O (l) + Ca (NO3)2(aq)

(b) Mg(s) + I2(s) -> MgI2(s)

(c) Mg(s) + 2HCl (aq) ->MgCI2 (aq) + H2 (g)

(d) Zn(s) + CaCl2 (aq) ->ZnCl2 (aq) + Ca(s)

Question 5.
Write an equation for decomposition reaction where energy is supplied in the form of heat/light / electricity. (AS1)

Ans:The decomposition reaction is, 2AgCl -> 2Ag + Cl2.

Question 6.
What do you mean by precipitation reaction? (AS1)

Ans:-In a reaction where an insoluble and soluble solution be made by reacting of two aqueous solution compounds is called a precipitation reaction.

Question 7.
Name the reactions taking place in the presence of sunlight? (AS1)

Ans:Photochemical reaction taking place in the presence of sunlight.

Question 8.
Why does respiration considered as an exothermic reaction? Explain. (AS1)

Ans:As a result of respiration some amount of heat is produced in our body. In an exothermic reaction, heat produces so compared to this reaction respiration is called an exothermic reaction.

Question 9.
What is the difference between displacement and double displacement reactions? Write equations for these reactions? (AS1)


Displacement reaction Double displacement


Less reactive elementdisplaces by more reactiveelements

There is a mutual exchange ofion in between the element
Fe + CuSO4 -> FeSO4 + Cu

Ag(NO3) + NaCl -> AgCl +


Question 10.
MnO2 + 4HCl -> MnCl2 + 2H2O + Cl2
In the above equation, name the compound which is oxidized and which is reduced? (AS1)

Ans: The compound which is oxidized is HCl. The compound which is reduced is MnO2.

Question 11.
Give two examples for oxidation-reduction reaction. (AS1)

Ans: Example,

(1) Mg + Zn (NO3)2 -> Zn + Mg (NO3)2

(2) Na2 + Cl2 -> 2NaCl

Question 12.
In the refining of silver, the recovery of silver from silver nitrate solution involved displacement by copper metal. Write the reaction involved. (AS1)

Ans: The reaction is 2Ag (NO3)2 + Cu -> 2Ag + Cu (NO3)2

Question 13.
What do you mean by corrosion? How can you prevent it? (AS1)

Ans: In the presence of moisture in the air the metal react with it.This phenomenon is called corrosion. The corrosion will be prevented if we use alloy or by galvanization or by painting on the surface etc.

Question 14.
Explain rancidity. (AS1)

Ans: If oil is used many times it reacts with moisture present in the water and became rancid. This type of oxidation of oil or others is called rancidity.

Question 15.
Balance the following chemical equation including the physical states. (AS1)

(a) C6H12O6 --------> C2H5OH + CO2

(b) Fe + O2 --------> Fe2O3

(c) NH3 + Cl2 --------> N2H4+NH4Cl

(d) Na + H2O --------> NaOH + H2


(a) C6H1206 ->2C2H5 (OH) + + 2 CO2

(b) 4Fe + 3O2 -> 2Fe2O3

(c) 4NH3 + Cl2 -> N2H4 + 2NH4Cl

(d) 2Na + 2 H2O -> 2NaOH + H2

Question 16.
Balance the chemical equation by including the physical states of the substances for the following reactions. (AS1)

(a) Barium chloride and sodium sulphate aqueous solutions react to give insoluble Barium sulphate and aqueous solution of sodium chloride.

Ans: BaCl2 (aq) + Na2SO4 (aq) -> BaSO4(s) + NaCl (aq)

In the above reaction barium chloride when react with sodium sulphate it produces solid barium sulphate and salt.

(b) Sodium hydroxide reacts with hydrochloric acid to produce sodium chloride and water.

Ans: An acid and base when react always produce salt and water. In this reaction of NaOH and HCl the product is salt of NaCl and H2O.

NaOH + HCl -> NaCl + H2O

(c) Zinc pieces react with dilute hydrochloric acid to liberate hydrogen gas and forms zinc chloride.

Ans: Zn(s) + 2HCl (aq) ->ZnCl2 (aq) + H2 (g)

After reacting with hydrochloric acid zinc pieces produce zinc chloride solution and hydrogen.

Question 17.
A shiny brown coloured element ‘X’ on heating in the air becomes black in colour. Can you predict the element ‘X’ and the black coloured substance formed? How do you support your predictions? (AS2)

Ans: As we know that copper in presence of oxygen after heating becomes black. So the X element must be copper and the black colour substance is copper oxide. 2Cu (brown) + O2->2CuO (black).

Question 18.
Why do we apply paint on iron articles? (AS7)

Ans: As in the presence of moisture in air iron react with it. So to protect it from rusting we apply paint on iron articles.

Question 19.
What is the use of keeping food in airtight containers? (AS7)

Ans: If we kept food outside for some time it started oxidation. So to reduce oxidation of food is always are kept in airtight container and it will be safe in that.

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