Chapter 2: Acids, Bases and Salts

Q43Written answer

In the following schematic diagram for the preparation of hydrogen gas, as shown in Figure 2.3, what would happen if the following changes are made?

preparation of hydrogen gas

(a) In place of zinc granules, the same amount of zinc dust is taken in the test tube

(b) Instead of dilute sulphuric acid, dilute hydrochloric acid is taken

(c) In place of zinc, copper turnings are taken

(d) Sodium hydroxide is taken in place of dilute sulphuric acid, and the tube is heated.

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Worked solution

In place of Zinc granules if we use Zinc dust reaction speed increases
Instead of dilute sulphuric acid if we use dilute hydrochloric acid ZINC Chloride is formed
Zn+ 2HCl→ ZnCl₂+H₂
If we use copper in place of Zinc there will be no reaction as copper will not react with dilute acids
Sodium Zincate is produced if we use NaOH solution in place of acidZn+2NaOH→ Na₂ZnO₂+ H2

Q44Written answer

For making a cake, baking powder is taken. If at home, your mother uses baking soda instead of baking powder in cake,

(a) how will it affect the taste of the cake and why?

(b) how can baking soda be converted into baking powder?

(c) what is the role of tartaric acid added to baking soda?

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a) If we use baking soda instead of baking powder taste of the cake will be bitter. Upon heating baking, soda sodium carbonate will be formed, which will make the cake taste bitter.

2NaHCO₃ +Heat Na₂Co₃+CO2+H₂O

b) Baking soda can be converted into baking powder by adding an edible weak acid like tartaric acid.

c) When tartaric acid is dissolved in water, it gives out Hydrogen ions. Hydrogen ions react with Sodium Carbonate to produce carbon dioxide, which will make the cake fluffy.

Q45Written answer

A metal carbonate X on reacting with acid gives a gas which when passed through a solution Y gives the carbonate back. On the other hand, a gas G that is obtained at the anode during electrolysis of brine is passed on dry Y, and it gives a compound Z, used for disinfecting drinking water. Identity X, Y, G and Z.

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Worked solution

X is Calcium. When calcium carbonate reacts with HCl, it gives out CO₂ gas.

CaCO₃ + HCl→ CaCl₂+CO₂+H₂O

When CO2 is passed into lime water, it turns milky due to the formation of Calcium carbonate.

Hence, solution Y is lime water

When chlorine gas is passed on dry lime water, it gives bleaching powder which is used for disinfecting water.

Q46Written answer

A dry pellet of a common base B, when kept in the open absorbs moisture and turns sticky. The compound is also a by-product of the chloralkali process. Identify B. What type of reaction occurs when B is treated with an acidic oxide? Write a balanced chemical equation for one such solution.

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Worked solution

A compound which is a byproduct of the chloralkali process is NaOH. Hence compound B is NaOH.

When NaOH is treated with acidic oxide neutralization process occurs. For example, If NaOH is treated with carbon-di-oxide, it gives Sodium carbonate.

2NaOH+ CO2 →Na2CO3+ H2O

Q47Written answer

A sulphate salt of Group 2 element of the Periodic Table is a white, soft substance, which can be moulded into different shapes by making its dough. When this compound is left in the open for some time, it becomes a solid mass and cannot be used for moulding purposes. Identify the sulphate salt, and why does it show such behaviour? Give the reaction involved.

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Worked solution

The sulphate salt should be calcium sulphate which is white and soft substance. Calcium sulphate is popularly known as plaster of Paris.

Plaster of Paris has half molecule of water of crystallization. When we leave plaster of Paris open for some time, it absorbs moisture to gain a number of molecules of crystallization. This newly formed compound is called Gypsum, which is hard to make moulds.

Q48Written answer

Identify the compound X on the basis of the reactions given below. Also, write the name and chemical formulae of A, B and C.

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