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Acids, Bases and Salts - Preparation and uses of Sodium Hydroxide, Bleaching powder, Baking soda, Washing soda and Plaster of Paris

Grade 10CBSE

Review the key concepts, formulae, and examples before starting your quiz.

πŸ”‘Concepts

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Sodium Hydroxide (NaOHNaOH): Produced by the Chlor-alkali process through the electrolysis of aqueous sodium chloride (brine). Chlorine gas is released at the anode, hydrogen gas at the cathode, and NaOHNaOH solution is formed near the cathode.

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Bleaching Powder (CaOCl2CaOCl_2): Formed by the action of chlorine gas on dry slaked lime (Ca(OH)2Ca(OH)_2). It is used as a bleaching agent in textiles and as a disinfectant for drinking water.

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Baking Soda (NaHCO3NaHCO_3): Chemically called Sodium Hydrogen Carbonate. It is produced using the Solvay process involving NaClNaCl, H2OH_2O, CO2CO_2, and NH3NH_3. It is a mild, non-corrosive basic salt used in baking and as an antacid.

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Washing Soda (Na2CO3β‹…10H2ONa_2CO_3 \cdot 10H_2O): Obtained by the recrystallization of sodium carbonate. It is used in glass, soap, and paper industries and for removing the permanent hardness of water.

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Plaster of Paris (CaSO4β‹…12H2OCaSO_4 \cdot \frac{1}{2}H_2O): Calcium sulphate hemihydrate obtained by heating Gypsum (CaSO4β‹…2H2OCaSO_4 \cdot 2H_2O) at 373Β K373\text{ K}. It turns back into Gypsum on mixing with water, forming a hard solid mass.

πŸ“Formulae

2NaCl(aq)+2H2O(l)β†’electrolysis2NaOH(aq)+Cl2(g)+H2(g)2NaCl(aq) + 2H_2O(l) \xrightarrow{\text{electrolysis}} 2NaOH(aq) + Cl_2(g) + H_2(g)

Ca(OH)2+Cl2β†’CaOCl2+H2OCa(OH)_2 + Cl_2 \rightarrow CaOCl_2 + H_2O

NaCl+H2O+CO2+NH3β†’NH4Cl+NaHCO3NaCl + H_2O + CO_2 + NH_3 \rightarrow NH_4Cl + NaHCO_3

2NaHCO3β†’Ξ”Na2CO3+H2O+CO22NaHCO_3 \xrightarrow{\Delta} Na_2CO_3 + H_2O + CO_2

Na2CO3+10H2O→Na2CO3⋅10H2ONa_2CO_3 + 10H_2O \rightarrow Na_2CO_3 \cdot 10H_2O

CaSO4⋅2H2O→373 KCaSO4⋅12H2O+112H2OCaSO_4 \cdot 2H_2O \xrightarrow{373\text{ K}} CaSO_4 \cdot \frac{1}{2}H_2O + 1\frac{1}{2}H_2O

πŸ’‘Examples

Problem 1:

Why should Plaster of Paris be stored in a moisture-proof container?

Solution:

Plaster of Paris (CaSO4β‹…12H2OCaSO_4 \cdot \frac{1}{2}H_2O) is a hygroscopic substance. In the presence of moisture, it absorbs water to form Gypsum (CaSO4β‹…2H2OCaSO_4 \cdot 2H_2O), which is a hard solid mass, making the plaster useless for further application.

Explanation:

The chemical reaction involved is: CaSO4⋅12H2O+112H2O→CaSO4⋅2H2OCaSO_4 \cdot \frac{1}{2}H_2O + 1\frac{1}{2}H_2O \rightarrow CaSO_4 \cdot 2H_2O

Problem 2:

What happens when a solution of sodium hydrogen carbonate is heated? Write the equation.

Solution:

When sodium hydrogen carbonate (NaHCO3NaHCO_3) is heated, it decomposes to form sodium carbonate (Na2CO3Na_2CO_3), water (H2OH_2O), and carbon dioxide (CO2CO_2).

Explanation:

Equation: 2NaHCO3β†’Ξ”Na2CO3+H2O+CO22NaHCO_3 \xrightarrow{\Delta} Na_2CO_3 + H_2O + CO_2. This CO2CO_2 gas causes bread or cake to rise, making them soft and spongy.

Problem 3:

Identify the compound of calcium which is used for disinfecting drinking water and write its preparation.

Solution:

The compound is Bleaching Powder (CaOCl2CaOCl_2). It is prepared by the action of chlorine gas on dry slaked lime.

Explanation:

Chemical equation: Ca(OH)2+Cl2β†’CaOCl2+H2OCa(OH)_2 + Cl_2 \rightarrow CaOCl_2 + H_2O

Preparation and uses of Sodium Hydroxide, Bleaching powder, Baking soda, Washing soda and Plaster…