Chemical Name: Sodium Chloride

Chemical Formula: NaCl

Uses:

• It is an essential component of our diet and is used in cooking.
• It is used as a food preservative, for example, in curing meat and pickling.
• It is a raw material for the manufacture of many important chemicals like sodium hydroxide, washing soda, and baking soda.

The chlor-alkali process is the process of electrolysis of an aqueous solution of sodium chloride (brine). It is called chlor-alkali because of the products formed: 'chlor' for chlorine and 'alkali' for sodium hydroxide.

Equation: $2NaCl(aq) + 2H_2O(l) \xrightarrow{\text{Electrolysis}} 2NaOH(aq) + Cl_2(g) + H_2(g)$

Products and Uses:

• Sodium Hydroxide (NaOH): Used in the manufacturing of soaps and detergents, paper, and artificial fibers.
• Chlorine (Cl₂): Used for water treatment, in the manufacturing of PVC, and as a disinfectant.
• Hydrogen (H₂): Used as a fuel, in the manufacturing of ammonia for fertilizers, and in the hydrogenation of oils to make margarine.

Chemical Name: Calcium Oxychloride

Chemical Formula: CaOCl₂

Preparation: Bleaching powder is produced by the action of chlorine gas on dry slaked lime (calcium hydroxide).

Equation: $Ca(OH)_2(s) + Cl_2(g) \rightarrow CaOCl_2(s) + H_2O(l)$

Uses:

• For bleaching cotton and linen in the textile industry.
• As an oxidizing agent in many chemical industries.
• For disinfecting drinking water to make it free from germs.

Baking soda is chemically Sodium Hydrogen Carbonate (NaHCO₃).

Preparation: It is prepared using sodium chloride as one of the raw materials (Solvay process):

Equation: $NaCl(aq) + H_2O(l) + CO_2(g) + NH_3(g) \rightarrow NH_4Cl(aq) + NaHCO_3(s)$

Use in Baking Powder: Baking powder is a mixture of baking soda and a mild edible acid like tartaric acid. When baking powder is heated or mixed with water, the baking soda reacts with the acid to produce carbon dioxide gas. This CO₂ gas gets trapped in the wet dough, causing it to rise and making cakes and bread soft and spongy.

Reaction: $NaHCO_3 + H^+ (from\ acid) \rightarrow CO_2 + H_2O + Sodium\ salt\ of\ acid$

Washing soda is chemically Sodium Carbonate Decahydrate (Na₂CO₃·10H₂O).

Obtaining from Baking Soda: Sodium carbonate is first obtained by heating baking soda:

Equation: $2NaHCO_3(s) \xrightarrow{\text{Heat}} Na_2CO_3(s) + H_2O(l) + CO_2(g)$

Then, recrystallization of anhydrous sodium carbonate (soda ash) yields washing soda:

Equation: $Na_2CO_3(s) + 10H_2O(l) \rightarrow Na_2CO_3 \cdot 10H_2O(s)$

Uses:

• In glass, soap, and paper industries.
• As a cleaning agent for domestic purposes.
• For removing permanent hardness of water.

Plaster of Paris (POP) is chemically Calcium Sulphate Hemihydrate (CaSO₄·½H₂O).

Preparation: It is obtained by heating gypsum (CaSO₄·2H₂O) at 373 K (100°C).

Equation: $CaSO_4 \cdot 2H_2O(s) \xrightarrow{373 K} CaSO_4 \cdot \frac{1}{2}H_2O(s) + 1\frac{1}{2}H_2O(l)$

Reason for moisture-proof storage: Plaster of Paris is stored in a moisture-proof container because it is a white powder that readily reacts with moisture (water) to form a hard solid mass of gypsum. This setting property is crucial for its uses (like bone setting, making toys). If it absorbs moisture from the atmosphere, it will lose its setting property and become useless.

Setting Reaction: $CaSO_4 \cdot \frac{1}{2}H_2O(s) + 1\frac{1}{2}H_2O(l) \rightarrow CaSO_4 \cdot 2H_2O(s)$

Soap: Soaps are the sodium or potassium salts of long-chain carboxylic acids (fatty acids).

Cleaning Action of Soap (Micelle Formation):

A soap molecule has two distinct parts:

• Hydrophilic (water-loving) head: This is the ionic (carboxylate) end (-COO⁻Na⁺), which is soluble in water.
• Hydrophobic (water-repelling) tail: This is the long hydrocarbon chain, which is soluble in oil/grease but not in water.

When soap is dissolved in water, the molecules arrange themselves to form a spherical structure called a micelle. The hydrophobic tails point towards the center, away from the water, while the hydrophilic heads point outwards into the water.

When greasy dirt is present on a cloth, the hydrophobic tails of the soap molecules attach themselves to the oil/grease particles. The oil/grease is then trapped in the center of the micelle. These micelles, with the dirt encapsulated, remain suspended in water as a colloid due to the repulsion between the negatively charged hydrophilic heads. When the cloth is rinsed, the micelles, along with the trapped dirt, are washed away, thus cleaning the cloth.

Detergents: Detergents are generally ammonium or sulphonate salts of long-chain carboxylic acids. More precisely, they are long-chain alkyl hydrogen sulphonates or alkyl benzene sulphonates.

Advantages over Soaps:

• Effectiveness in Hard Water: Detergents do not form insoluble precipitates (scum) with calcium (Ca²⁺) and magnesium (Mg²⁺) ions present in hard water. This means they can be used effectively for washing in hard water, unlike soaps which form scum.
• Effectiveness in Acidic Water: Detergents work well even in acidic water, whereas soaps lose their effectiveness in acidic conditions because the fatty acids precipitate out.
• Stronger Cleaning Action: Many detergents have a stronger cleaning action compared to soaps.

Difference between Soap and Detergent:

• Chemical Composition:
  • Soap: Sodium or potassium salts of long-chain fatty acids.
  • Detergent: Sodium salts of long-chain alkyl hydrogen sulphonates or alkyl benzene sulphonates.
• Effectiveness in Hard Water:
  • Soap: Forms insoluble scum (precipitate) with calcium and magnesium ions in hard water, which reduces its cleaning action and leaves a residue.
  • Detergent: Does not form insoluble scum with calcium and magnesium ions in hard water, thus it works effectively in hard water.

Chemical Formula of Gypsum: CaSO₄·2H₂O (Calcium Sulphate Dihydrate)

When gypsum is heated at 373 K (100°C), it loses three-fourths of its water of crystallization and forms Plaster of Paris (Calcium Sulphate Hemihydrate).

Equation: $CaSO_4 \cdot 2H_2O(s) \xrightarrow{373 K} CaSO_4 \cdot \frac{1}{2}H_2O(s) + 1\frac{1}{2}H_2O(l)$