Acids, Bases and Salts

Sodium chloride is the commonly available salt and so is called common salt. Seawater is the main source of sodium chloride. Seawater contains about 3.5% of soluble salts, the most common of which is sodium chloride (2.7 to 2.9%). Saline water of inland lakes is also a good source of this salt. Sodium chloride is also found as rock salt.

Common salt is generally obtained by evaporation of seawater. In India the coastal line of Gujarat is one of the important areas producing salt by solar evaporation. The hot, dry, windy climate leads to fast evaporation of water from the artificial ponds containing sea water. Crude sodium chloride is obtained by crystallization of 'brine' that contains sodium sulphate, calcium sulphate, calcium chloride and magnesium chloride as impurities.

Pure sodium chloride is obtained from the crude salt by dissolving it in minimum amount of water and filtering it to remove insoluble impurities. The solution is then saturated with hydrogen chloride gas, when crystals of pure sodium chloride separate out. Calcium and magnesium chlorides, being more soluble than sodium chloride, remain in solution.

Properties

• Sodium chloride is a white crystalline solid having a density of 2.17 g/mL
• It melts at 1080 K (807°C) and boils at 1713 K (1440°C)
• It is soluble in water and its solubility is 36 g per 100 g of water at 273 K (0°C). The solubility in water remains constant with temperature
• Pure sodium chloride is non-hygroscopic, but behaves as hygroscopic due to the impurities of CaCl₂ and MgCl₂ in it
• Solid Sodium chloride does not conduct electricity at room temperature but molten sodium chloride is a very good ionic conductor

Uses

• As table salt, an essential constituent of our food
• In the manufacture of Na₂CO₃, NaOH, Cl₂, etc
• For salting out soap, and organic dyes
• In freezing mixtures
• In tanning and textile industries
• As a preservative for fish, meat, butter etc