SOME IMPORTANT COMPOUNDS OF SODIUM

1. Sodium Chloride, Common Salt or Table Salt [NaCI]

Sea water contains 2.7 to 2.9%by mass of the salt. Sodium chloride is obtained by evaporation of sea water but due to the presence of impurities like CaCl2 and MgCl2 it has deliquescens nature. It is purified by passing HCI gas through the impure saturated solution of
NaCl and due to common ion effect, pure NaCl gets precipitated. 28% NaCl solution is called brine.

2. Sodium Hydroxide or Caustic Soda [NaOH]

Methods of preparation

(i) A 10% solution of Na2CO3 is treated with milk of lime (Causticizing process).

Na2CO3 + Ca(OH)2 → CaCO3 ↓ + 2NaOH

(ii) Electrolytic process involves Nelson cell and Castner-Kellner cell.

A brine solution is electrolysed using a mercury cathode and a carbon anode. Sodium metal discharged at the cathode combines with Hg to form Na-amalgam. Chlorine gas is evolved at the anode.

The amalgam is treated with water to give sodium hydroxide and hydrogen gas.

2Na-Hg + 2H2O → 2NaOH + 2Hg + H2

Physical properties

Sodium hydroxide is a white translucent solid. It is readily soluble in water. Crystals of NaOH are deliquescent.

Chemical properties

1. It is a hygroscopic, deliquescent white solid, absorbs CO2 and moisture from the atmosphere

3. Sodium Carbonate or Washing Soda (Na2CO3 . 10H2O)

Solvay process

CO2 gas is passed through a brine solution saturated with NH3

Sodium bicarbonate is filtered and dried. It is ignited to give sodium carbonate.

Properties

1. Sodium carbonate crystallises from water as decahydrate which effloresces on exposure to dry air forming monohydrate which on heating change to anhydrous salt (soda-ash).

Uses

1. It is used in water softening, laundering and cleaning.
2. It is used in paper, paints and textile industries

4. Sodium Bicarbonate or Baking Soda (NaHCO3) Preparation

It is obtained as an intermediate product in Solvay process.

Properties

Uses

1. It is used as a constituent of baking powder which is a mixture of sodium bicarbonate, starch and potassium bitartrate or cream of tartar and in medicine to remove acidity of the stomach (as antacid).
2. NaHCO3 is a mild antiseptic for skin infections.
3 It is used in fire extinguisher.

5. Microcosmic salts [Na(NH4)HPO4 . 4H2O]

Preparation

It is prepared by dissolving Na2HPO4 and NH4Cl in the molecular proportions in hot water followed by crystallisation.

Properties

On heating it forms a transparent glassy bead of metaphosphate, which gives coloured beads of orthophosphates when heated with coloured salts like that of transition metal ions(Cu2+, Fe2+, Mn2+, Ni2+, CO2+).

This test is called microcosmic bead test.

Na(NH4) HPO4 → NH3 + H2O + NaPO3

sodium metaphosphate

CUSO4 → CuO + SO3

CuO + NaPO3 → CuNaPO4 (blue bead)

It is especially used to detect silica which being insoluble in NaPO3 gives a cloudy bead.