Chemical Properties and Uses of Salts

For example, copper sulphate is often found as $\text{CuSO}_4 \cdot 5\text{H}_2\text{O}$ (blue vitriol), where five molecules of water are chemically bonded to the salt.

Common Salt and Sodium Hydroxide

Common Salt ($\text{NaCl}$)

Sodium chloride, or common salt, is perhaps the most widely used salt in the world. It is produced industrially through the chlor-alkali process, which involves the electrolysis of an aqueous solution of sodium chloride (brine).

The chemical equation for this process is: $\begin{aligned} 2\text{NaCl(aq)} + 2\text{H}_2\text{O(l)} &\rightarrow 2\text{NaOH(aq)} + \text{Cl}_2\text{(g)} + \text{H}_2\text{(g)} \end{aligned}$

Common salt is used in daily food consumption, as a preservative, and as a raw material for manufacturing metals like sodium ($\text{Na}$) and gases like chlorine ($\text{Cl}_2$).

Sodium Hydroxide ($\text{NaOH}$)

As seen in the chlor-alkali process, sodium hydroxide (also known as caustic soda) is a major byproduct. It is a strong base and an alkali used extensively in the manufacture of paper, soaps, detergents, and for de-greasing metals.

Bleaching Powder and Baking Soda

Bleaching Powder ($\text{CaOCl}_2$)

Bleaching powder is produced by the action of chlorine gas on dry slaked lime [$\text{Ca(OH)}_2$]. $\text{Cl}_2 + \text{Ca(OH)}_2 \rightarrow \text{CaOCl}_2 + \text{H}_2\text{O}$

It is characterized by a strong smell of chlorine and acts as a powerful oxidizing agent. Its primary uses include bleaching cotton and linen in the textile industry, bleaching wood pulp in paper factories, and disinfecting drinking water.

Baking Soda ($\text{NaHCO}_3$)

Sodium hydrogen carbonate, commonly known as baking soda, is a mild, non-corrosive base. It is an essential ingredient in baking powder (which is a mixture of baking soda and tartaric acid).

When baking soda is heated during cooking, it undergoes thermal decomposition: $\begin{aligned} 2\text{NaHCO}_3 &\xrightarrow{\Delta} \text{Na}_2\text{CO}_3 + \text{H}_2\text{O} + \text{CO}_2 \end{aligned}$

The release of carbon dioxide ($\text{CO}_2$) gas is what causes bread and cakes to rise, making them soft and spongy. Additionally, it is used as an ingredient in antacids and in fire extinguishers.

Washing Soda and Plaster of Paris

Washing Soda ($\text{Na}_2\text{CO}_3 \cdot 10\text{H}_2\text{O}$)

Washing soda is a basic, crystalline salt that contains ten molecules of water of crystallization. It is prepared by the re-crystallization of sodium carbonate.

Washing soda is highly useful in the glass, soap, and paper industries. It is also used for manufacturing borax and is an effective agent for removing the permanent hardness of water.

Plaster of Paris ($\text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O}$)

Plaster of Paris (POP) is a white powder known chemically as calcium sulphate hemihydrate. It is prepared by heating gypsum ($\text{CaSO}_4 \cdot 2\text{H}_2\text{O}$) at a controlled temperature of $373\text{K}$.

$\begin{aligned} \text{CaSO}_4 \cdot 2\text{H}_2\text{O} &\xrightarrow{373\text{K}} \text{CaSO}_4 \cdot \frac{1}{2}\text{H}_2\text{O} + 1\frac{1}{2}\text{H}_2\text{O} \end{aligned}$

A unique property of POP is that when it is mixed with water, it reverts back to the hard solid form of gypsum. Because of this setting property, doctors use it to support fractured bones, and it is also used to make toys and decorative items.

Summary Table of Important Salts