Salts and their uses

A salt forms when an acid and a base neutralise each other. Salts with the same positive part or the same negative part form a family: NaCl and Na₂SO₄ are both sodium salts; NaCl and KCl are both chlorides.

Is a salt acidic, basic or neutral? Find its parents. Write the acid and the base it came from, and mark each strong or weak:

The stronger parent decides.

Common salt (NaCl) is the starting point for many chemicals. Pass electricity through brine (salt water) and you get three useful products. This is the chlor-alkali process:

2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂

Chlorine forms at the anode, hydrogen at the cathode, and sodium hydroxide near the cathode.

For each chemical, remember four things: name, formula, how it is made, uses.

Why do dhokla and cakes rise? On heating, baking soda gives off carbon dioxide:

2NaHCO₃ → Na₂CO₃ + H₂O + CO₂

The gas bubbles make the batter soft and spongy. Baking powder adds a mild acid (tartaric acid) to stop the food tasting bitter.

Water of crystallisation is a fixed number of water molecules inside each crystal. Blue copper sulphate, CuSO₄·5H₂O, turns white when heated as it loses this water. Add a few drops of water and it turns blue again.

Plaster of Paris is gypsum that has lost most of its water. Mix the white powder with water and it sets hard into gypsum again, like the plaster cast on a broken arm that your friends sign. That is also why it must be kept in a moisture-proof container.