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CSEC Chemistry: Salts

(This is a continuation of previous posts on acids and bases)

A salt is a substance formed when metal ions or the ammonium ion take the place of the hydrogen ion(s) of an acid.

NaOH(aq) + HNO₃(aq) → NaNO₃(aq) + H₂O(l)

Here, the sodium ion from sodium hydroxide takes the place of the hydrogen ion in nitric acid. The salt formed is sodium nitrate.

However, these salts can be either normal salts or acid salts. Salts formed by monobasic acids will always be normal salts, since all the hydrogen ions will be replaced. However, in dibasic and tribasic acids, the hydrogen ions of the acid may be either partially or completely replaced, forming:

  1. a normal salt if all of the hydrogen ions are replaced. Normal salts are completely neutral.

  2. an acid salt if the hydrogen ions are partially replaced. Acid salts are acidic.

For example, the dibasic sulfuric acid (H₂SO₄) produces two different salts:

NaOH(aq) + H₂SO₄(aq) → NaHSO₄(aq) + H₂O(l)

acid salt

2NaOH(aq) + H₂SO₄(aq) → NaSO₄(aq) + 2H₂O(l)

normal salt

Salts in Everyday Life

Calcium carbonate is used in the manufacture of cement and decorative stones.

sodium chloride, sodium nitrite, sodium nitrate, and sodium benzoate are used in food preservation.

Calcium sulfate is used in Plaster of Paris for making casts and is also found in gypsum, which is used in plastering walls.

Magnesium sulfate heptahydrate is Epsom salts which is a laxative. Magnesium sulfate decahydrate is Glauber salt which is also a laxative.

Sodium nitrate however, is implicated in causing brain damage in infants and also suspected to be carcinogenic.

Copper (II) Sulphate is used as a fungicide.

Ammonium sulphate is used as fertilizer (it replenishes the soil with nitrogen ions).

Iron (II) sulphate, mercury chloride, sodium arsenate and sodium chlorate (V) are used as pesticides to kill insects, pests weed and fungi.

Potassium manganate (VII) is used as a disinfectant.

Sodium hydrogencarbonate is an ingredient in antacids to neutralize the excess hydrochloric acid secreted by the stomach.

(You can find some more applications here)

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