Acids, Bases and Salts

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• Questions
• Summary

Salts are the ionic compounds which are produced after the neutralization reaction between acid and base. Salts are electrically neutral.

Characteristics of salt

1. Most of the salts are crystalline solid
2. Salts may be transparent or opaque
3. Most of the salts are soluble in water
4. Solution of salts conducts electricity. Salts conduct electricity in their molten state also
5. The salt may be salty, sour, sweet, bitter and umami (savoury)
6. Neutral salts are odourless
7. Salts can be colourless or coloured

Sodium Hydroxide (NaOH): When electricity is passed through an aqueous solution of NaCl (brine), it decomposes to form NaOH.

(Chlor-alkali process)

2NaCl + 2H₂O → 2NaOH + Cl₂ + H₂
At anode: Cl₂ gas
At cathode: H₂ gas
Near cathode: NaOH solution is formed.

Uses :

1. H₂: Fuels, margarine
2. Cl₂: Water treatment, PVC, CFC’s
3. HCl: Cleaning steels, medicines
4. NaOH: Degreasing metals, soaps and papermaking
5. Cl₂ + NaOH → Bleach: Household bleaches, bleaching fabrics

Bleaching Powder (CaOCl₂): It is produced by the action of chlorine on dry slaked lime.

Cl₂ + Ca(OH)₂ → CaOCl₂ + H₂O

Uses :

1. Bleaching cotton and linen in textile industry.
2. Bleaching wood pulp in paper factories.
3. Oxidizing agent in chemical industries.
4. Disinfecting drinking water.

Baking Soda (Sodium Hydrogen Carbonate) (NaHCO₃) :

NaCl + H₂O + CO₂ + NH₃→ NH₄Cl + NaHCO₃

Uses:

1. Baking soda is used in making of baking powder, which is used in cooking as it produces carbon dioxide which makes the batter soft and spongy.
2. Baking soda is used as an antacid.
3. Baking soda is used in toothpaste which makes the teeth white and plaque free.
4. Baking soda is used in cleansing of ornaments made of silver.
5. Since sodium hydrogen carbonate gives carbon dioxide and sodium oxide on strong heating, thus it is used as fire extinguisher.

Washing Soda (Na2CO3.10H2O): Recrystallization of sodium carbonate gives washing soda. It is a basic salt.

Na₂CO₃ + 10H₂O → Na₂CO₃.10H₂O

Uses :

1. In glass, soap and paper industry.
2. Manufacture of borax.
3. Cleaning agent for domestic purposes.
4. For removing permanent hardness of water.

Classification of salts

Normal salts
A normal salt is obtained by complete neutralization of an acid by a base
NaOH + HCl → NaCl + H₂O

Acid Salts
Acid salts are derived by the partial replacement of hydrogen ions of an acid by a metal. When a calculated amount of a base is added to a polybasic acid, acid salt is obtained, as follows.

NaOH + H₂SO₄ → NaHSO₄ + H₂O

Basic Salts
Basic salts are formed by the partial replacement of hydroxide ions of a diacidic or triacidic base by an acid radical. A basic salt may further react with an acid to give a normal salt.

Pb(OH)2 + HCl → Pb(OH)Cl + H2O
Diacidic base Basic salt

Double salts
Double salts are formed by the combination of a saturated solution of two simple salts in equimolar ratio followed by crystallization. e.g. potash alum

Salt of the family

Salts having common acidic or basic radicals are said to belong to the same family.

Example

1. Sodium chloride (NaCl) and Calcium chloride (CaCl2) belong to chloride family.
2. Calcium chloride (CaCl2) and calcium sulphate (CaSO4) belong to calcium family.
3. Zinc chloride (ZnCl2) and Zinc sulphate (ZnSO4) belong to zinc family.

Salts produced because of reaction between strong acid and strong base are neutral in nature. The pH of value of such salts is equal to 7, i.e. neutral. Example; Sodium chloride, sodium sulphate, potassium chloride, etc

1. When a strong acid reacts with a weak base, the base is unable to fully neutralize the acid. Due to this, an acidic salt is formed in this case.
2. When a strong base reacts with a weak acid, the acid is unable to fully neutralize the base. Due to this, a basic salt is formed in this case.
3. When equally strong acid and base react they fully neutralize each other. Due to this, a neutral salt is formed in this case.