Properties of Acids

• Acid is a compound that forms hydrogen ions (H⁺) when dissolved in water.
  HCl + H₂O → H⁺ + Cl⁻
• Acid is sour to taste and corrosive in nature. The pH of acids is less than 7.
• All acids react with the metal to release hydrogen gas. For example, zinc metal reacts with hydrochloric acid to form zinc chloride and hydrogen gas.
  Zn + 2HCl → ZnCl₂ + H₂
• When acids react with limestone (CaCO₃), it produces carbon dioxide. For example, HCl reacts with limestone to produce carbonic acid and calcium chloride.
  CaCO₃ + 2HCl → CaCl₂ + CO₂ + H₂O
• Acids are classified into organic and inorganic acids. The best example of an organic acid is acetic acid (CH₃COOH), and inorganic acids are produced from minerals; for example, sulphuric acid (H₂SO₄) and hydrochloric acid. 
• Acid usually converts blue litmus paper to red litmus paper.

1. Acids tend to corrode metal surfaces quickly.
2. Some acids are highly corrosive.
3. In an acidic solution, methyl orange gives a red colour.
4. Acids turn the pink colour of phenolphthalein to colourless.

Examples of acids: lemons, oranges, vinegar, sulphuric acid, and hydrochloric acid.

Uses of Acids: Benzoic acid (salt used to preserve food),

Carbonic Acid: Used to make carbonated drinks. 

Ethanoic acid: Used to clean metals before electroplating/processing leather/household cleaning/maintenance of swimming pools.

Sulphuric acid: To make fertilizers, polymers, and detergent

Strong acids: These acids get completely (100%) ionised in the aqueous solutions. Thus, at equilibrium, the concentration of acid molecules becomes significantly less, and the concentration of hydrogen ions reaches the maximum; for example, HCl, HNO₃, and HClO₄.

Weak acids: These acids are only partially ionised in solution at an equilibrium state. At the equilibrium state, molecules of acid are present in a considerable amount, and the concentration of hydrogen ions is less, for example, HF, CH₃COOH.