When sodium chloride reacts with concentrated sulphuric acid, the gas evolved is hydrogen chloride gas.
This common laboratory reaction is often used for the preparation of hydrogen chloride. As stated in the reference provided, "When sodium chloride is heated with sulphuric acid, a highly volatile colourless hydrogen chloride gas is produced." The reaction typically occurs when solid sodium chloride (NaCl) is mixed with concentrated sulphuric acid (H₂SO₄) and gently heated.
Understanding the Reaction
The reaction between sodium chloride and concentrated sulphuric acid is an example of a displacement reaction, specifically a reaction involving a non-volatile acid (sulphuric acid) displacing a more volatile acid (hydrochloric acid, from which HCl gas is evolved) from its salt.
The balanced chemical equation for this reaction is:
NaCl(s) + H₂SO₄(conc) → NaHSO₄(s) + HCl(g)
Here's a breakdown:
- Sodium Chloride (NaCl): The salt reactant.
- Sulphuric Acid (H₂SO₄): The concentrated acid reactant. It acts as a strong acid and dehydrating agent.
- Sodium Bisulphate (NaHSO₄): A solid salt product.
- Hydrogen Chloride (HCl): The gaseous product that is evolved.
Properties of Hydrogen Chloride Gas
The hydrogen chloride gas produced has several distinct properties:
- Colourless: As noted in the reference, it is a colourless gas.
- Volatile: It easily turns into a gas, especially upon heating.
- Pungent smell: It has a sharp, irritating odour.
- Acidic: When dissolved in water, it forms hydrochloric acid, a strong acid.
- Forms dense white fumes: When it comes into contact with moist air, it forms tiny droplets of hydrochloric acid, which appear as white fumes.
This reaction is a standard method for producing HCl gas in small quantities in a laboratory setting. Handling concentrated sulphuric acid and hydrogen chloride gas requires appropriate safety precautions due to their corrosive nature.
