With respect to the laboratory preparation of HCl gas, answer the following questions :

(a) Name the reactants used and the product(s) formed.

(b) Under what conditions do the reactants react?

(c) How is the gas identified?

(d) State the precautions to be taken.

(a) Reactants: Sodium chloride (common salt) and concentrated sulphuric acid.

Products: Hydrogen chloride gas and Sodium bisulphate (at low temperatures) or Sodium sulphate (at high temperatures).

(b) Conditions of reaction:

The reaction typically occurs in two stages depending on the temperature:
Below 200°C: The reaction yields sodium bisulphate.

$\text{NaCl} + \text{H}$2\text{SO}4 \xrightarrow{\lt 200 \degree\text{C}} \text{NaHSO}_4 + \text{HCl} \uparrow

Above 200°C: If the temperature is increased further, the sodium bisulphate reacts with more salt to form sodium sulphate. However, this is usually avoided in labs to protect the glass apparatus and prevent the formation of a hard crust.

(c) Identification of the gas :
Bring a glass rod dipped in ammonia solution near the jar mouth; dense white fumes of ammonium chloride (NH₄Cl) forms.
It also turns moist blue litmus paper red, showing its acidic nature.

(d) Precautions to be taken :

1. The lower end of the thistle funnel must be dipped in conc. sulphuric acid.
2. Delivery tube should be dipped in drying agent i.e., conc. H₂SO₄.
3. Avoid temperatures above 200°C to prevent glass apparatus from cracking, wasting fuel, and forming a hard sodium sulphate crust.