Hydrogen Chloride — Part 1: Preparation and physical properties: visual lesson, ICSE Class 10 Chemistry (Science Paper 2)

Lesson

A gas that fumes in moist air

Part 1 — Hydrogen chloride is a colourless gas with a sharp, choking smell. Open a jar of it in damp air and it forms misty white fumes: tiny droplets of hydrochloric acid.

In this lesson you will

Write the equation and describe the apparatus for preparing hydrogen chloride in the laboratory
Explain the choice of drying agent and method of collection
Describe experiments that show hydrogen chloride is heavier than air and very soluble in water
Explain how the inverted funnel prevents back suction when making hydrochloric acid

Table of the physical properties of hydrogen chloride
Property	Hydrogen chloride
Colour and smell	Colourless; pungent, choking
Density	Heavier than air (vapour density 18.25)
Solubility in water	Extremely soluble
In moist air	Fumes
Effect on moist litmus	Blue turns red

Concept

The reaction

Sodium chloride (rock salt) is heated gently with concentrated sulphuric acid, keeping the temperature below 200 °C. The acid gives its hydrogen to the chloride, forming sodium hydrogensulphate and hydrogen chloride.

Above 200 °C the reaction goes further to sodium sulphate, which is avoided (see the worked example).

\ce{NaCl + H2SO4 -> NaHSO4 + HCl}

Laboratory preparation, below 200 °C

Diagram

The apparatus

Flask: sodium chloride + concentrated sulphuric acid added through a thistle funnel; gentle heat.
Wash bottle: concentrated sulphuric acid dries the gas.
Gas jar: kept upright; the gas enters at the bottom and pushes the air out — upward displacement of air.

Cookies