Making hydrogen chloride, and the test that names it
Hydrogen chloride is made in the laboratory from the cheapest chloride there is: common salt, warmed with concentrated sulphuric acid. The acid is less volatile than hydrogen chloride, so it drives the gas out of the salt. This activity runs the preparation, leads the gas down a delivery tube into a jar, and then puts it through the two tests every Class 10 answer gives: it turns moist pH paper red, and a glass rod dipped in ammonia solution, held in it, raises dense white fumes.
8 steps · Hydrogen Chloride · Study of Compounds
What you will use
Apparatus
- Generating flask
- Gas jar
Chemicals
- Sodium Chloride
- Concentrated Sulfuric Acid
- Ammonia Solution
The steps
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Put rock salt (sodium chloride) into the generating flask.
White crystals. Salt on its own gives off nothing.
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Right-click the flask and run a delivery tube into the gas jar.
Set up first. Hydrogen chloride is heavier than air, so it collects in an upright jar by pushing the air out above it.
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Pour concentrated sulphuric acid onto the salt.
Some fizzing even cold, but the reaction needs warmth to keep going.
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Attach a burner under the flask.
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Warm the flask gently.
A steady stream of colourless gas comes off and passes down the tube.
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Look at the gas jar.
It fills with a colourless gas that fumes where it meets the moist air at the mouth of the jar.
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Hold a strip of moist pH paper in the gas jar.
It turns red. Dry hydrogen chloride is not an acid; it acts as one the moment it meets water.
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Dip the glass rod in ammonia solution and hold it in the gas jar.
Dense white fumes billow from the tip of the rod.
What it shows
Concentrated sulphuric acid drives hydrogen chloride out of sodium chloride, leaving sodium bisulphate behind. The temperature is kept below 200 °C on purpose: hotter, the reaction goes on to 2NaCl + H₂SO₄ → Na₂SO₄ + 2HCl, which costs more fuel and leaves a hard crust of sodium sulphate that can crack the flask. The white fumes at the rod are ammonium chloride, NH₃ + HCl → NH₄Cl, the test that names the gas.