A colourless gas that fumes in moist air and is so soluble in water that a whole flask can empty itself in a fountain.
Hydrogen chloride is made by gently heating sodium chloride with concentrated sulphuric acid: NaCl + H₂SO₄ → NaHSO₄ + HCl. At a higher temperature the sodium hydrogen sulphate reacts further: NaHSO₄ + NaCl → Na₂SO₄ + HCl. The gas is dried with concentrated sulphuric acid and collected by upward displacement of air.
Why is hydrogen chloride collected by upward displacement of air and not over water?
It is heavier than air (vapour density 18.25 against 14.5 for air) and extremely soluble in water
Why is concentrated sulphuric acid used to dry the gas?
It absorbs water but does not react with hydrogen chloride
How is hydrochloric acid made from the gas in the laboratory?
The gas is dissolved in water through an inverted funnel that just touches the surface, which stops water being sucked back
Hydrogen chloride is a colourless gas with a pungent smell that fumes in moist air. The fountain experiment shows its very high solubility. Dissolved in water it gives hydrochloric acid, a strong acid that reacts with reactive metals: Zn + 2HCl → ZnCl₂ + H₂. Warm concentrated acid and manganese dioxide give chlorine: MnO₂ + 4HCl → MnCl₂ + 2H₂O + Cl₂.
How is hydrogen chloride tested using ammonia?
A glass rod dipped in ammonia solution gives dense white fumes of ammonium chloride in the gas: NH₃ + HCl → NH₄Cl
What is seen when silver nitrate solution is added to hydrochloric acid?
A white curdy precipitate of silver chloride, soluble in ammonium hydroxide: AgNO₃ + HCl → AgCl + HNO₃
What is aqua regia?
A mixture of 3 parts concentrated hydrochloric acid and 1 part concentrated nitric acid by volume; it dissolves gold and platinum
1. Write the equation for the laboratory preparation of hydrogen chloride, below 200 °C.
2. Name the drying agent used for hydrogen chloride gas.
3. Why is hydrogen chloride not collected over water?
4. What is the vapour density of hydrogen chloride? (H = 1, Cl = 35.5)
5. What does the fountain experiment show about hydrogen chloride?
6. How is hydrogen chloride gas tested using ammonia?
7. What precipitate forms when silver nitrate is added to hydrochloric acid?
8. What is aqua regia, and what does it dissolve?
9. Write the equation for zinc reacting with dilute hydrochloric acid.
10. Why is an inverted funnel used when dissolving hydrogen chloride in water?