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Study of Compounds – Hydrogen Chloride

ICSE Grade 10 Chemistry - Chapter 8

📚 Smart Summary

1. Preparation of HCl

Laboratory Preparation: NaCl + H₂SO₄ → NaHSO₄ + HCl↑ (below 200°C). Heating common salt with conc. H₂SO₄.

Setup: Round bottom flask with delivery tube. NaCl is heated with conc. H₂SO₄. HCl gas collected by upward displacement of air (denser than air).

Drying: Passed through conc. H₂SO₄ (hygroscopic drying agent). Cannot use CaCl₂ (reacts with HCl).

Why H₂SO₄: Non-volatile, less volatile than HCl, displaces HCl from chlorides.

Industrial Preparation: Direct combination - H₂ + Cl₂ → 2HCl (in presence of sunlight).

Laboratory setup for HCl gas preparation

Laboratory preparation of hydrogen chloride gas using sodium chloride and concentrated sulfuric acid

2. Properties of HCl

Physical: Colorless, pungent-smelling gas. Heavier than air (M = 36.5). Highly soluble in water (1:500 ratio).

Fountain Experiment: Demonstrates high solubility. Water rushes into flask containing HCl creating fountain effect.

Acidic Nature: Dissolves in water to form hydrochloric acid. HCl → H⁺ + Cl⁻. Turns blue litmus red.

Chemical Properties: Reacts with NH₃ to form white fumes of NH₄Cl. HCl + NH₃ → NH₄Cl↓ (white fumes - test for HCl).

With Metals: Zn + 2HCl → ZnCl₂ + H₂↑. With Carbonates: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂↑

Aqua Regia: HCl : HNO₃ in 3:1 ratio. Can dissolve noble metals like gold and platinum.

3. Tests and Uses

Test for HCl Gas: White fumes with NH₃. Glass rod dipped in NH₄OH held near HCl gives dense white fumes.

Test for Cl⁻ ions: AgNO₃ gives white precipitate of AgCl, soluble in NH₄OH. NaCl + AgNO₃ → AgCl↓ (white) + NaNO₃.

Uses: Manufacturing of aqua regia, cleaning metals (pickling), making chlorides, refining sugar, medicines.

Hydrochloric Acid: Aqueous solution of HCl. Strong mineral acid. Gastric juice contains dilute HCl (aids digestion).

🎯 Test Your Knowledge

Multiple Choice Questions

1. HCl is prepared in lab by heating NaCl with:

2. HCl gas is dried using:

3. HCl gas is collected by:

4. The test for HCl gas is:

5. Aqua regia is a mixture of:

6. Assertion (A): HCl cannot be dried using CaCl₂. Reason (R): CaCl₂ reacts with HCl.

7. The molecular mass of HCl is:

8. HCl is highly soluble in water because:

9. The fountain experiment demonstrates:

10. In industrial preparation, HCl is prepared by:

11. HCl gas turns moist blue litmus:

12. When HCl reacts with zinc, the gas evolved is:

13. The white precipitate formed when AgNO₃ reacts with HCl is:

14. Gastric juice in stomach contains:

15. HCl is collected by upward displacement of air because it is:

16. Which of the following is the correct laboratory preparation of HCl gas?

17. Assertion (A): HCl gas is collected by upward displacement of air. Reason (R): HCl is lighter than air.

18. Which salt is formed when HCl reacts with ammonia?

19. What happens when HCl gas is passed through blue litmus paper?

Practice Numericals

Practice Problem 1: Calculate the volume of HCl gas produced when 5.85 g of NaCl reacts with excess H₂SO₄. (Atomic masses: Na=23, Cl=35.5)