HCl
Hydrochloric acid (HCl)
Also known as: muriatic acid, hydrogen chloride (gas)
HCl is hydrogen chloride — a sharp, colourless gas that becomes hydrochloric acid when dissolved in water. It is the textbook strong acid, ionising completely into H⁺ and Cl⁻, and it is also entirely natural: your stomach secretes it at around 0.1 M to digest food and kill microbes.
Molar mass breakdown
36.458 g/mol| Element | Atoms | Mass (g/mol) | % by mass |
|---|---|---|---|
| Chlorine (Cl) | 1 | 35.45 | 97.24% |
| Hydrogen (H) | 1 | 1.008 | 2.765% |
What hydrochloric acid is used for
- Stomach acid — digestion and defence
- Steel pickling (removing rust before coating)
- pH control in industry and pools
- Laboratory standard strong acid
Key facts
- Molar mass ≈ 36.46 g/mol.
- Fully ionises: a 0.01 M solution has pH 2 exactly.
- Classic acid-metal reaction: 2HCl + Zn → ZnCl₂ + H₂↑.
Frequently asked questions
What is the molar mass of HCl?
About 36.46 g/mol: 1.008 (H) + 35.45 (Cl).
What is the pH of 0.1 M HCl?
pH 1. As a strong acid it ionises fully, so [H⁺] = 0.1 M and pH = −log(0.1) = 1.
Is stomach acid really hydrochloric acid?
Yes — parietal cells secrete HCl at roughly pH 1.5–2. A mucus layer protects the stomach wall from digesting itself.