Hydrochloric acid is the aqueous solution of hydrogen chloride (HCl) and serves numerous industrial purposes. It is a transparent liquid ranging from colourless to pale yellow, with a sharp, irritating smell and strong corrosive traits. The 38% hydrochloric acid solution has a melting point of -27.32°C and its boiling point sits at roughly 48°C.
Concentrated hydrochloric acid generally contains about 37% hydrogen chloride by weight and possesses high volatility. Once the container of concentrated hydrochloric acid is unsealed, hydrogen chloride gas will easily escape into the ambient air.
| Foreign Name | Hydrochloric acid |
| Chemical Formula | HCI (aq) |
| Molecular Weight | 36.46 |
| CAS Number | 7647-01-0 |
| Melting Point | -27.32 ℃ (38% solution) |
| Boiling Point | 48 ℃ (38% solution) |
| Water Solubility | Frequently soluble in water |
| Appearance | Colorless to pale yellow clear liquid |
| Flash point | Non-flammable |
| Applications | Extracts refined salts, etc. |
| Acidity coefficient | -8 |
| Viscosity | 1.9 mPas (25℃, 31.5% solution) |
Hydrochloric acid boasts many critical functions within the chemical sector and contributes greatly to stable product quality control. It is widely adopted for steel descaling, and acts as an indispensable chemical reagent for mass manufacturing of numerous inorganic and organic substances, among which vinyl chloride — the primary precursor for PVC plastics — stands out.
This acid also covers many small‑scale usage scenarios, such as domestic cleaning, the production of gelatin and other food additives, scale‑removing preparations, and leather treatment. Moreover, hydrochloric acid constitutes the main component of gastric juice, assisting digestion and defending the body against microbial invasion.
