Hydrochloric acid

Hydrochloric acid is an aqueous solution of hydrogen chloride (HCl). It is a colorless strong acid and a component of the gastric acid of multiple species including humans.

Uses

As with many other acids hydrochloric acid is used to catalyze certain organic reactions. HCl is also used for pH neutralization of bases and the Pickling of steel. Furthermore it has a wide range of processing and cleaning applications.

Pickling of steel

Hydrochloric acid can be used in the pickling of steel to remove rust. A typical rust removal using HCl goes as follows:

Fe₃O₄ + Fe + 8HCl → 4FeCl₂ + 4H₂O

This reaction reacts with the iron oxide present on the steel until it is depleted as long as HCl is added in excess.

The FeCl2 byproduct can be recycled by hydrochloric acid regeneration process to recover some of the spent HCl.

Hydrogen Gas Production

Hydrochloric acid can produce Hydrogen gas when reacted with metals more reactive than hydrogen. In this reaction the metal reduces the Hydrogen ions in the Hydrochloric Acid. The product of this reaction is Hydrogen gas and a metal chloride salt.

Examples of this reaction

Zinc:

Zn_(s) + 2HCl_(aq) → ZnCl_{2(aq) +} H_2(g)

Magnesium:

Mg_(s) + 2HCl_(aq) → MgCl_{2(aq) +} H_2(g)

Iron:

Fe_(s) + 2HCl_(aq) → FeCl_{2(aq) +} H_2(g)

Safety

Hydrochloric acid releases toxic vapors when in an open container. Hydrochloric acid also causes skin burns, damage to eyes and is corrosive to metals. Concentrated hydrochloric acid is volatile at room temperature.

When handeling hydrochloric acid the following are essential for safety:

• Acid resistant gloves
• Safety glasses
• Labcoat (polyester material recommended)
• Acid neutralizer
• A well ventilated area
• Hazardous waste disposal containers
• An emergency shower and eye washing tap

Avoid inhalation of fumes and avoid contact. In case of contact wash with water.