What is the use of hydrochloric acid

The uses of hydrochloric acid are actually quite extensive, both for human use and in industrial use. Hydrochloric acid is a component of gastric juice that can denature the protein in food and facilitate hydrolysis, killing bacteria in the food that enters the stomach. It also helps the absorption of iron and calcium in the small intestine. It is used as an organic synthetic material in industry, and is also used in some bleaching and dyeing industries.

1. Human Use

Humans and other animals have a special gland in their stomach walls that converts ingested salt into hydrochloric acid. Hydrochloric acid is a component of gastric juice (concentration is about 0.5%). It can keep the gastric juice at the most suitable pH value required to activate pepsin. It can also denature the protein in food and facilitate hydrolysis, as well as kill bacteria that enter the stomach with food. In addition, after hydrochloric acid enters the small intestine, it can promote the secretion of pancreatic juice, intestinal juice, and the secretion and excretion of bile. The acidic environment also helps the absorption of iron and calcium in the small intestine.

2. Organic Synthesis

For example, at a temperature of 180°C to 200°C and with a mercury salt (such as HgCl2) as a catalyst, hydrogen chloride and acetylene undergo an addition reaction to produce vinyl chloride, which is then polymerized to form polyvinyl chloride under the action of an initiator.

3. Bleaching and dyeing industry

For example, hydrochloric acid is used for pickling cotton cloth after bleaching and for neutralizing residual alkali after mercerizing cotton cloth. During the printing and dyeing process, some dyes are insoluble in water and need to be treated with hydrochloric acid to become soluble hydrochlorides before they can be used.

4. Metal processing

For example, before plating, steel parts are first washed with an alkaline solution to remove oil stains and then soaked in hydrochloric acid. Before metal welding, a little hydrochloric acid needs to be applied to the weld, etc., all of which use the property of hydrochloric acid to dissolve metal oxides to remove rust. In this way, the metal surface can be plated and welded firmly. It is also possible to remove materials by means of corrosion by dissolving some metals (such as aluminum).