There is a special gland in the stomach wall of humans and other animals that can turn the salt that they eat 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 needed to activate pepsin. It can also denature the protein in salt and be easily hydrolyzed, and kill the food. The effect of bacteria entering the stomach. In addition, after hydrochloric acid enters the small intestine, it can promote the secretion of pancreatic juice and intestinal juice, and the secretion and discharge of bile. The acidic environment also helps the absorption of iron and calcium in the small intestine.
Daily use
Utilize the property of hydrochloric acid to react with insoluble alkalis to prepare daily necessities such as toilet cleaner and rust remover.
Industrial applications
Hydrochloric acid is a strong inorganic acid, which is widely used in industrial processing, such as metal refining. Hydrochloric acid can often determine the quality of the product.
analytical chemistry
In analytical chemistry, when acid is used to determine the concentration of alkali, hydrochloric acid is generally used for titration. Titration with strong acid can make the end point more obvious, and the result obtained is more accurate. At 1 standard atmospheric pressure, 20.2% hydrochloric acid can form an azeotropic solution, which is often used as a reference material in quantitative analysis under a certain pressure. Its concentration at constant boiling will change with the change of air pressure. [28]
Hydrochloric acid is often used to dissolve solid samples for further analysis, including dissolving some metals and calcium carbonate or copper oxide to form easily soluble substances to facilitate analysis. [23] [24]
Pickled steel
One of the most important uses of hydrochloric acid is to pickle steel. Before subsequent processing of iron or steel (extrusion, rolling, galvanizing, etc.), hydrochloric acid can be used to react the rust or iron oxide on the surface. Usually use 18% hydrochloric acid solution as pickling agent to clean carbon steel: