Dilute hydrochloric acid, that is, hydrochloric acid with mass fraction less than 20%, the chemical formula of solute is HCl. Dilute hydrochloric acid is a colorless and clear liquid with strong acidity. It has pungent smell and belongs to pharmaceutical excipients and pH regulator.
Dilute hydrochloric acid can be used to remove the scale in boiling water (chemical equation): CaCO3+2HCl=CaCl2+H2O+CO2↑ and Mg(OH)2+2HCl=MgCl2+2H2O). The carbon dioxide produced in the laboratory is (chemical equation): CaCO3+2HCl=CaCl2+H2O+CO2↑, which reacts with metals such as iron and magnesium to generate a small amount of hydrogen (required for chemical experiments).