The solution of hydrogen chloride in water is a chemical change. The physical change is that hydrogen chloride forms liquid hydrogen chloride under high pressure. This is hydrogen chloride dissolved in water, because hydrogen chloride can be miscible with water at 1:700, dissolved in water to form an ionic state, there is no molecular state.

A lot of people think it's a chemical change, but it's not strictly a physical change. Strictly speaking, hydrogen chloride dissolves in water to form a solution of hydrochloric acid.

How do you measure the amount of hydrogen chloride in the air? For this research, the amount of hydrogen chloride gas contained in the air is not much, and it is mixed with some other gases, so it brings some difficulties for the determination, so it is necessary to seek an effective method to complete.

Determination of hydrogen chloride

Studies have found that chloride ions can react with mercury thiocyanate to replace thiocyanate, so that ferric ions and sulfate will turn into blood red. The content can be judged and calculated according to the depth of the color. The chemical equation involved is as follows:

①2Cl-+Hg (SCN) 2→HgCl2+2SCN-

②SCN-+Fe3+→Fe (SCN) 2+