In the laboratory preparation of Chlorine, the gas is passed through a wash bottle of water to

In the laboratory preparation of chlorine gas, concentrated hydrochloric acid (HCl) is reacted with manganese(IV) oxide (MnO₂). The chlorine gas produced is contaminated with hydrogen chloride (HCl) vapour and water vapour.

The gas is first passed through a wash bottle containing water. The purpose of this step is to absorb the HCl gas. Hydrogen chloride is extremely soluble in water and dissolves readily, while chlorine is only slightly soluble. This allows the HCl impurity to be removed selectively.

After this, the gas is typically passed through concentrated sulphuric acid to remove the remaining water vapour (drying), and then collected.

The water wash does not dilute the chlorine (chlorine is a gas, not a solution being diluted), does not neutralize it (that would require a base, not water), and does not absorb the Cl₂ (chlorine has low solubility in water, and the goal is to collect it, not remove it).