The diagram shows hydrogen gas being generated from the reaction of zinc granules with dilute hydrochloric acid. This gas then passes through a U-tube containing "Substance Z" before reacting with cop

The diagram shows hydrogen gas being generated from the reaction of zinc granules with dilute hydrochloric acid. This gas then passes through a U-tube containing "Substance Z" before reacting with copper(II) oxide. The purpose of the U-tube containing Substance Z in this setup is to remove moisture from the hydrogen gas, as hydrogen produced from an aqueous solution will be wet.

Common drying agents suitable for hydrogen gas include concentrated sulfuric acid, anhydrous calcium chloride, and silica gel. Since Substance Z is placed in a U-tube, a solid drying agent is typically used.

Anhydrous calcium chloride is a commonly used solid drying agent for gases like hydrogen, often packed in U-tubes.

Substance Z: Anhydrous calcium chloride