 In the double displacement reaction of a metal sulfide with an acid, we'll start out with a small amount of sodium sulfide. We'll add an aqueous solution of hydrochloric acid. The sodium sulfide and hydrochloric acid react to produce hydrogen sulfide. The hydrogen sulfide is released as a gas. We can test for the presence of hydrogen sulfide by bringing in a strip of wet lead acetate paper. The hydrogen sulfide reacts with the lead acetate paper to form lead sulfide, which is a brown-black precipitate.