Question

When the chemicals iron sulfide (FeS) and hydrochloric acid (HCl) are combined, bubbles appear from the mixture. 1. Does the appearance of bubbles indicate a physical or chemical change? 2. Why do the bubbles indicate this change? 3. What property is this?

Answer 1

The reaction of iron sulfide (FeS) with hydrochloric acid (HCl) results in the formation of ferrous chloride (FeCl2) and hydrogen sulfide (H2S) gas. The reaction can be shown as follows:

FeS (s) + HCl(aq) ---- FeCl2(s) + H2S(g)

The bubbles indicate the formation of H2S gas which is a chemical change. The formation of bubbles indicates this change as it suggests that the reactants are combing to form products i.e. it signals a chemical reaction.