Here we're told that Zinc Sulfide reacts with aqueous hydrochloric acid to form Zinc Chloride and Hydrogen Sulfide gas. We are given the balanced chemical equation and asked what the mass of Hydrogen Sulfide formed is when 12.11 grams of Zinc Sulfide reacts with 15.92 grams of Hydrochloric Acid.
Step 1: We're going to convert the given quantities into moles. If any compound is in excess, then we just ignore it. We have 12.11 grams of zinc sulfide and 15.92 grams of hydrochloric acid. We calculate that 1 mole of Zinc Sulfide has a combined mass of 97.46 grams. This comes from adding the mass of Zinc (65.39 grams) and Sulfur (32.07 grams). We also find that 1 mole of HCl has a combined mass of 36.458 grams, considering that Hydrogen weighs 1.008 grams and Chlorine weighs 35.45 grams.
Next, we're going to do a mole-to-mole comparison to convert moles of each reactant into moles of the unknown, which is the mass of hydrogen sulfide. For every 1 mole of H2S, there is 1 mole of Zinc Sulfide and 2 moles of HCl according to the balanced equation.
Finally, we convert the moles of unknown into the final desired units, which is the mass of hydrogen sulfide. One mole of H2S (with 2 hydrogens and 1 sulfur) has a combined mass of 34.086 grams. When this is computed, we get two results: 4.235 grams of H2S and 7.442 grams of H2S. We compare these amounts to determine the theoretical yield. The smaller amount, 4.235 grams, is for the limiting reagent, indicating that Zinc Sulfide is our limiting reagent and HCl is our excess reagent.
The final answer is 4.235 grams of Hydrogen Sulfide. This smaller amount represents our theoretical yield, indicating that Zinc Sulfide is the limiting reactant while Hydrochloric Acid acts as the excess reactant.