Stoichiometry Problem

Question

Hydrogen gas is produced when Zinc reacts with hydrochloric acid. How many grams of zinc are needed to produce 112 L of H₂ at STP?

                                Zn + 2HCl → ZnCl₂ + H₂

Answer 1

Since this is a stoichiometry problem, and you have been given a chemical reaction, you must utilize the coefficients of the reaction in your calculation.

This problem specifically mentions Zn and H_2. There is 1 mole of Zn and 1 mole of H₂ in the balanced equation.

  Zn + 2HCl → ZnCl₂ + H₂

You are also given: 112 L of H₂ at STP

STP is a standard condition stating that for 1 mole of gas, 22.4 L will be occupied.

Now you can set up your stoichiometry problem:

112 L H_{2 *} (1 mol H₂ / 22.4 L) * (1 mol Zn / 1 mol H₂) = 5.0 mol Zn

convert moles to grams using molar mass of Zn

5.0 mol Zn * (65.38 g Zn / 1 mol Zn) = 326.9 grams or 327 grams (rounded)

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