Chemists frequently prepare hydrogen gas in the laboratory by the reaction of zinc and hydrochloric acid. Th e other product is ZnCl₂(aq). Calculate the volume of hydrogen produced at 744 torr pressure and 27 °C by the reaction of 32.2 g zinc and 500 mL of 2.20 M HCl .

Strategy

The strategy of this example is interesting, because we use three different methods to calculate the number of moles of the three different substances:

(1) Use the molar mass to calculate the number of moles from the mass of zinc.

(2) Use the molarity and the volume of solution to calculate the number of moles of HCl.

(3) Use the ideal gas law to convert the number of moles of hydrogen gas to volume of hydrogen gas. As always, use the chemical equation to relate the number of moles of one substance to moles of another.