What is the purpose of the graduated cylinder in the collection of hydrogen gas by water displacement? What other type of laboratory glassware can fulfill this role? 2. 3. A 0.286-g sample of Zn was used to produce H2(g) by the reaction Zn(s) + 2HCI(aq)-â ZnCl2(aq) + H2(g). The barometric pressure was recorded as 761.6 mm Hg and room temperature was 20°C. When the water levels of the eudiometer tube and graduated cylinder were equal, the volume of H2 was measured as 94.8 mL. Calculate the number of moles of hydrogen gas produced in the reaction Also, calculate the theoretical number of moles that can be obtained with the given amount of metal. (Assume the acid is in excess.) Finally, determine a error.