Multiple Choice
How many grams of calcium hydride (CaH2) are required to produce 4.56 L of hydrogen gas (H2) at 25.0 °C and 0.975 atm according to the reaction: CaH2(s) + 2H2O(l) → Ca(OH)2(aq) + 2H2(g)?
3. Chemical Reactions
Stoichiometry
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How many grams of zinc metal are required to produce 3.5 liters of hydrogen gas at STP according to the chemical equation Zn(s) + 2 HCl(aq) → ZnCl2(aq) + H2(g)?
A
7.8 grams
B
9.5 grams
C
10.2 grams
D
12.0 grams
Verified step by step guidance1
Identify the balanced chemical equation: Zn(s) + 2 HCl(aq) → ZnCl2(aq) + H2(g). This tells us that 1 mole of Zn produces 1 mole of H2 gas.
Recall that at STP (Standard Temperature and Pressure), 1 mole of any gas occupies 22.4 liters. Therefore, calculate the moles of H2 gas produced using the volume given: \( \text{moles of } H_2 = \frac{3.5 \text{ L}}{22.4 \text{ L/mol}} \).
Using the stoichiometry of the reaction, determine the moles of Zn required. Since the reaction shows a 1:1 mole ratio between Zn and H2, the moles of Zn needed are equal to the moles of H2 calculated.
Calculate the mass of Zn required using its molar mass. The molar mass of Zn is approximately 65.38 g/mol. Use the formula: \( \text{mass of Zn} = \text{moles of Zn} \times 65.38 \text{ g/mol} \).
Compare the calculated mass of Zn with the given options to determine the correct answer.
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