When magnesium (Mg) reacts completely with excess hydrochloric acid (HCl), how many grams of hydrogen gas (H2) will be produced from 12 grams of Mg? (Reaction: Mg + 2HCl → MgCl2 + H2)

• A. 4.0 g
• B. 2.0 g
• C. 1.0 g
• D. 6.0 g

Answer: (B)

Verified step by step guidance

1. Write the balanced chemical equation for the reaction: \(\mathrm{Mg} + 2\mathrm{HCl} \rightarrow \mathrm{MgCl}_2 + \mathrm{H}_2\).
2. Calculate the number of moles of magnesium (Mg) used by dividing the given mass by the molar mass of Mg: \(\text{moles of Mg} = \frac{12\ \mathrm{g}}{24.305\ \mathrm{g/mol}}\).
3. Use the stoichiometry of the balanced equation to find the moles of hydrogen gas (\(\mathrm{H}_2\)) produced. According to the equation, 1 mole of Mg produces 1 mole of \(\mathrm{H}_2\), so moles of \(\mathrm{H}_2\) = moles of Mg.
4. Calculate the mass of hydrogen gas produced by multiplying the moles of \(\mathrm{H}_2\) by the molar mass of \(\mathrm{H}_2\) (2.016 g/mol): \(\text{mass of } \mathrm{H}_2 = \text{moles of } \mathrm{H}_2 \times 2.016\ \mathrm{g/mol}\).
5. The result from step 4 gives the mass of hydrogen gas produced from 12 grams of magnesium reacting completely with excess hydrochloric acid.