How many moles of H₂ can be formed if a 2.97 g sample of Mg reacts with excess HCl according to the reaction: Mg + 2HCl → MgCl₂ + H₂?

• A. 0.244 moles
• B. 0.122 moles
• C. 0.183 moles
• D. 0.061 moles

Answer: (B)

Verified step by step guidance

1. Determine the molar mass of magnesium (Mg) by using the periodic table. The atomic mass of Mg is approximately 24.31 g/mol.
2. Calculate the number of moles of Mg in the 2.97 g sample using the formula: \( \text{moles of Mg} = \frac{\text{mass of Mg}}{\text{molar mass of Mg}} \).
3. Write the balanced chemical equation for the reaction: \( \text{Mg} + 2\text{HCl} \rightarrow \text{MgCl}_2 + \text{H}_2 \).
4. Use the stoichiometry of the balanced equation to find the moles of \( \text{H}_2 \) produced. According to the equation, 1 mole of Mg produces 1 mole of \( \text{H}_2 \).
5. Calculate the moles of \( \text{H}_2 \) formed using the moles of Mg calculated in step 2, since the ratio is 1:1.