Stoichiometry of hydrogen evolution:\nHow many grams of zinc (atomic weight 65) are needed to produce 224 cm³ of H₂ at NTP when reacted with dilute H₂SO₄ (Zn + H₂SO₄ → ZnSO₄ + H₂)?

Introduction / Context:
Gas evolution problems at Normal Temperature and Pressure (NTP) are classic stoichiometry exercises. Using molar volume and balanced equations, we convert a measured gas volume into moles and then into required reactant mass. This is common in lab-scale hydrogen generation and material balance checks.

Given Data / Assumptions:

• Balanced reaction: Zn + H2SO4 → ZnSO4 + H2.
• Volume of H2 at NTP = 224 cm³ = 0.224 L.
• Molar volume at NTP ≈ 22.4 L/mol.
• Atomic weight of Zn = 65 g/mol.

Concept / Approach:
The reaction stoichiometry is 1:1 between Zn and H2 (one mole of zinc yields one mole of hydrogen gas). Therefore, moles of zinc required equal moles of hydrogen desired. Convert the given volume of H2 to moles using the molar volume at NTP, then multiply by zinc’s molar mass to find the mass of zinc required.

Step-by-Step Solution:

Verification / Alternative check:
Cross-check using 22400 cm³ per mole: 224 cm³ / 22400 cm³/mol = 0.0100 mol → same result.

Why Other Options Are Wrong:

• 0.065 g: corresponds to 0.001 mol Zn (ten times too small).
• 6.5 g and 65 g: correspond to 0.1 and 1.0 mol, far too large.
• 1.30 g: double the required amount.

Common Pitfalls:
Using STP/NTP molar volume inconsistently or forgetting the 1:1 molar relationship in the balanced equation.

Final Answer:
0.65 g.