More practice questions

4. Q4. Which contains more molecules: 1.0 g of hydrogen gas (H₂, 2.016 g mol^⁻¹) or 10.0 g of oxygen gas (O₂, 32.00 g mol^⁻¹)?

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   H₂: 1.0/2.016 ≈ 0.50 mol. O₂: 10.0/32.00 ≈ 0.313 mol. The hydrogen has more molecules, even though its mass is ten times smaller.

5. Q5. What volume does 8.0 g of oxygen gas (O₂) occupy at 273.15 K and 1 bar? Take the molar volume as 22.7 L mol^⁻¹.

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   n = 8.0/32.00 = 0.25 mol. V = 0.25 × 22.7 ≈ 5.7 L.

6. Q6. How many electrons are there in 1.8 g of water (M = 18.02 g mol^⁻¹)? Each H₂O molecule has 10 electrons.

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   n ≈ 1.8/18.02 ≈ 0.10 mol of molecules, so 0.10 × 10 = 1.0 mol of electrons, that is, about 6.0 × 10^²³ electrons.

7. Q7. Show from NCERT’s data that one mole of carbon-12 atoms contains about 6.022 × 10^²³ atoms: one atom has mass 1.992648 × 10^⁻²³ g, and one mole has mass 12 g.

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   N = 12 g/(1.992648 × 10^⁻²³ g) ≈ 6.0221 × 10^²³ atoms.