Practice Questions

Atomic mass = mass of one atom × Avogadro's number = 2.66 × 10⁻²³ × 6.022 × 10²³ ≈ 16 u.

4.6 g Na = 0.2 mol. From the equation, 2 mol Na produce 1 mol H₂. Hence 0.2 mol Na produces 0.1 mol H₂.

One formula unit produces 5 ions (2 Al³⁺ + 3 SO₄²⁻). Therefore, 0.1 mol gives 0.5 mol ions = 3.011 × 10²³ ions.

Moles of CS₂ = 19/76 = 0.25 mol. According to the equation, 1 mol CS₂ produces 2 mol SO₂. Therefore, 0.25 mol CS₂ forms 0.5 mol SO₂. Mass = 0.5 × 64 = 32 g.

Twenty-five grams equal 0.25 mole CaCO₃. The same amount of CO₂ occupies 5.6 dm³ at STP.

1.6 g oxygen equals 0.05 mole. Therefore, the number of molecules equals 0.05 × Avogadro's number.

One mole Pb(NO₃)₂ forms one mole PbO whose molar mass is 223 g.

Each mole KMnO₄ contains four moles oxygen atoms. Therefore, 0.25 mole contains one mole oxygen atoms.

Iron provides only 0.5 mole while sulfur provides 0.625 mole. Iron is present in the smaller stoichiometric amount.

Multiplication by Avogadro's number gives approximately 56 g mol⁻¹, the atomic mass of iron.