Practice Questions

The mole ratio Na : NaCl is 1:1. Therefore, 0.5 moles of Na produce 0.5 moles of NaCl. Mass = 0.5 × 58.5 = 29.25 g.

Moles of CO₂ = 88 ÷ 44 = 2.0 moles. Molecules = 2.0 × 6.022 × 10²³ = 1.2044 × 10²⁴.

Moles of O₂ = 64 g ÷ 32 g/mol = 2.0 moles. At STP, molar volume is 22.4 dm³. Therefore, volume = 2.0 × 22.4 = 44.8 dm³.

The mole ratio of O₂ to CH₄ is 2:1. For 2.5 moles CH₄, moles of O₂ = 2.5 × 2 = 5.0 moles. At STP, 1 mole of gas occupies 22.4 dm³, so volume = 5.0 × 22.4 = 112.0 dm³.

1.6 g O₂ = 0.05 mol. Molecules = 0.05 × 6.022 × 10²³ = 3.011 × 10²².

One mole Pb(NO₃)₂ forms one mole PbO. Molar mass PbO = 207 + 16 = 223 g.

One mole KMnO₄ contains four moles oxygen atoms. Thus only 0.25 mol KMnO₄ contains one mole oxygen atoms.

Iron = 0.5 mol, sulphur = 0.625 mol. Since the reaction ratio is 1:1, iron limits the reaction.

Multiplying by Avogadro's number gives approximately 56 g/mol, corresponding to iron.

One mole pentane forms 5 CO₂ + 6 H₂O = 11 mol products. Therefore 0.25 mol forms 2.75 mol products.