Moles and Avogadro’s Numbers

Sodium is an element consisting of atoms, so one mole contains Avogadro's number of atoms, not molecules. Concept tested: Representative particles.

At the same conditions of temperature and pressure, gas volumes follow mole ratios. One volume of O₂ produces two volumes of gaseous H₂O. Thus, 44.8 L O₂ forms 89.6 L H₂O(g). Concept tested: Gas volume ratios at STP.

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

Molecular formula is C₆H₁₂O₆ because 180/30 = 6. Thus each mole contains 12 moles hydrogen atoms.

Gas volumes follow mole ratios. Ratio N₂:H₂ = 1:3. Therefore 5 dm³ nitrogen requires 15 dm³ hydrogen.

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

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

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

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

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

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

One mole of CCl₄ contains 4 moles of Cl atoms. Thus 0.5 mol contains 2 mol Cl atoms.

From the ratio, 2 mol H₂S produce 3 mol S. Therefore, 1 mol H₂S produces 1.5 mol S. Mass = 1.5 × 32 = 48 g.

Urea contains two nitrogen atoms per molecule. Thus 0.5 mol nitrogen atoms correspond to 0.25 mol urea. Mass = 0.25 × 60 = 15 g.

10 g CaCO₃ = 0.1 mol. One mole CaCO₃ gives one mole CO₂. Therefore volume = 0.1 × 22.4 = 2.24 dm³.

The balanced equation shows equal coefficients for K and KOH, giving a simplified ratio of 1:1.

Benzene contains six carbon atoms in each molecule, so one mole contains six moles of carbon atoms.

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

16 g CH₄ = 1 mol. One mole methane requires two moles oxygen. Mass = 2 × 32 = 64 g.