The conversions chemistry uses most

1 dm³ = 1000 cm³
1 kg = 1000 g, 1 tonne = 1000 kg
concentration (g/dm³) = mass (g) ÷ volume (dm³)

  1. 250 cm³ = 250 ÷ 1000 = 0.25 dm³
  2. 5.0 g in 250 cm³: 5.0 ÷ 0.25 = 20 g/dm³

Most wrong concentrations come from dividing by cm³ instead of dm³.

Figures, powers and ratios

  • Give answers to the significant figures asked, usually the fewest used in the data.
  • Very big and very small numbers go in standard form: 3 mol of particles is 3 × 6.02 × 10²³ = 1.81 × 10²⁴.
  • The big numbers in a balanced equation are a mole ratio: in N₂ + 3H₂ → 2NH₃, 3 mol of H₂ makes 2 mol of NH₃.

cm³ and dm³