G2 Science Chemistry Formula List
G2 Science Chemistry calculation relationships with units, reacting ratios, worked examples and the correct course scope.
On this page
A calculation and formula reference for G2 Science Chemistry (K223 / K225). Read the relationship, units and condition together. The balanced equation controls a reacting ratio; a formula subscript controls the composition of one particle.
Mass, amount and chemical formulae
| Relationship | Symbols and units | When to use it |
|---|---|---|
| Mᵣ = ∑ Aᵣ | Mᵣ and Aᵣ have no unit | Include every subscript and bracket multiplier in the formula. |
| n = m/M; m = nM | n mol, m g, M g/mol | Match the mass unit to the molar-mass unit; this does not require a reaction ratio. |
| mean Aᵣ = ∑(A_(r,i) fᵢ) | Fractional isotope abundance fᵢ has no unit; ∑ fᵢ = 1 | For percentage abundances, divide each percentage by 100. |
| total positive charge + total negative charge = 0 | Ionic charges in units of elementary charge | Choose the smallest whole-number ion ratio; never change an ion’s own formula. |
| CₙH₂ₙ₊₂; CₙH₂ₙ | n is the number of carbon atoms | Acyclic alkanes / acyclic alkenes with one double bond; not all hydrocarbons. |
Reaction patterns to recognise
These patterns help identify products; they are not balanced equations. Write the species and balance atoms and charge for the actual reaction.
- Dilute non-oxidising acid + suitably reactive metal → salt + hydrogen.
- Acid + metal oxide or hydroxide → salt + water.
- Acid + carbonate → salt + water + carbon dioxide.
- Complete hydrocarbon combustion → carbon dioxide + water.
A quick application: mass to moles
For 8.00 g of NaOH, M = 23.0 + 16.0 + 1.0 = 40.0 g/mol. Therefore n = m/M = 8.00/40.0 = 0.200 mol. The unit g cancels against g/mol; the answer is an amount, not a mass.
G2 stopping point
Reacting-mass stoichiometry and gas-volume calculations are not required. Neither are R_f values or calculating pH from hydrogen-ion concentration. Use chromatogram comparisons and indicator/pH descriptions qualitatively.
Find the explanation behind a relationship on the course hub, then use the topic check with this sheet closed.