GCSE chemistry calculations
Most chemistry calculations come down to a few steps: Mr, moles, the ratio from the equation, then back to mass.
Relative formula mass
Add the relative atomic masses of every atom in the formula. Brackets multiply everything inside them.
| Formula | Working | Mr |
|---|---|---|
| H₂O | 2 × 1 + 16 | 18 |
| CO₂ | 12 + 2 × 16 | 44 |
| Ca(OH)₂ | 40 + 2 × (16 + 1) | 74 |
Moles and reacting masses
Moles = mass ÷ Mr. Balance the equation first: its numbers give the ratio of moles that react.
Concentration and rates
Concentration is the amount dissolved per volume. A mean rate of reaction is the amount used or made divided by the time taken.
Printable calculations workbookIn the Shop Questions
Why do I get the wrong answer even when my method is right?
Check the units first: grams against kilograms, cm³ against dm³. Then check that the equation is balanced.
Related
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