Chemical formulae, equations and calculations

Worked examples (6)

• 1How does an alkali metal react? (Getting started)
• 2Order Group 1 and Group 7 by reactivity (Getting started)
• 3Explain the Group 1 reactivity trend (Building confidence)
• 4Predict a halogen displacement reaction (Building confidence)
• 5Explain the Group 7 reactivity trend (Stretch)
• 6Deduce a reactivity order from results (Stretch)

Model answers (6)

• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style — extended
• ✓Model answer — 4WSD0/1C style — extended

Worked examples (6)

• 1Write a word equation from a description (Getting started)
• 2Deduce a formula from ion charges (Getting started)
• 3Balance the combustion of methane (Building confidence)
• 4Balance a displacement reaction (Building confidence)
• 5Balance ethane combustion (fraction then double) (Stretch)
• 6Build a full symbol equation with state symbols (Stretch)

Model answers (6)

• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style — extended
• ✓Model answer — 4WSD0/1C style — extended

Worked examples (6)

• 1Plug-in percentage yield (Getting started)
• 2Explain why yield is below 100% (Getting started)
• 3Find the theoretical yield, then the percentage yield (Building confidence)
• 4Find the actual yield from a given percentage yield (Building confidence)
• 5Work backwards to find the starting mass needed (Stretch)
• 6Full reacting-mass to percentage yield (Stretch)

Model answers (6)

• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style — extended
• ✓Model answer — 4WSD0/1C style — extended

Worked examples (6)

• 1Relative formula mass of compounds (Getting started)
• 2Moles from mass with n = m ÷ Mr (Getting started)
• 3Mass and number of particles in a sample (Building confidence)
• 4Reacting mass with a 1 : 1 ratio (Building confidence)
• 5Reacting mass with a non-1 : 1 ratio (Stretch)
• 6Limiting reactant and mass of product (Stretch)

Model answers (6)

• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style — extended
• ✓Model answer — 4WSD0/1C style — extended

Worked examples (6)

• 1Find the mass of oxygen that combined (Getting started)
• 2Empirical formula of magnesium oxide (Getting started)
• 3Empirical formula of copper oxide (Building confidence)
• 4Empirical formula with a non-1:1 ratio (Building confidence)
• 5Empirical formula of an unknown metal sulfide (Stretch)
• 6Explain the experimental design (Stretch)

Model answers (6)

• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style — extended
• ✓Model answer — 4WSD0/1C style — extended

Worked examples (6)

• 1Classify empirical vs molecular formulae (Getting started)
• 2Empirical formula from a mass ratio (Getting started)
• 3Empirical formula from percentages (Building confidence)
• 4Empirical formula needing ×2 scaling (Building confidence)
• 5Molecular formula from empirical formula and Mr (Stretch)
• 6Empirical formula from combustion data (Stretch)

Model answers (6)

• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style — extended
• ✓Model answer — 4WSD0/1C style — extended

Worked examples (6)

• 1Find the mass of oxygen from the mass change (Getting started)
• 2State the formula from a given mole ratio (Getting started)
• 3Reduction of a copper oxide — find the formula (Building confidence)
• 4Oxidation of magnesium — find the formula (Building confidence)
• 5Unknown metal oxide from raw masses (Stretch)
• 6Explain a step in the reduction method (Stretch)

Model answers (6)

• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style — extended
• ✓Model answer — 4WSD0/1C style — extended

Worked examples (6)

• 1Classify an atom: lose or gain? (Getting started)
• 2Charge of a metal ion from its group (Getting started)
• 3Electrons gained by a non-metal (Building confidence)
• 4Write an electron-transfer equation (Building confidence)
• 5Count protons and electrons in an ion (Stretch)
• 6Predict ion charges across the table (Stretch)

Model answers (6)

• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style
• ✓Model answer — 4WSD0/1C style — extended
• ✓Model answer — 4WSD0/1C style — extended