Mole Calculations IGCSE Chemistry: Formulas, Steps and Practice
Mole calculations are one of the most searched IGCSE Chemistry topics because they appear in almost every paper and many students find them tricky. With a clear method and practice, you can gain the marks that separate an A from an A*.
Essential Mole Formulas for IGCSE
- Moles and mass: (\text{moles} = \frac{\text{mass (g)}}{\text{Mr or Ar}})
- Moles and gas volume: (\text{moles} = \frac{\text{volume (dm}^3)}{24}) (at r.t.p.)
- Moles and solution: (\text{moles} = \text{concentration (mol/dm}^3) \times \text{volume (dm}^3))
- Reacting masses: Use the balanced equation; work in moles, then convert to mass or volume as required.
Always write the balanced equation and show your working so you can gain method marks.
Common Question Types
- Mass to moles and moles to mass using Mr.
- Concentration and volume of solutions.
- Reacting mass – “What mass of X is needed to make Y?”
- Percentage yield and percentage purity (moles first, then ratio).
Practise with past paper mole questions and mark with the mark scheme so you learn the exact wording and units examiners expect.
Step-by-Step: Tackling a Typical Mole Question
Example: “What mass of oxygen is needed to react completely with 24 g of magnesium?” (2Mg + O₂ → 2MgO.) Step 1: Moles of Mg = mass/Mr = 24/24 = 1 mol. Step 2: From the equation, 2 mol Mg need 1 mol O₂, so 1 mol Mg needs 0.5 mol O₂. Step 3: Mass of O₂ = moles × Mr = 0.5 × 32 = 16 g. Always write the balanced equation, show each step, and give the unit. Common errors: Using Ar instead of Mr for a compound; wrong ratio from the equation; forgetting to convert between mass and moles. Practise until you can do these without hesitation.
Tutopiya Resources and Free Trial
Tutopiya’s Chemistry tutors specialise in mole calculations and can give you step-by-step practice and feedback until you are confident.
Book a free trial with an IGCSE Chemistry tutor or explore Tutopiya’s learning portal for free resources and calculation practice.
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