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AQA GCSE · Question 09.2 · Quantitative chemistry
Calculate the percentage by mass of methanol in methylated spirit. Use Table 6.
Calculate the percentage by mass of methanol in methylated spirit. Use Table 6.
How to approach this question
1. Calculate the total mass of the methylated spirit sample by adding the masses of all the substances in Table 6.
2. Identify the mass of methanol from Table 6.
3. Use the formula for percentage by mass: (mass of component / total mass) × 100.
4. Substitute the values and calculate the result.
Full Answer
Total mass = 265.5 + 23.3 + 3.0 + 1.5 = 293.3 g
Mass of methanol = 23.3 g
Percentage by mass = (mass of methanol / total mass) × 100
Percentage = (23.3 / 293.3) × 100 = 7.944... %
Answer: 7.94 %
To calculate the percentage by mass of methanol, we need two values: the mass of methanol and the total mass of the mixture.
1. **Find the total mass:**
Total mass = Mass(Ethanol) + Mass(Methanol) + Mass(Pyridine) + Mass(Methyl violet)
Total mass = 265.5 + 23.3 + 3.0 + 1.5 = 293.3 g
2. **Find the mass of methanol:**
From the table, the mass of methanol is 23.3 g.
3. **Calculate the percentage:**
Percentage by mass = (mass of methanol / total mass) × 100
Percentage = (23.3 / 293.3) × 100
Percentage = 0.07944... × 100
Percentage = 7.944... %
Rounding to 3 significant figures gives 7.94%.
Common mistakes
✗ Forgetting to calculate the total mass and just dividing by the mass of ethanol.
✗ Calculation errors when adding the masses.
✗ Forgetting to multiply by 100.
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