Pearson Edexcel IAL Chemistry 1.9 Yield & atom economy

Practise calculating percentage yield and atom economy from equations, product masses and laboratory or industrial process data.

Exam points

calculate percentage yield from actual mass and the theoretical mass from stoichiometry
find atom economy by comparing desired product mass with total product mass
interpret when co-products make an industrial route useful despite multiple products

[Maximum number: 2]

This question is about magnesium, magnesium oxide and magnesium sulfate.

Hydrated crystals of magnesium sulfate, $\mathrm{MgSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}$ , can be made by reacting magnesium with sulfuric acid.

In an experiment, magnesium was added to $30.0 \mathrm{~cm}^{3}$ of $0.500 \mathrm{~mol} \mathrm{dm}^{-3}$ sulfuric acid.
$\left[M_{\mathrm{r}}\right.$ value: $\mathrm{MgSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}=246.4 \quad A_{\mathrm{r}}$ value: $\left.\mathrm{Mg}=24.3\right]$

The magnesium sulfate solution was allowed to crystallise.

The crystals were dried and weighed.
The mass of the hydrated crystals, $\mathrm{MgSO}_{4} \cdot 7 \mathrm{H}_{2} \mathrm{O}$ , was 2.78 g .
Calculate the percentage yield in this experiment.

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1.9—Percentage yields and percentage atom economies (by mass) in laboratory and industrial processes question 1