A student investigated the purity of a sample of magnesium chloride, MgCl₂ - Scottish Highers Chemistry - Question 10 - 2019

The correct order is:

E → C → B → D → A

This sequence involves first weighing the filter paper, then filtering the precipitate, washing it to remove impurities, drying it in an oven, and finally weighing the precipitate along with the filter paper.

To find the mass of magnesium chloride, we need to use the molar masses and the stoichiometry of the reaction:

1. Calculate the moles of silver chloride: $ext{Moles of AgCl} = \frac{1.393 ext{ g}}{143.4 ext{ g/mol}} = 0.0097 ext{ mol}$

2. From the balanced equation, the molar ratio of MgCl₂ to AgCl is 1:2. Therefore, the moles of MgCl₂ produced are: $\text{Moles of MgCl₂} = \frac{0.0097}{2} = 0.00485 ext{ mol}$

3. Calculate the mass of magnesium chloride: $\text{Mass of MgCl₂} = 0.00485 ext{ mol} \times 95.3 ext{ g/mol} = 0.461 ext{ g}$

To calculate the percentage of magnesium chloride in the original impure sample, we use the formula:

$\text{Percentage} = \left( \frac{\text{mass of MgCl₂}}{\text{mass of impure sample}} \right) \times 100$

Substituting in the values:

$\text{Percentage} = \left( \frac{2.403 ext{ g}}{2.503 ext{ g}} \right) \times 100 = 96.0\%$