A student attempts to determine the percentage by mass of magnesium chloride in the solid mixture containing magnesium chloride, MgCl2, and anhydrous magnesium nitrate, Mg(NO3)2, using the following method. step 1 Accurately weigh about 1.5g of the solid mixture and record the mass. step 2 Dissolve the solid mixture in distilled water. step 3 Add an excess of silver nitrate solution. step 4 Filter the solid mixture and wash the precipitate collected with distilled water. step 5 Dry the precipitate in an oven. step 6 Weigh the precipitate and record the mass. In this process only the chloride ions from the magnesium chloride form a precipitate with the silver nitrate solution. MgCl2(aq) + 2AgNO3(aq) → Mg(NO3)2(aq) + 2AgCl(s) One student in the class obtains the following results. mass of solid mixture = 1.52 g mass of AgCl solid after drying = 3.63 g

1. (a)(i)Calculate the amount, in mol, of magnesium chloride present in the sample. amount of magnesium chloride = ................................... mol[1]
2. (a)(ii)Use your answer to (i) to calculate the percentage by mass of magnesium chloride in the sample. (If you were unable to answer (i) use 0.0102 mol. This is not the correct answer.) percentage by mass = ...................................[2]
3. (b)(i)Suggest what the student could do in step 2 to ensure the solid dissolves as quickly as possible.[1]
4. (b)(ii)Explain why the precipitate was washed with distilled water before it was dried.[1]
5. (b)(iii)Suggest why the precipitate is dried in an oven and not by direct heating with a Bunsen burner.[1]
6. (c)(i)In step 1, a small beaker was weighed, using a balance accurate to two decimal places, and its mass recorded. The sample was placed in the beaker and the mass of the beaker increased by 1.52 g. Calculate the percentage error in measuring the mass of this sample. Show your working. percentage error = ...................................[1]
7. (c)(ii)Other than by changing the balance, state how this percentage error could be reduced.[1]
8. (c)(iii)State what could be done in step 5 to ensure that the precipitate was completely dried.[1]
9. (d)Another student in the class did not dry their silver chloride. State how this would affect the value of the percentage by mass of magnesium chloride in the sample. Explain your answer.[1]