CIE Nov 2015 v4 Paper 3 Q2

Answers available below

In this experiment you will determine the relative atomic mass of magnesium by thermal decomposition of hydrated magnesium sulfate. MgSO4.7H2O(s)MgSO4(s) + 7H2O(g) PMT FB 4 is hydrated magnesium sulfate, MgSO4.7H2O. (a) Method Record all your weighings in the space below.Weigh the crucible with its lid. Transfer all FB 4 into the crucible. Weigh the crucible, lid and FB 4. Place the crucible on the pipe-clay triangle. Heat the crucible gently with the lid on, for about one minute. Then heat the crucible strongly, without the lid, for a further four minutes. Leave the crucible and its contents to cool with the lid on, for several minutes. While the crucible is cooling, begin work on Question 3. When the crucible has cooled, weigh it, with the lid and contents. Calculate and record the mass of anhydrous magnesium sulfate produced and the mass of water lost. II III [3] (b) Calculations (i) Calculate the number of moles of water lost during heating. (Use the data in the Periodic Table on page 12.) (ii) Use the equation above and your answer to (i) to calculate the number of moles of anhydrous magnesium sulfate produced. moles of H2O =molUCLES 2015 9701/34/O/N/15 [Turn over moles of MgSO4 =mol<br /> (iii) Use your weighings and your answer to (ii) to calculate the relative formula mass, Mr, of anhydrous magnesium sulfate. PMT (iv) From your answer to (iii), calculate the relative atomic mass, Ar, of magnesium. Mr of MgSO4 =Ar of Mg =[4] (c) (i) How could the experiment be improved to ensure that the magnesium sulfate had been completely dehydrated?(ii) Why is the lid put on the crucible during cooling?[2] [Total: 9]UCLES 2015 9701/34/O/N/15<br />

Show answer