In this experiment you will determine the value of y in the formula for hydrated barium chloride, BaCl2.yH2O. You will do this by measuring the mass loss when a sample of hydrated barium chloride is heated. BaCl2.yH2O(s) → BaCl2(s) + yH2O(g) FA 5 is hydrated barium chloride, BaCl2.yH2O.

1. (a)Method Before starting any practical work, read through all the instructions and prepare a table for your results in the space provided. • Weigh the crucible with a lid and record the mass. • Add all the FA 5 to the crucible. • Reweigh the crucible with the lid and FA 5. Record the mass. • Place the crucible in the pipe-clay triangle on top of a tripod. • Heat the crucible gently with the lid on for about 1 minute. • Remove the lid and then heat more strongly for a further 4 minutes. • Replace the lid and allow the crucible to cool. • While the crucible is cooling you may wish to begin work on Question 3. • Once the crucible has cooled, reweigh the crucible with the lid and contents. Record the mass. • Calculate and record the mass of FA 5 used, the mass of the residue and the mass of water lost. I II III IV V[5]
2. (b)(i)Calculate the number of moles of barium chloride in the residue. You may assume all the water has been removed. moles of BaCl2 = ............................ mol[1]
3. (b)(ii)Calculate the number of moles of water lost. moles of H2O lost = ............................ mol[1]
4. (b)(iii)Calculate the value of y in BaCl2.yH2O. y = ............................[1]
5. (c)(i)For this experiment to give an accurate value for y, anhydrous barium chloride must be thermally stable. Explain fully what would happen to the value of y if BaCl2 were to decompose slightly during heating.[2]
6. (c)(ii)Starting with the same mass of hydrated barium chloride, suggest how you could modify the experiment to determine more accurately the mass of water lost.[1]