A known mass of hydrated magnesium sulfate, MgSO4 .xH2 O, was dissolved in water. Excess aqueous barium chloride was added. The precipitate of barium sulfate was fi ltered, washed and dried. Finally it was weighed. Mass of hydrated magnesium sulfate = 1.476 g Mass of barium sulfate formed = 1.398 g The mass of one mole of BaSO4 = 233 g The number of moles of BaSO4 formed = ............... [1] The number of moles of MgSO4 .xH2 O = ............... [1] The mass of one mole of MgSO4 .xH2 O = ...............g [1 The mass of one mole of MgSO4 = 120 g The mass of xH2 O in one mole of MgSO4 .xH2 O = ............... [1] x = ............... [1] [Total: 15] Save My Exams! – The Home of Revision For more awesome GCSE and A level resources, visit us at www.savemyexams.co.uk/ 5 Thallium is a metal in Group III. It has oxidation states of +1 and +3. (a) Give the formula for the following thallium compounds. (i) thallium(I) sulfi de .................................................................................................. [1] (ii) thallium(III) chloride ............................................................................................. [1] (b) Thallium(I) chloride is insoluble in water. Complete the description of the preparation of a pure sample of this salt. Step 1 Mix a solution of sodium chloride with thallium(I) sulfate solution. A white precipitate forms. Step 2 ..................................................................................................................................... [1] Step 3 ..................................................................................................................................... [1] Step 4 ..................................................................................................................................... [1] (c) When thallium(I) chloride is exposed to light, a photochemical reaction occurs. It changes from a white solid to a violet solid. (i) Name another metal halide which changes colour when exposed to light. Give the major us