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CIE Jun 2015 v2 Paper 4 Q3
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![(a) Complete the table with the symbol of the ion that contains the number of protons, electrons and neutrons stated in the following table. Therst line has been completed as an example. protons electrons neutrons symbol 15 16 18 7Li+ [2] (b) Describe and explain the trend in the solubilities of the sulfates of the Group II elements down the group.[4] (c) Calcium sulfate is sparingly soluble in water. Describe and explain what you would see when a few cm3 of concentrated Na2SO4(aq) were added to a saturated solution of CaSO4(aq).[2] (d) When a solution of a chromium salt X is electrolysed, chromium metal is deposited on the cathode, according to the following equation. Crn+(aq) + neCr(s) When a current of 1.8 A was passed for 40 minutes through a solution of salt X, it was found that 0.776 g of chromium had been deposited. Calculate the value of n in the above equation. Show your working.UCLES 2015 9701/42/M/J/15 n =[4] [Total: 12] [Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/June_2015_v2_QP_-_Paper_4_CIE_Chemistry_A-level_3.jpg)
![Page 4 Cambridge International A LevelMay/June 2015 Mark Scheme Syllabus Paper 9701 42 [2] [4] [2] [4] [Total: 12] (a) 33 P (b) Solubility decreases (from Mg to Ba or down the group) Both lattice energy / Hlatt and enthalpy change of hydration / Hhyd are involved enthalpy change of hydration decreases more than lattice energy So enthalpy change of solution / positive or less exothermic or less negative (NOT Hsol decreases, or increases) Hsol becomes more endothermic or more (c) precipitate / solid CaSO4 would form due to the common ion effect or Ksp is exceeded or the following equilibrium shifted over to the right Ca aq) + SO4 (aq)CaSO4(s) 2+( (d) charge passed = 1.840 x 60 (= 4320 C) n(e ) n(Cr) = 4320 / 96500 (= 4.47710 2 mol) ecf = 0.776 / 52 (= 1.49210 2 mol) ecf = 4.47710 2 / 1.49210 2 = 3.00 (=3)Cambridge International Examinations 2015<br />](https://learnah.org/wp-content/uploads/2018/08/June_2015_v2_MS_-_Paper_4_CIE_Chemistry_A-level_3.jpg)