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CIE Jun 2016 v2 Paper 2 Q3
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![Acidified potassium dichromate(VI) can oxidise ethanedioic acid, H2C2O4. The relevant half-equations are shown. Cr2O7 2 + 14H+ + 6e2Cr3+ + 7H2O H2C2O42CO2 + 2H+ + 2e PMT (a) State the overall equation for the reaction between acidified dichromate(VI) ions and ethanedioic acid.[2] (b) In an experiment a 0.242 g sample of hydrated ethanedioic acid, H2C2O4.xH2O, was reacted with a 0.0200 mol dm3 solution of acidified potassium dichromate(VI). 32.0 cm3 of the acidified potassium dichromate(VI) solution was required for complete oxidation of the ethanedioic acid. (i) Calculate the amount, in moles, of dichromate(VI) ions used to react with the sample of ethanedioic acid. (ii) Calculate the amount, in moles, of ethanedioic acid in the sample. amount =mol [1] (iii) Calculate the relative molecular mass, Mr, of the hydrated ethanedioic acid. amount =mol [1] (iv) Calculate the value of x in H2C2O4.xH2O. Mr =[1] x =[1] [Total: 6]UCLES 2016 9701/22/M/J/16 [Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/June_2016_v2_QP_-_Paper_2_CIE_Chemistry_A-level_3.jpg)
![Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A LevelMay/June 2016 9701 22 Question Answer Mark Total PMT (iii) 2HP (or 2HI)(or ) H2 + P2 (or I 2) [1] [1] (iv) Ag (aq) + Q (aq) (or Cl ) AgQ(s) (or AgCl(s)) AgQ(s) / AgCl(s) + 2NH3(aq)Ag(NH3)2 (aq) + Q (aq) / Cl (aq) (d) (i) no of Cl increases by one each time / matches group number due to increasing number of valence/outer(most/shell) electrons / oxidation number / valency (of Mg, Al , Si) (ii) MgCl 2 (+aq)Mg + 2Cl 2+ AlCl 3 + 6H2OAl(H2O)6 + 3Cl 3+ / Al(H2O)5(OH) 2+ + H + 3Cl SiCl 4 + 2H2OSiO2 + 4H + 4Cl (a) Cr2O7 + 8H + 3H2C2O42Cr + 6CO2 + 7H2O 2 3+ M1 = species M2 = balancing (b) (i) (0.0232.0/1000 =) 6.4010 4 (ii) (6.4103 = )1.9210 4 3 (iii) (iv) (0.242 / 1.9210 3 =) 126(.0) (12690 = 36; 36 / 18 = 2 hence) x = 2Cambridge International Examinations 2016 [1] [1] [1] [1] [1] [1] [1] [2] [2] [3] [Total 21] [1] [1] [2] [1] [1] [1] [1] [1] [1] [1] [1] [Total 6]<br />](https://learnah.org/wp-content/uploads/2018/08/June_2016_v2_MS_-_Paper_2_CIE_Chemistry_A-level_3.jpg)