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CIE Jun 2013 v2 Paper 4 Q2
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![Examiners For Use (a) (i) With the aid of a fully-labelled diagram, describe the standard hydrogen electrode. (ii) Use the Data Booklet to calculate the standard cell potential for the reaction between Cr2+ ions and Cr2O7 2 ions in acid solution, and construct a balanced equation for the reaction. =V equation(iii) Describe what you would see if a blue solution of Cr2+ ions was added to an acidi ed solution of Cr2O7 2 ions until reaction was complete.[8]UCLES 2013 9701/42/M/J/13<br />
Examiners For Use (b) A buffer solution is to be made using 1.00 mol dm3 ethanoic acid, CH3CO2H, and 1.00 mol dm3 sodium ethanoate, CH3CO2Na. Calculate to the nearest 1 cm3 the volumes of each solution that would be required to make 100 cm3 of a buffer solution with pH 5.50. Clearly show all steps in your working. Ka (CH3CO2H) = 1.79105 mol dm3 volume of 1.00 mol dm3 CH3CO2H =cm3 volume of 1.00 mol dm3 CH3CO2Na =cm3 [4] (c) Write an equation to show the reaction of this buffer solution with each of the following. (i) (ii) added HCladded NaOH[2] (d) Choose one reaction in organic chemistry that is catalysed by an acid, and write the structural formulae of the reactants and products in the boxes below. H+ [3] [Total: 17]UCLES 2013 9701/42/M/J/13 [Turn over<br />](https://learnah.org/wp-content/uploads/2018/08/June_2013_v2_QP_-_Paper_4_CIE_Chemistry_A-level_2-0.jpg)
![Page 4 Mark Scheme Syllabus Paper GCE A LEVELMay/June 2013 9701 42 (a) (i) hydrogen gas at 1 atm PMT Pt -3 /HCl at 1 mol dm and 298K platinum electrode in contact with solution, with H2 bubbling over it [1] H2(g) going in (i.e. not being produced) [1] solution at 1 mol dm 3 (or 0.5 M if H2SO4) and T=298 K, p=1 atm [1] or HCl or H2SO4 [1] (ii) E = 1.33(-0.41) = 1.74 V 2- 2+ 3+ Cr2O7 + 14H + 6Cr8Cr + 7H2O (iii) Colour would change from orange to green [1] [1] [1] [1] [8] (b) there are two ways of calculating the ratio: pKa = log10(Ka) = log10(1.79 x 10 ) = 4.747 (4.75) or [H ] = 10 = 3.16 x 10 [1] 5 -5.5 -6 log10([B] / [A]) = pHpKa = 0.753 (0.75) or [salt] / [acid] = Ka / [H [1][B] / [A] = 10 = 5.66 0.753 or = 1.79 x 10 / 3.16 x 10 = 5.66 5 6 (or [A] / [B] = 0.177) (correct ratio = [3] marks) [1] since B + A = 100, (100A) / A = 5.66vol of acid = 15 cm vol of salt = 85 cm [1] [4]Cambridge International Examinations 2013<br />
Page 5 Mark Scheme Syllabus Paper GCE A LEVELMay/June 2013 9701 42 (c) (i) CH3CO2Na + HClCH3CO2H + NaCl (ii) CH3CO2H + NaOHCH3CO2Na + H2O PMT [1] [1] [2] (d) e.g. hydrolysis of esters RCO2R' (+ H2O)RCO2H + R'OH or its reverse or hydrolysis of amides: RCONH2 (+ H3O )RCO2H + NH4 hydrolysis of nitriles: RCN (+ H3O + H2O)RCO2H + NH4 nitration of benzene (or any arene): C6H6 + HNO3C6H5NO2 (+ H2O) dehydration of alcohols, e.g. : CH3CH(OH)CH3CH3CH=CH2 + H2O (or the reverse) halogenation of ketones, e.g. : CH3COCH3 + X2CH3COCH2X (+ HX) [3] [Total: 17] (a) (i) HNO3 + H2SO4 conc (both acids) and 30 C < T < 60 C or warm (ii) dilute HNO3 or HNO3(aq) and room temp. (allow T30 C) (b) (allow intermediate from methylbenzene) NO (c) Sn/tin (or SnCl 2, Fe) + HCl (NOT H2SO4 or H , Zn, or LiAlH4.) [1] [1] [1] [3] [1] [1] [1] [1]Cambridge International Examinations 2013<br />](https://learnah.org/wp-content/uploads/2018/08/June_2013_v2_MS_-_Paper_4_CIE_Chemistry_A-level_2-0.jpg)
