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CIE Jun 2015 v2 Paper 4 Q2
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![(a) A sample of lead consists of the following isotopes in the percentage abundances stated. isotope % abundance 204Pb 206Pb 207Pb 208Pb 1.9 24.8 21.4 51.9 Use these data to calculate the relative atomic mass of the sample of lead to two decimal places. Ar (Pb) =[2] (b) Tin and lead both form oxides in oxidation states (II) and (IV). (i) How does the acid-base nature of tin(II) oxide compare to that of tin(IV) oxide?[1] (ii) Illustrate your answer to (i) with equations, showing the reaction of each oxide with a suitable acid or base, as appropriate. SnOSnO2[2] (iii) Describe the reactions, if any, that occur when separate samples of tin(IV) oxide and lead(IV) oxide are heated in air. Include any relevant observations and write equations for any reactions that occur.[3] [Total: 8]UCLES 2015 9701/42/M/J/15<br />](https://learnah.org/wp-content/uploads/2018/08/June_2015_v2_QP_-_Paper_4_CIE_Chemistry_A-level_2.jpg)
![Page 3 Cambridge International A LevelMay/June 2015 Mark Scheme Syllabus Paper 9701 42 (a) Ar = 2040.019 + 2060.248 + 207 = 207.21 The last answer written by the candidate needs to be written with 2 d.p. to get the last mark. (correct ans = [2]) [2] [1] [2] [3] [Total: 8] (b) (i) Tin(II) oxide is more basic than tin(IV) oxide or tin(II) oxide is less acidic than tin (IV) oxide (ii) e.g. SnO + 2HCl SnO2 + 2NaOHSnCl2 + H2O(or ionic or with H2SO4)Na2SnO3 + H2O (or ionic or with KOH etc.) (iii) SnO2 stays the same (white) or is stable or no reaction PbO2 changes colour (from brown/black to yellow/orange/red) PbO2PbO + O2 or 3PbO2Pb3O4 + O2Cambridge International Examinations 2015<br />](https://learnah.org/wp-content/uploads/2018/08/June_2015_v2_MS_-_Paper_4_CIE_Chemistry_A-level_2.jpg)