Edexcel Jan 2012 Paper 2 Q19 (with explained solutions) |

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Edexcel Jan 2012 Paper 2 Q19

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PMT 19 The carbonates of Group 2 in the Periodic Table decompose on heating to form the corresponding metal oxide and carbon dioxide. A general equation for the reaction is MCO3(s) (cid:111) MO(s) + CO2(g) The thermal stability of these carbonates can be compared in the laboratory using the apparatus in the diagram below. The test tube on the left contains a sample of a metal carbonate and the tube on the right contains limewater. test tube metal carbonate heat limewater (a) (i) State the measurement that you would make in this experiment. (1)(ii) Suggest three ways to make sure that, when carrying out this experiment, the thermal stabilities of the different carbonates are compared fairly. (3) 12310 *P39303A01024*<br />
PMT (b) (i) State the trend in the thermal stability of the metal carbonates as the group is descended. (1)*(ii) Explain this trend in stability. (3)(Total for Question 19 = 8 marks) *P39303A01124* 11 Turn over<br />

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Mark Mark Question Number 19(a)(i) Acceptable Answers Reject How fast/how quickly Time for the first (permanent) cloudiness to appear in the limewater ALLOW Time for the limewater to turn milky/cloudy ALLOW Time for the limewater to turn milky/cloudy and (ppt) to dissolve ALLOW how long for time IGNORE references to volume of CO2 Reject Constant temp/ heat Water bath Fixed angle Volume/quantity Concentration / quantity Acceptable Answers Question Number 19(a)(ii) Any three from Constant Bunsen flame/electrical heater setting Fixed height of test tube above the flame Fixed moles/(ALLOW mass/amount) of carbonate Fixed volume/amount/mass of limewater Penalise use of quantity once only Same surface area/particle size (of solid) Standardise cloudiness of limewater using the disappearance of a cross (or similar) IGNORE repeats & use same measuring instruments /same person 6CH0201 1201<br />
Question Number 19(b)(i) Acceptable Answers Reject Mark More stable/(thermal stability) increases (as the group is descended) Mark Acceptable Answers Question Number 19(b)(ii) Ignore an incorrect answer to 19b(i) Reject Atomic/metal radius/charge density of atom/ molecule and mark statements given independently Cation/positive (ALLOW metal) ion becomes larger (charge unchanged) OR cation charge density reduced (1) IGNORE references to shielding Polarisation/distortion reduced (1) (ALLOW polarising power reduced) of carbonate electron cloud/ carbonate ion/C-O bonds /anion (1) OR reverse argument for stability decreasing as group ascended 6CH0201 1201<br />
Acceptable Answers Reject Throughout 20 (a): IGNORE sf except 1 sf (penalise once) correct answer with no working scores full marks mark consequentially IGNORE units unless incorrect 0.109 x 27.35 x 103 (1) = 2.98115 x 103 (mol) = 2.98 x 103 / 0.00298(mol) 0.003 (1) cq only on some concentration x some volume Acceptable Answers Reject Moles I2 = 0.5 x moles thiosulfate = 0.5 x answer to (a)(i) = 1.490575 x 103 = 1.49 x 103 /0.00149(mol) Acceptable Answers Reject Moles of Cl2 = moles of I2 = answer to (a)(ii) = 1.49 x 103 /0.00149(mol) Mark Mark Mark Question Number 20 (a)(i) Question Number 20 (a)(ii) Question Number 20 (a)(iii) 6CH0201 1201<br />

Question 19 20 21 22

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