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OCR A Jun 2014 Paper 1 Q6
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![10 PMT This question is about Group 2 elements and compounds. (a) Group 2 carbonates undergo thermal decomposition. (i) Write the equation for the thermal decomposition of calcium carbonate. Include state symbols.[1] (ii) Write the formula of the Group 2 carbonate which decomposes at the highest temperature.[1] (b) Hydrated strontium chloride, SrCl26H2O, has a molar mass of 266.6 g mol1. A student heats 5.332 g of SrCl26H2O. The SrCl26H2O loses some of its water of crystallisation forming 3.892 g of a solid product. Use the information above to determine the formula of the solid product. Show your working. formula of solid product =[3]OCR 2014<br />
11 PMT (c) A chemist carries out reactions of barium and barium nitride, Ba3N2. Reaction 1 Barium is reacted with water. Reaction 2 Reaction 3 Barium nitride is reacted with water, forming an alkaline solution and an alkaline gas. Barium is reacted with an excess of oxygen at 500C, forming barium peroxide, BaO2. (i) Write equations for Reaction 1 and Reaction 2. Ignore state symbols. Reaction 1:Reaction 2:[3] (ii) Predict the structure and bonding of Ba3N2.[1] (iii) BaO2 formed in Reaction 3 contains barium and peroxide ions. The peroxide ion has the structure [OO]2. Suggest a dot-and-cross diagram for BaO2. Show outer shell electrons only. [1] [Total: 10] END OF QUESTION PAPEROCR 2014<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_1_QP_JUN14_question_6-0.jpg)
![F321 Mark Scheme June 2014 Answer (i) CaCO3(s) (cid:198) CaO(s) + CO2(g) (cid:57) (a) (ii) BaCO3 OR RaCO3 (cid:57) Question 6 (a) (b) FIRST CHECK THE ANSWER ON THE ANSWER LINE IF answer = SrCl22H2O award 3 marks M1 Correctly calculates Mol of SrCl26H2O = (5.332 / 266.6) = 0.02 mol (cid:57) M2 Correctly calculates Mol of water given off [(5.3323.892)/18] = 0.08 mol (cid:57) M3 Correctly calculates 0.08/0.02 = 4 mol of water lost from one mol of SrCl26H2O Therefore Answer = SrCl22H2O (cid:57) (c) (c) (i) Reaction 1: Ba + 2H2O (cid:198) Ba(OH)2 + H2 (cid:57) Reaction 2: Ba3N2 + 6H2O (cid:198) 3Ba(OH)2 + 2NH3 Correct products (cid:57) Balancing (cid:57) (ii) Giant ionic (lattice) (cid:57) Mark Guidance ALLOW formula if seen as reactant in an equation IGNORE name Allow alternative methods eg M1 Correctly calculates mol of SrCl26H2O as 5.332/266.6 = 0.02(00) mol DO NOT ALLOW M1 if a second mass is divided by 266.6 M2 Correctly calculates molar mass of partially hydrated product as 3.892/ 0.02(00) = 194.6 M3 Correctly calculates mass of H2O present as 194.6158.6 = 36.0 AND product is SrCl22H2O ALLOW ECF for the third mark for showing 158.6 taken from an incorrect stated molar mass leading to an ECF formula OR ALLOW 266.6194.6 = 72.0 to find amount of water lost Ignore state symbols ALLOW Giant lattice with ionic bonds ALLOW Giant ionic bonds DO NOT ALLOW atoms or molecules or dipoles 12<br />
F321 Mark Scheme June 2014 Answer OR OR OR 2+ 2+ 2+ 2+ x x x x Ba x x x x x x x x Ba x x x x x x x x Ba x x x x x x x x Ba x x x x Ox O x Ox O x Ox x Ox x 2- 2- 2- 2- Question (iii) Mark Guidance 2- ion 2 ion to have 12 electrons belonging to O atoms + 2 other Ba must have a 2+ charge Ba can be with or without octet. IGNORE lack of charge on O2 O2 electrons of another symbol. The 2 other electrons must match Ba if Ba has an octet. If O electrons are shown as 6 of one symbol and 6 of another, each O must have six electrons of the same symbol ALLOW OR 2+ 2+ x x x x Ba x x x x x x x x Ba x x x x Total 10 13 O x O x O x Ox 2- 2-<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_1_QP_JUN14_answer_6-0.jpg)
