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OCR A Jun 2016 Paper 1 Q4
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![10 This question is about the chemistry of the metals zinc, magnesium, aluminium and calcium. (a) Complete the electron configuration of a zinc atom. 1s2[1] (b) A sample of zinc was found to contain four isotopes with the abundances shown in the table. Isotope Abundance (%) 64Zn 66Zn 67Zn 68Zn 49.0 27.9 4.3 18.8 (i) Define the term relative atomic mass.[3] (ii) Calculate the relative atomic mass of zinc in this sample. Give your answer to two decimal places. relative atomic mass of zinc =[2]OCR 2016<br />
(c) Zinc carbonate, ZnCO3, reacts with dilute hydrochloric acid. 11 A student reacts a sample of ZnCO3 with an excess of dilute hydrochloric acid in a test-tube. (i) Describe what the student would see during this reaction.[1] (ii) Write the equation for the reaction between ZnCO3 and dilute hydrochloric acid.[1] (d) Magnesium will undergo redox reactions with aqueous salts of less reactive metals. (i) A student reacts magnesium with aqueous copper(II) sulfate. Mg(s) + CuSO4(aq) Cu(s) + MgSO4(aq) Explain, in terms of numbers of electron transferred, the redox processes taking place in this reaction.[2] (ii) The student also noticed that the magnesium started fizzing. The student thought the fizzing was due to the magnesium reacting with water in the mixture. Write the equation for the reaction of magnesium with water. Include state symbols.[2]OCR 2016 Turn over<br />
(e) A student reacts 35.0 cm3 of 3.00102 mol dm3 H2SO4(aq) with an excess of Al. 12 An equation for this reaction is shown. 2Al (s) + 3H2SO4(aq) Al2(SO4)3(aq) + 3H2(g) Calculate the mass, in g, of Al2(SO4)3 formed in solution. Give your answer to three significant figures. Show your working. mass =g [4] (f) Compounds of calcium have many uses. (i) Identify a compound of calcium that could be used to convert a soil pH from 5.8 to 7.5.[1] (ii) Calcium phosphide, Ca3P2, is an ionic compound used in rat poison. Calcium phosphide can be prepared by reacting calcium metal with phosphorus, P4. Write the equation for the reaction of calcium with phosphorus to form calcium phosphide.[1]OCR 2016<br />
(iii) Draw a dot-and-crossdiagram to show the bonding in calcium phosphide, Ca3P2. Show outer electrons only. 13 [2] [Total: 20] END OF QUESTION PAPEROCR 2016<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_1_QP_JUN16_question_4-0.jpg)
![F321 Question 4 4 (i) M1 (a) (b) Answer 1s2 2s2 2p6 3s2 3p6 3d10 4s2 (cid:51) The (weighted) mean mass of an atom (of an element) (cid:51) M2 Compared with 1/12th (the mass) (cid:51) M3 Of (one atom of) carbon-12 (cid:51) (b) (c) (ii) First check the answer line. If answer = 65.44 award 2 marks. (64 x 49.0) + (66 x 27.9) + (67 x 4.3) + (68 x 18.8) 100 OR 31.36(0) + 18.414 + 2.881 + 12.784 OR 65.439 (cid:51) = 65.44 (cid:51) (i) Effervescence OR fizzing OR bubbling OR gas produced AND The solid OR zinc carbonate would dissolve OR disappear (cid:51) 12 Mark Scheme June 2016 Mark Guidance ALLOW 4s2 3d10 ALLOW average for mean ALLOW mean mass of isotopes but DO NOT ALLOW mean mass of isotope (singular) DO NOT ALLOW mean mass of an element For M2 and M3 ALLOW compared with the mass of carbon-12 which is 12 ALLOW for three marks Mass of one mole of atoms Compared to 1/12th (mass of) one mole OR 12 g of carbon-12 ALLOW for three marks Mass of one mole of atoms 1/12th (mass of) one mole OR 12 g of carbon-12 ALLOW one mark for ECF from transcription error in the first sum provided the final answer is to two decimal places and is between 64 and 68 and is a correct calculation of the transcription ALLOW carbon dioxide produced DO NOT ALLOW incorrectly named gas eg H2<br />
June 2016 Guidance ALLOW multiples IGNORE state symbols IGNORE use of oxidation numbers if electron gain/loss is mentioned. Electrons gain/loss could be in half equations In the absence of text look for evidence on the equation ALLOW donated for lost Assume Cu refers to copper in CuSO4 ALLOW one mark two electrons gained and lost for each species but oxidation/reduction is incorrect or is omitted ALLOW one mark for correct oxidation and reduction if electron transfer is omitted and correct changes of oxidation state are shown (ie Mg 0 --> (+)2 AND Cu (+)2 to 0) ALLOW two electrons transferred from magnesium to copper ALLOW multiples ALLOW Mg(OH)2(s) ALLOW Mg(s) + H2O(g) OR H2O(l) --> MgO(s) + H2(g) including state symbols for one mark Mark Scheme Mark F321 Question 4 4 (c) (d) Answer (ii) ZnCO3 + 2HCl (cid:198) ZnCl2 + CO2 + H2O (cid:51) (i) Magnesium (atoms) has been oxidised AND Because it has lost two electrons (cid:51) Copper (ions) has been reduced AND Because it has gained two electrons (cid:51) (d) (ii) Mg(s) + 2H2O(l) (cid:198) Mg(OH) 2(aq) + H2(g) Correct reactants and products (cid:51) Balance and state symbols (cid:51) 13<br />
F321 Question 4 (e) Mark Scheme June 2016 Answer First check the answer line. If answer = 0.120 award 4 marks. M1 Mol of H2SO4 = 3.00 x 102 x 35.0 = 1.05 x 103 mol (cid:51) 1000 M2 Mol of Al2(SO4)3 = 1.05 x 103 = 3.5(0) x 104 mol (cid:51) 3 M3 = 342.3 (cid:51) M4 Mass Al2(SO4)3 = 3.5(0) x 104 x 342.3 and = 0.120 g (cid:51) Answer must be 3 sf OR CaO OR Calcium oxide (cid:51) (i) Ca(OH)2 OR Calcium hydroxide (f) (f) (ii) 6Ca + P4 (cid:198) 2Ca3P2 (cid:51) Guidance Mark ALLOW ECF ALLOW 0.00105 mol ALLOW 0.00035(0) mol ALLOW 342 DO NOT ALLOW 0.12 ALLOW Calcium carbonate OR CaCO3 ALLOW multiples IGNORE state symbols 14<br />
June 2016 Guidance For first mark: If 8 electrons are shown on the cation then the extra electron in the anion must match the symbol chosen for the electrons in the cation. IGNORE inner shells IGNORE circles ALLOW one mark if both electron arrangements and charges are correct but only one of each ion is drawn. ALLOW (brackets not required) 3[Ca2+] 3[Ca] 2+ [Ca2+]3 2[P3] 2[P]3- [P3-]2 DO NOT ALLOW [Ca3] 2+ [3Ca] 2+ [Ca]3 [P2]3 [2P]3 [P]2 3 2+ F321 Question (iii) Answer Mark Scheme Mark Ca with 8 (or no) electrons AND phosphide ion with dot- and-cross outermost octet (cid:51) Three Ca ions AND two phosphide ions with correct charges (cid:51) Total 20 15<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_1_QP_JUN16_answer_4-0.jpg)
