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OCR A Jun 2012 Paper 1 Q4
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![4 Chlorine and its compounds have wide uses in chemistry. 10 (a) In drinking water, HClO kills bacteria. (i) Write an equation to show how HClO can form in drinking water.[1] (ii) Some scientists believe that chlorine compounds should not be present in drinking water. Suggest one reason why scientists may be worried by the presence of these compounds.[1] (b) Chlorine reacts directly with Group 2 elements to form chlorides that are very soluble in water. Aqueous chloride ions can be detected by adding aqueous silver nitrate. The appearance of solid silver chloride, AgCl, confirms the presence of chloride ions. (i) State the type of reaction that has taken place.[1] (ii) Write the ionic equation for this reaction. Include state symbols.[1] (c) A student is given a sample of an unknown Group 2 chloride.The student dissolves 2.86 g of the chloride in water. The student adds excess aqueous silver nitrate. 8.604 g of solid silver chloride, AgCl, forms. (i) Calculate the amount, in moles, of AgCl that forms. The molar mass of AgCl = 143.4 g mol1.OCR 2012 answer =mol [1]<br />
11 (ii) Deduce the amount, in moles, of the Group 2 chloride that the student dissolves. Hence deduce the relative atomic mass and the identity of the Group 2 metal. Give the relative atomic mass to one decimal place. You must show your working. relative atomic mass =Group 2 metal =[3] (d) Ammonium chloride, NH4Cl, is a salt which has covalent bonding, dative covalent (coordinate) bonding and ionic bonding. (i) What is a dative covalent (coordinate) bond?[1] (ii) Give the formulae of the ions present in NH4Cl.[1] (iii) Draw a dot-and-cross diagram to show the bonding in NH4Cl. Show the outer electrons only. TURN OVER FOR QUESTION 4(e)OCR 2012 [2] Turn over<br />
(e) A teacher heats potassium chlorate(V), KClO3. The equation is given below. 12 2KClO3(s) 2KCl(s) + 3O2(g) (i) This is an example of a redox reaction. What other type of reaction takes place?[1] (ii) The teacher heats 0.824 g of KClO3. Calculate the volume of oxygen produced, in cm3, measured at room temperature and pressure. Give your answer to the nearest whole number. answer =cm3 [3] [Total: 16] END OF QUESTION PAPER Copyright Information OCR is committed to seeking permission to reproduce all third-party content that it uses in its assessment materials. OCR has attempted to identify and contact all copyright holders whose work is used in this paper. To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced in the OCR Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download from our public website (www.ocr.org.uk) after the live examination series. If OCR has unwittingly failed to correctly acknowledge or clear any third-party content in this assessment material, OCR will be happy to correct its mistake at the earliest possible opportunity. For queries or further information please contact the Copyright Team, First Floor, 9 Hills Road, Cambridge CB2 1GE. OCR is part of the Cambridge Assessment Group; Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge.OCR 2012<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_1_QP_JUN12_question_4-0.jpg)
![F321 Mark Scheme June 2012 Marks Guidance ALLOW they OR chlorinated hydrocarbons OR it for chlorine compounds IGNORE harmful OR dangerous IGNORE references to HCl or HClO IGNORE chlorine is toxic DO NOT ALLOW chlorine is carcinogenic Equation AND state symbols required for mark DO NOT ALLOW spectator ions (i) Cl2 + H2O (cid:198) HClO + HCl (cid:57) Answer Question 4 (a) (ii) (Chlorine compounds are) carcinogenic OR (Chlorine compounds are) toxic OR poisonous (cid:57) (i) Precipitation (cid:57) (ii) Ag+(aq) + Cl(aq) (cid:198) AgCl(s) (cid:57) (b) (c) (i) 8.604/143.4 = 0.06(00) (mol) (cid:57) 11<br />
F321 Mark Scheme June 2012 Question (ii) (c) Answer If a Group 2 chloride is used amount of Group 2 chloride =0.0600 OR = 0.0300 mol (cid:57) Mass of 1 mol of Group 2 chloride = 2.86 = 95.3(3) (cid:57) 0.0300 [Relative atomic mass of M = 95.3(3)71.0) = 24.3 (g mol1)] AND metal = Mg (cid:57) Marks Guidance DO NOT ALLOW 24.3 and Mg without appropriate working Check to see if there is any ECF credit possible using working below ALLOW calculator value or rounding to 2 significant figures or more but IGNORE trailing zeroes, eg 0.200 allowed as 0.2 ALLOW ECF for correctly calculatedanswer to (c)(i) Must be at least 1 decimal place for second marking point ALLOW ECF for 2.86/mol of metal chloride seen above eg MCl will give 0.0600 mol of metal chloride and this will likely give 2.86/0.0600 = 47.7 eg MCl3 will give 0.0200 mol of metal chloride and this will likely give 2.86/0.0200 = 143.0 ALLOW ECF for mass of Group 2 chloride71.0 provided it is not a negative value ALLOW ECF even if molar mass of chloride was given as a whole number above ALLOW ECF for mass of metal chloride35.5 if amount of metal chloride = 0.0600 mol eg 47.735.5 = 12.2 AND Be ALLOW ECF for mass of metal chloride106.5 if amount of metal chloride = 0.0200 mol eg 143.0106.5 = 36.5 AND Ca 12<br />
Answer (i) A shared pair of electrons AND both electrons are donated by one atom (cid:57) Mark Scheme Marks F321 Question 4 (d) (ii) NH4 + AND Cl (cid:57) (iii) Ammonium ion with three covalent dot-and-cross bonds AND one dative covalent bond (cid:57) Chloride ion with 8e AND 1 of these electrons different (cid:57) Guidance June 2012 + + Cl + + Cl (cid:198) NH4Cl ALLOW NH4Cl (cid:198) NH4 OR NH4 ALLOW other symbols for dots and crosses eg triangles IGNORE charges IGNORE dative arrow within the lone pair of the N atom (e) (i) (Thermal) decomposition (cid:57) 13<br />
F321 Mark Scheme June 2012 Question Marks (e) (ii) FIRST CHECK THE ANSWER ON THE ANSWER LINE Answer If answer = 242 (cm3) award 3 marks (amount of KClO3) = 0.824/122.6 OR = 0.00672 (mol) (cid:57) (amount O2) = (mol of KClO3) 0.006723/2 OR = 0.0101 (mol) (volume of O2) = 0.010124 000 = 242 (cm3) (cid:57) Total 16 14 Guidance IGNORE over rounding to two significant figures once DO NOT ALLOW over rounding to two significant figures twice eg ALLOW the following answer for 3 marks 241 (cm3) (0.00672 was rounded to 0.0067 OR 0.0101 was rounded to 0.010) ALLOW the following answers for 2 marks 240 (cm3) (0.00672 was rounded to 0.0067 AND 0.0101 was rounded to 0.010) 252 (cm3) (0.00672 was rounded to 0.007) 161 cm3 (no multiplying by 3/2) If there is an alternative answer, check to see if there is any ECF credit possible using working below ALLOW up to correctly rounded calculator value of 0.006721044046 ALLOW up to correctly rounded calculator value ALLOW ECF for mol of KClO33/2 for 2nd mark ALLOW ECF for (mol of KClO3)3/224000<br />](https://learnah.org/wp-content/uploads/2018/08/OCR_1_QP_JUN12_answer_4-0.jpg)
