OCR A Jun 2015 Paper 1 Q1 (with explained solutions) |

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OCR A Jun 2015 Paper 1 Q1

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Answer all the questions. This question is about the elements with atomic numbers between 58 and 70. (a) Cerium, atomic number 58, is a metal. Complete the table to show the relative charge of each particle and the number of each particle found in a 140Ce2+ ion. Relative charge of each particle Number of each particle present in a 140Ce2+ ion Particle proton neutron electron [2] (b) Cerium behaves as a typical metal when it reacts with dilute sulfuric acid to form the salt cerium(III) sulfate and a second product. (i) Identify the second product.[1] (ii) Write the formula of cerium(III) sulfate and, explain what has happened to the cerium in this reaction in terms of the number of electrons transferred. FormulaExplanation[2] (iii) How has a salt been formed in this reaction?[1]OCR 2015<br />
(c) Europium, atomic number 63, reacts with oxygen at room temperature. 4Eu + 3O2 2Eu2O3 Calculate the volume of oxygen, in cm3, required to fully react with 9.12 g of europium at room temperature and pressure. (d) A compound of thulium, atomic number 69, has the following composition by mass: Volume =cm3 [2] O 30.7% S 15.4% Tm 53.9% (i) State what is meant by the term empirical formula.[1] (ii) Determine the empirical formula of the compound. Show your working. Empirical formula =[2]OCR 2015 Turn over<br />
(e) Ytterbium, atomic number 70, is the first element in the Periodic Table to have the first four shells full. (i) State the number of electrons in the fourth shell of ytterbium.[1] (ii) How many orbitals are there in the third shell of ytterbium?[1] [Total: 13]OCR 2015<br />

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F321 Mark Scheme June 2015 Question (i) 1 (a) Answer Particle Relative charge Protons Neutrons +1 Nil (or 0) Number of particles present in a 140Ce2+ ion. 58 82 Mark Guidance DO NOT ALLOW + or - without 1 DO NOT ALLOW 1 without charge ALLOW 1+ AND 1 IGNORE(ie a dash) for relative charge of a neutron (b) Electrons 56 One mark per column (cid:57) (cid:57) 1 (i) Hydrogen (cid:57) (ii) Ce2(SO4)3 (cid:57) (Cerium) loses three electrons (to form 3+ ion) (cid:57) (iii) A hydrogen ion (of an acid) has been replaced by a metal ion (cid:57) ALLOW H2 IGNORE H ALLOW alternative phrases for loses eg gives away, donates IGNORE 3 electrons transferred unless a correct direction is given eg ALLOW (Ce) transfers 3 electrons toOR (Ce) transfers 3 electrons forming Ce3+ IGNORE references to sulfate gaining electrons IGNORE references to reduction and oxidation For hydrogen ion: ALLOW H+ OR proton but DO NOT ALLOW H OR hydrogen without ion For metal ion: ALLOW cerium ion OR Ce3+ OR Ce2+ OR Ce ion But DO NOT ALLOW Ce without ion OR cerium without ion IGNORE ammonium ion<br />
Mark Scheme Mark F321 Question (c) Answer Check the answer line. If answer = 1080 cm3 award 2 marks Amount of Eu = 9.12/ 152.0 = 0.06(00) mol (cid:57) Amount of O2 = 0.0600 x 3/4 = 0.045(0) mol and Volume of O2 = 0.0450 x 24000 = 1080 cm3 (cid:57) (i) The simplest whole number ratio of atoms (of each element) present in a compound (cid:57) (ii) Check the answer line. If answer = O12S3Tm2 award 2 marks O = 30.7/ 16.0 S 15.4/32.1 Tm = 53.9 / 168.9 OR 1.9(2) mol 0.480 mol 0.319 mol (cid:57) O12S3Tm2 (cid:57) (i) 32 (cid:57) (ii) 9 (cid:57) (d) (e) Total 13 June 2015 Guidance If there is an alternative answer, 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 is allowed as 0.2. ALLOW incorrectly calculated amount of Eu x 3/4 and x 24000 correctly calculated for 2nd mark Eg 2605.7 would come from (9.12/63) x 3/4 x 24000 (note: a mass of Eu x 3/4 and x 24000 would not score M2) ALLOW smallest OR lowest for simplest ALLOW molecule for compound ALLOW 0.479 OR 0.48 for mol of S ALLOW 0.32 for mol of Tm DO NOT ALLOW Tm2(SO4)3 as empirical formula IGNORE Tm2(SO4)3 if seen in working.<br />

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