OCR A Jun 2014 Paper 1 Q5 (with explained solutions) |

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OCR A Jun 2014 Paper 1 Q5

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PMT The Periodic Table is arranged in periods and groups. (a) Elements in the Periodic Table show a periodic trend in atomic radius. State and explain the trend in atomic radius from Li to F. In your answer you should use appropriate technical terms, spelled correctly. trendexplanation[3] (b) (i) Complete the electron configuration of a bromide ion. 1s2[1] (ii) A student adds a small volume of aqueous silver nitrate to an aqueous solution of bromide ions in a test-tube. The student then adds a similar volume of dilute aqueous ammonia to the same test-tube. Describe what the student would see in the test-tube after the addition of aqueous ammonia.[1] (iii) Write an ionic equation for any precipitation reaction which occurs in the students tests. Include state symbols.[1]OCR 2014<br />
PMT (c) The Group 7 element chlorine reacts with sodium hydroxide, NaOH, under different conditions to give different products. (i) Chlorine reacts with aqueous sodium hydroxide to form bleach. Write the equation and state the conditions for this reaction. equationconditions[2] (ii) Under different conditions, chlorine reacts differently with aqueous sodium hydroxide. A disproportionation reaction takes place as shown below. 3Cl2(g) + 6NaOH(aq) 5NaCl (aq) + NaCl O3(aq) + 3H2O(l) State what is meant by disproportionation and show that disproportionation has taken place in this reaction. Use oxidation numbers in your answer.[3] [Total: 11]OCR 2014 Turn over<br />

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F321 Question 5 (a) Mark Scheme June 2014 Answer M1 Trend AND nuclear charge mark (from Li to F) atomic radius decreases AND nuclear charge increases or number of protons increases(cid:57) M2 same shell/shielding mark (outer) electrons are in same shell OR (outer) electrons experience similar or same shielding (cid:57) OR same number of shells M3 nuclear attraction mark Greater nuclear attraction on (outer) electrons or shells OR (Outer) electrons or shells are attracted more strongly to the nucleus (cid:57) Mark Guidance ALLOW ORA throughout if it is clear that the Period is being crossed right to left ALLOW proton number increases IGNORE atomic number increases IGNORE nucleus gets bigger IGNORE effective nuclear charge increases DO NOT ALLOW charge increases without reference to nuclear IGNORE there is shielding DO NOT ALLOW sub-shells OR orbitals DO NOT ALLOW electrons are at a similar distance This will also contradict M1 ALLOW there is no change in shielding IGNORE shielding has no effect DO NOT ALLOW there is no shielding Quality of written communication nucleus OR nuclear spelled correctly once and used in context for third marking point ALLOW pull for attraction IGNORE for M3, electrons are pulled closer to nucleus as this is a re-statement of the trend mark. DO NOT ALLOW greater nuclear charge for greater nuclear attraction for M3<br />
F321 Mark Scheme June 2014 Question 5 (b) (i) Answer (1s2) 2s2 2p6 3s2 3p6 3d10 4s2 4p6 (cid:57) (b) (b) (c) (ii) Cream AND precipitate (cid:57) (iii) Ag+(aq) + Br(aq) (cid:198) AgBr(s) (cid:57) (i) Equation 2NaOH + Cl2 (cid:198) NaCl + NaClO + H2O (cid:57) Conditions cold AND dilute (sodium hydroxide) (cid:57) Mark Guidance ALLOW4s2 3d104p6 ALLOW subscripts AND 3D IGNORE 1s2 seen twice ALLOW solid OR ppt for precipitate IGNORE does not dissolve OR partially dissolves Equation AND state symbols required ALLOW correct multiples IGNORE state symbols ALLOW room temperature OR20OC for cold 10<br />
F321 Mark Scheme June 2014 Mark Guidance ALLOW an element OR a species for the same element Assume it means disproportionation M1 can be awarded for chlorine is oxidised and reduced and this is disproportionation ALLOW oxidation numbers written above the equation if not seen in the text but IGNORE oxidation numbers written above the equation if seen in the text ALLOW 1 AND 5 AND 5+ DO NOT ALLOW chloride in place of chlorine except for NaCl DO NOT ALLOW Cl in NaCl AND Cl5+ in NaClO3 (ie do not allow ionic charges for oxidation numbers) ALLOW Cl OR Cl2 for chlorine DO NOT ALLOW M2 if incorrect oxidation numbers of other elements are seen in the text eg H = +2 ALLOW ECF for third marks if ONE incorrect oxidation number is assigned but directional changes are correct eg Cl = 0 and -1 and +3 instead 0 and -1 and +5 DO NOT ALLOW ECF if two oxidation numbers are incorrectly assigned IGNORE references to electron loss/gain If oxidation numbers are correct ALLOW third mark for: chlorine is oxidised to form NaClO3 AND chlorine is reduced to form NaCl Question (5) (c) Answer (ii) Definition of disproportionation mark M1 (Disproportionation) is the (simultaneous) oxidation and reduction of the same element (in the same redox reaction) (cid:57) M2 Assigning of oxidation numbers Cl in Cl2 is 0 AND Cl in NaCl is -1 AND Cl in NaClO3 is +5 (cid:57) M3 Chlorine has been oxidised from 0 to +5 AND Chlorine has been reduced from 0 to 1 (cid:57) Chlorine has been oxidised from 0 in Cl2 to +5 in NaClO3 and chlorine has been reduced from 0 in Cl2 to -1 in NaCl would secure M2 and M3 3Cl2 + 6NaOH (cid:198) 5NaCl + NaClO3 + 3H2O 0 -1 +5 reduction oxidation This diagram, along with a correct definition, would secure all three marks. Total 11 11<br />

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