OCR A Jun 2013 Paper 1 Q4 (with explained solutions) |

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OCR A Jun 2013 Paper 1 Q4

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4 Group 2 elements react with halogens. 10 (a) Describe and explain the trend in reactivity of Group 2 elements with chlorine as the group is descended. In your answer you should use appropriate technical terms, spelled correctly.[5]OCR 2013<br />
(b) A student was provided with an aqueous solution of calcium iodide. 11 The student carried out a chemical test to show that the solution contained iodide ions. In this test, a precipitation reaction took place. (i) State the reagent that the student would need to add to the solution of calcium iodide.[1] (ii) What observation would show that the solution contained iodide ions?[1] (iii) Write an ionic equation, including state symbols, for the reaction that took place.[1] (iv) The student is provided with an aqueous solution of calcium bromide that is contaminated with calcium iodide. The student carries out the same chemical test but this time needs to add a second reagent to show that iodide ions are present. State the second reagent that the student would need to add.[1] [Total: 9]OCR 2013 Turn over<br />

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F321 Question 4 (a) Mark Scheme June 2013 Answer Reactivity increases (down the group) (cid:57) Increasing size mark Atomic radius increases OR There are more shells (cid:57) Increased shielding mark There is more shielding (cid:57) Nuclear attraction (to electron) mark Nuclear attraction (to electron) decreases OR (outermost) electrons experience less attraction (to nucleus) OR Increased nuclear charge is outweighed by increased shielding/distance (cid:57) Ease of electron loss mark Easier to remove (outer) electron(s) OR Ionisation energy decreases (cid:57) Quality of written communication electron(s) OR ionisation OR ionization OR oxidise OR oxidize spelled correctly at least once for last marking point 12 Marks Guidance FULL ANNOTATIONS WITH TICKS, CROSSES, CON, etc MUST BE USED Down the group is not required ORA throughout ALLOW alternative phrases for reactivity increases ALLOW there are more energy levels ALLOW electrons are in higher energy levels ALLOW electrons are further from the nucleus IGNORE there are more orbitals OR more sub-shells ALLOW different shell OR new shell There must be clear comparison ie more shielding OR increased shielding ALLOW there is more electron repulsion from inner shells DO NOT ALLOW responses which have no comparative eg there is shielding ALLOW there is less nuclear pull OR electrons less tightly held IGNORE there is less effective nuclear charge IGNORE nuclear charge for nuclear attraction If question is answered in terms of only Group 7, then ONLY marks 2, 3 and 4 can be awarded ALLOW easier to oxidise<br />
F321 Question 4 (b) Answer (i) AgNO3(aq) OR silver nitrate OR AgNO3 (cid:57) (ii) Yellow AND precipitate (cid:57) (iii) Ag+ (aq) + I(aq) (cid:206) AgI(s) (cid:57) (iv) concentrated (aqueous) NH3 (cid:57) Mark Scheme Marks Total June 2013 ALLOW Ag+(aq) Guidance ALLOW shades of yellow but not creamy yellow ALLOW ppt or solid for precipitate ALLOW correct multiples 13<br />

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