Edexcel Jan 2013 Paper 1 Q17 (with explained solutions) |

Skip to content

Edexcel Jan 2013 Paper 1 Q17

Answers available below

SECTION B Answer ALL the questions. Write your answers in the spaces provided. 17 This question is about the preparation of the alum, potassium aluminium sulfate, KAl(SO4)2(cid:116)12H2O. It is a double salt consisting of potassium ions, aluminium ions and sulfate ions, and water of crystallization. (a) The first step of the preparation involves adding an excess of aluminium foil to 10 cm3 of 2 mol dm3 potassium hydroxide to form potassium aluminate. The equation for this reaction is 2Al(s) + 2KOH(aq) + 2H2O(l) o 2KAlO2(aq) + 3H2(g) (i) Write a balanced ionic equation for this reaction. (1) (1) (1) (1) (ii) Calculate the number of moles of potassium hydroxide used. (iii) Hence state the number of moles of aluminium that react with the potassium hydroxide. (iv) Use your answer to (iii) to calculate the mass of aluminium that reacts with the potassium hydroxide. Use the Periodic Table as a source of data. 10 *P41212A01024*<br />
(v) Calculate the total mass of aluminium added to the potassium hydroxide if a 10% excess of aluminium is required. (vi) Identify two hazards in this first step of the preparation. (1) (2) Hazard 1Hazard 2(b) The second step of the reaction is the addition of a slight excess of 1 mol dm3 sulfuric acid. (i) Balance the following equation for the reaction KAlO2(aq) + H2SO4(aq) o KAl(SO4)2(aq) + H2O(l) (ii) Calculate the volume of the 1 mol dm3 sulfuric acid that reacts with the potassium aluminate. (iii) State how you would show that the acid had been added in excess. (1) (1) (2)*P41212A01124* 11 Turn over<br />
*(iv) State and explain the steps necessary to obtain pure, dry crystals from the mixture. (4)(v) Suggest the colour of the crystals. (1)(vi) Suggest the formula of another metal ion which could form an alum, in combination with potassium and sulfate ions. (1)(Total for Question 17 = 17 marks) 12 *P41212A01224*<br />

Show answer

PMT Acceptable Answers 2Al(s) + 2OH(aq) +2H2O(l) (cid:74) 2AlO2 (aq) + 3H2(g) Acceptable Answers 2 x 10 = 0.02 / 2 x 102 1000 Ignore trailing zeroes Acceptable Answers 0.02 / 2 x 102 Accept TE answer to (ii) Acceptable Answers 0.02 x 27.0 = 0.54 / 5.4 x 101 (g) TE answer to (iii) OR (ii) x 27.0 Ignore sf except 1 Acceptable Answers (1.1 x 0.54) = 0.59(4) / 5.9(4) x 101(g) TE answer to (iv) x 1.1 Ignore sf except 1 Only penalise sf once Reject Mark 202 2-(aq) Reject Mark Reject Mark Reject Mark Other unit Reject Mark Section B Question Number 17 (a) (i) Question Number 17 (a)(ii) Question Number 17 (a)(iii) Question Number 17 (a)(iv) Question Number 17 (a)(v)<br />
PMT Mark Reject Toxic, carcinogenic, alone or in combination with correct answer Burns alone Additional chemicals Reject Reject Mark Mark Question Number 17 (a)(vi) Question Number 17 (b)(i) Question Number 17 (b)(ii) Acceptable Answers Potassium hydroxide / KOH (solution) is corrosive / burns / caustic OR KOH damages / harms / is harmful to / dissolves / reacts with skin / eye(s) (1) OR KOH in eye(s) (1) Ignore Harmful, irritant, highly reactive alone Hydrogen / H2 is flammable / explodes / explosive (1) Allow mention of both potassium hydroxide and hydrogen alone scores (1) Allow Al foil can cut your skin (1) Correct answer with additional incorrect chemistry e.g. KOH is oxidising so corrosive scores (0) Acceptable Answers KAlO2(aq) + 2H2SO4(aq) (cid:74) KAl(SO4)2(aq) + 2H2O(l) Allow multiples Acceptable Answers 2 x 1000 x 0.02 =40 (cm3) 1 Allow 0.04(0) dm3 TE answer to (a)(ii) x 2000 and TE from (b)(i)<br />
PMT Mark Acceptable Answers Reject Litmus (paper / solution) (1) Red / pink (in acid) (1) OR any other named acid-base indicator including universal indicator (1) with a correct acidic colour (1) NB phenolphthalein must be spelt correctly to score (1) and no mark for colour Notice that other indicators only require recognisable spellings Red litmus turns blue scores for the indicator (1) OR pH meter / universal indicator (1) with value < 7 (1) NB measure pH alone (0) pH < 7 (1) OR add a (metal) carbonate / suitable metal eg Mg (1) bubbles / fizzing (1) Calculation of amounts / moles of both reactants (1 maximum) Question Number 17 (b)(iii)<br />
PMT Mark Acceptable Answers Each point must be made in full The second and final scoring points, which are asterisked, can only be gained through these statements. Two further marks can be scored for any two of the other four points. 1 Filter (to remove any aluminium / impurities) (1) NB This mark can only be awarded if it is the first action and the mixture is subsequently heated. 2 *Boil / heat / evaporate to reduce the volume of water (1) NB boil / heat to remove water only gets the mark if it is clear, subsequently, that some solution is left 3 Cool / set aside / leave to allow crystals to form (1) 4 Filter OR pick out / remove / take out crystals (to separate) (1) 5 Wash with a little/cold water (1) 6 *Place between filter papers / dab with paper towel / use dessicator (to dry) (1) Reject Leave in the sun If boiled to dry stop marking here Heat in oven Acceptable Answers Question Number 17 (b)(v) White / colourless Ignore clear / transparent / cloudy / opaque e.g. accept clear and colourless Reject Any other colours with or without white Mark Question Number 17 (b)(iv)<br />
PMT Question Number 17 (b)(vi) Acceptable Answers Cr3+/ Fe3+/ Sc3+ / Ga3+ Accept any feasible triply positive metal ion Allow B3+ Allow any name or symbol for a Group 3 element Allow named existing transition metal ions with (III) after the name (if they exist) Fully correct formula for an alum or intermediate starting entity Eg KGa(SO4)2 / KGaO2 Mark Reject Al3+ and anything else Group 3 element with incorrect charge<br />

Question 17 18 19 20

About us | Need Help? | Feedback

Proudly powered by WordPress | Theme: Sydney by aThemes.