Edexcel Jan 2010 Paper 1 Q16 (with explained solutions) |

Skip to content

Edexcel Jan 2010 Paper 1 Q16

Answers available below

PMT SECTION B Answer ALL the questions. Write your answers in the spaces provided. 16 Magnesium chloride can be made by reacting solid magnesium carbonate, MgCO3, with dilute hydrochloric acid. (a) Write an equation for the reaction, including state symbols. (b) Give TWO observations you would make when the reaction is taking place. (2) (2)(c) In an experiment to make crystals of hydrated magnesium chloride, MgCl2.6H2O, magnesium carbonate was added to 25 cm3 of hydrochloric acid with concentration 2.0 mol dm3. The molar mass of magnesium carbonate is 84.3 g mol1. (i) How many moles of acid are used in the reaction? (ii) What mass of magnesium carbonate, in grams, reacts with this amount of acid? (iii) Suggest why slightly more than this mass of magnesium carbonate is used in practice. (1) (1) (1)(iv) How would you separate the magnesium chloride solution from the reaction mixture in (iii)? (1)10 *N35131A01024*<br />
PMT (2) (1) (v) The magnesium chloride solution was left to crystallise. The crystals were separated and dried carefully. A sample of 3.75g of hydrated crystals, MgCl2.6H2O, which have molar mass 203.3 g mol1, was obtained. Calculate the percentage yield of this reaction. (vi) Give ONE reason why the yield of crystals is less than 100%, even when pure compounds are used in the preparation.*N35131A01124* 11 Turn over<br />
PMT (d) Lattice energies can be measured using the Born-Haber cycle, or calculated from electrostatic theory. Lattice energies of magnesium chloride and magnesium iodide are shown below. Salt MgCl2 MgI2 Lattice energy from Born-Haber cycle using experimental data / kJ mol1 2526 2327 Lattice energy from electrostatic theory / kJ mol1 2326 1944 (i) What does this data indicate about the bonding in magnesium chloride? (1)* (ii) Explain why there is a greater difference between the experimental (Born-Haber) and theoretical lattice energies for magnesium iodide, MgI2, compared with magnesium chloride. (2)12 *N35131A01224*<br />
PMT (e) Blood plasma typically contains 20 parts per million (ppm) of magnesium, by mass. (i) Calculate the mass of magnesium, in grams, present in 100 g of plasma. (ii) Magnesium chloride can be used as a supplement in the diet to treat patients with low amounts of magnesium in the blood. Suggest ONE property which makes it more suitable for this purpose than magnesium carbonate. (1) (1)(Total for Question 16 = 16 marks) *N35131A01324* 13 Turn over<br />

Show answer

PMT Reject Mark Acceptable Answers MgCO3(s) + 2HCl(aq) MgCl2(aq) + H2O(l) + CO2(g) ALLOW MgCO3(s) + 2H+(aq) Mg2+(aq) + CO2(g) +H2O(l) All formulae and balancing (1) State symbolsmark independently; can be given even if eg MgCl2 formula incorrect or for H2CO3(aq)(1) CO3 max) ALLOW 1 missing/incorrect state symbol 2-(s) + 2H+(aq) CO2(g) +H2O(l) (1 mark Acceptable Answers Reject Carbon dioxide /gas given off Precipitate forms (no TE for MgCl2(s)) Just exothermic Reject Reject 2 / 2.12(g) Any two from Bubbles (of gas)/ fizzing/ effervescence (1) Solid disappears/ disintegrates /gets smaller /dissolves OR MgCO3 disappears (if given as solid in (i)) (1) IGNORE clear solution forms Mixture gets warmer/cooler OR temperature change occurs/ heat change occurs(1) Acceptable Answers Moles acid = ((25 x 2/ 1000)) = 0.05/0.050 / 5x10-2 Ignore units and sf Acceptable Answers Mass Mg CO3 = ((0.05 x 84.32)) = 2.1075/ 2.108 /2.11/2.1 (g) ALLOW TE from (c)(i) and (a) ALLOW Moles acid x 84.3 2 for TE(from (i) (1) (4.2(15)) if factor of 2 missing for TE from (a)) Ignore sf except 1 sf Ignore units Mark Mark Mark Section B Question Number 16 (a) Question Number 16 (b) Question Number 16 (c) (i) Question Number 16 (c) (ii)<br />
PMT Mark Mark Mark Acceptable Answers Reject To ensure all acid reacts/ all acid is used up / to ensure product is neutral/ it (HCl) is neutralised All reactants used up To ensure reaction is complete (without reference to HCl) To ensure yield is high To ensure magnesium carbonate is in excess Acceptable Answers Reject Sieve Collect MgCl2 in filter paper Use filter paper to dry crystals Evaporate Reject 70 Filter ALLOW centrifuge/ decant/ pour off / (use) filter paper Ignore comments about heating solution first to concentrate it Acceptable Answers 100% yield = (203.3 x 0.025) /5.08(25)g) (1) yield = (3.75 x 100) = 74 % (1) 5.08 OR Mol magnesium chloride = (3.75 203.3) = 0.018445/0.01845/0.0184/0.018 (1 ) yield = (100 X 0.01845 ) 0.025 = 74 % (1) Second mark can be given as TE if expected yield or number of moles is wrong. ALLOW 73.82/73.78/73.8 /73.6 /other answers rounding to 74 % from earlier approximations /72 (from 0.018 moles) Allow TE from (a) and or (c)(i) and or (c)(ii) If the ratio HCl to MgCl2 is 1:1 ans 37 % (2) If moles of HCl in (c)(i) are wrong (2) If (a) and (c)(i) are correct 37 % scores (1) If moles MgCO3 = 0.05 allow TE giving 37/ 36.9% Ignore sf except 1 sf Question Number 16 (c) (iii) Question Number 16 (c) (iv) Question Number 16 (c) (v)<br />
PMT Mark Mark Mark Acceptable Answers Reject Some stays in solution / losses on transferring from one container to another/ loss on filtering /crystals left behind/some left on filter paper etc Any one ALLOW correct answers with other comments which are not incorrect eg there may be some spillage and also . Incomplete reaction/side reaction Lost as waste products Lost to environment Lost in manipulation? Hydrolysis Weighing errors Just spillage Acceptable Answers Reject Not 100% ionic /almost completely ionic OR (partial) covalent character/ almost no covalency OR Discrepancy in BH values indicates polarisation (of ions) (1) Mark can be given if answer here refers to bond strength and the answer above is included in (ii) Magnesium chloride is covalent Magnesium chloride is partially ionic Just polarity of ions Acceptable Answers Reject QWC I- larger (than Cl-) (1) so (ion) easier to polarise /distort (1) ALLOW for 2nd mark increases covalent character / more covalent than MgCl2 / converse for MgCl2 / description of polarisation instead of the term If clearly ions, allow reference to iodine instead of iodide (iodine has a larger ion) Read in conjunction with (i). Direct comparison not needed if (i) covers bonding in chloride. Size of atoms rather than ions I2 is larger than Cl2 I2 molecules are polarised Mg2+ is polarised Iodine more electronegative than chlorine Acceptable Answers (100 x 20) = 2 x 10-3(g) 106 ALLOW 0.002(g) 1/500 (g) 2 x 10-6 kg IGNORE % as unit Reject 2 x 10-3 = 0.0002 Mark Question Number 16 (c) (vi) Question Number 16 (d)(i) Question Number 16 (d)(ii) Question Number 16 (e) (i)<br />
Acceptable Answers Reject (More) soluble (in water)/ (more) soluble in blood stream/ can be given as solution/ wont produce gas in stomach / wont react with stomach acid/ doesnt produce CO2 Converse answers for MgCO3 Or other valid answers ALLOW can be given in liquid form MgCl2 is a liquid MgCO3 is too reactive Reject PMT Mark Mark Acceptable Answers Moles N =14.42 = 1.03 14 Moles H = 3.09 Moles S= 33.06 = 1.03 (1) 32.1 ALLOW Moles S= 33.06 = 1.03 32 Moles O = 49.43 = 3.09 (1) 16 (Ratio 1:3:1:3) IGNORE sf/rounding for moles NH3SO3 any order (1) Correct answer, no working (3) If O omitted, giving NH3S (2) Acceptable Answers NH3SO3 (any order) since molar mass = empirical formula mass/ since empirical formula mass =97/ with some other justification TE from (i) N2H6S2, as empirical formula mass =49, approx half molecular mass Reject Mark Question Number 16 (e) (ii) Question Number 17 (a) (i) Question Number 17 (a) (ii)<br />

Question 16 17 18 19

About us | Need Help? | Feedback

Proudly powered by WordPress | Theme: Sydney by aThemes.