Edexcel Jan 2017 (IAL) Paper 2 Q19 (with explained solutions) |

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Edexcel Jan 2017 (IAL) Paper 2 Q19

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19 This is a question about some elements of Group 2 and their compounds. (a) Magnesium reacts slowly with cold water but rapidly when heated in steam. For each reaction, name the magnesium compound formed. Identify the other product formed in both reactions. (2) Magnesium compound formed with cold waterMagnesium compound formed with steamOther productD O N O T W R I T E I N T H I S A R E A (b) Calcium chloride can be formed in two ways by reacting calcium with different reagents. Write the equation, with state symbols, for each of these reactions. D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A Reaction 1 Reaction 2 (c) The thermal decomposition of Group 2 carbonates can be investigated using the apparatus shown. delivery tube limewater solid heat (i) State why it is necessary to remove the delivery tube from the limewater as soon as heating is stopped. (3) (1)14 *P48368A01424*<br />
A E R A S I H T N I E T I R W T O N O D (ii) Give the formula of the chemical compound in limewater that reacts with carbon dioxide. (1)(iii) Identify the chemical compound that is responsible for the cloudiness of the limewater. (1)*(iv) Magnesium carbonate took two minutes of heating to produce enough carbon dioxide to make a sample of limewater go cloudy. State and explain the trend in the time taken for decomposition as Group 2 is descended. (4) TrendA E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D Explanation(d) Explain why a saturated solution of barium hydroxide is more alkaline than a saturated solution of magnesium hydroxide. (1)*P48368A01524* 15 Turn over<br />
*(e) The colour seen in a flame test is characteristic of the metal ion involved. For example, barium ions give a green colour whilst calcium ions give a yellow-red colour. Explain, with reference to the electronic transitions involved, how these flame colours are formed and why the flame colours are different. (4)(Total for Question 19 = 17 marks) 16 *P48368A01624* D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A D O N O T W R I T E I N T H I S A R E A<br />
A E R A S I H T N I E T I R W T O N O D A E R A S I H T N I E T I R W T O N O D BLANK PAGE A E R A S I H T N I E T I R W T O N O D *P48368A01724* 17 Turn over<br />

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Acceptable Answers Reject Mark Magnesium hydroxide/Mg(OH)2 and magnesium oxide formed/MgO (1) Hydrogen gas/H2 (is also produced) (1) Standalone marks If name and formula given then both must be correct H Any other product(s) Acceptable Answers (Reaction 1) Ca(s) + Cl2(g)CaCl2(s) (Reaction 2) Ca(s) + 2HCl(aq)CaCl2(aq) + H2(g) These reactions can be given in either order One mark for each balanced equation (2 x 1) One mark for all correct state symbols in both equations. Dependent on correct species. (1) Acceptable Answers To prevent suck-back (of water into the hot boiling tube)/ description of suck back/ crack the tube Acceptable Answers Ca(OH)2 Ignore names Reject Mark Any other reactions scores 0 Reject Mark Reject Mark Reject Mark Question Number 19(a) Question Number 19(b) Question Number 19(c)(i) Question Number 19(c)(ii) Acceptable Answers Question Number 19(c)(iii) Calcium carbonate/CaCO3 If name and formula given then both must be correct<br />
Acceptable Answers Question Number 19(c)(iv) Marking point 1(trend in time taken for decomposition of Reject Mark Just stability increases Molecule Electron density Atom/anion Group 2 carbonates) take longer/ increases (1) (Explanation - As group is descended) Marking point 2 (metal ion size) (Metal) ion radius increases/has more electron shells ALLOW Atom for ion for this mark only OR Charge density of metal ion decreases (1) Marking point 3 (comparison of polarising species) Polarising power of metal ion/cation decreases (1) Marking point 4 (what is polarised) Polarisation/distortion of the electron cloud of the carbonate ion/anion decreases OR Weakening of the C-O bond in the carbonate ion decreases (1) Allow reverse argument/ As the group is ascended IGNORE Group II carbonates are less polarised as group is descended If the trend is incorrect only M2 can be awarded Acceptable Answers Magnesium hydroxide is less soluble (than barium hydroxide)/ barium hydroxide is more soluble (than magnesium hydroxide) OR Solubility of hydroxides increases as the group is descended Ignore has a higher concentration of aqueous hydroxide/OH ions Reject Mark Question Number 19(d)<br />
Question Number 19*(e) Acceptable Answers Reject Mark Just Radiation Read the whole answer before awarding marks If there is no mention of electrons, then only M3 may be awarded. If there is any reference to molecule then M1 not awarded. Marking point 1 Electrons excited/promoted (to a higher energy level/shell by thermal energy/heat from the flame) (1) Marking point 2 electron returns to its ground state/drops back (1) Marking point 3 Emitting energy/photon (in the visible region) ALLOW light/ radiation in the visible region for energy (1) Marking point 4 (The different metal ions have) different sized gaps between the energy levels (and so give different colours/wavelengths/frequency of light) (1) (TOTAL FOR QUESTION 19 = 17 MARKS)<br />
For parts a and b the observation mark is dependent on the first correct equilibrium mark. There is no TE from an incorrect equilibrium shift. Acceptable Answers Reject (The increase in chlorine gas) shifts the equilibrium position to the right (which results in the formation of more ICl3) (1) More yellow (solid formed) /brown liquid disappears/lighter brown (1) Less pale green Just turns yellow Acceptable Answers (Heating) shifts the equilibrium in the endothermic direction (which shifts the equilibrium to the left resulting in the formation of more ICl) OR shifts the equilibrium to the left because the forward reaction is exothermic (1) More brown (liquid formed) /less yellow (solid )/turns darker brown ALLOW More (pale)green gas formed (1) Acceptable Answers Chlorine is oxidised from 1 to 0 (1) Manganese is reduced from +7 to +2 ALLOW Mn is reduced from VII to II (1) If oxidation number changes of further elements are given penalise each one. Acceptable Answers Reject Just turns brown Reject To react with/absorb/remove/ excess chlorine (gas) ALLOW To prevent it entering the lab Question Number 20(a) Question Number 20(b) Question Number 20(c) Question Number 20(d) Mark Mark Mark Reject Mark (TOTAL FOR QUESTION 20 = 7 MARKS) (TOTAL FOR SECTION B = 39 MARKS)<br />

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