Edexcel Jun 2015 Paper 2 Q19 (with explained solutions) |

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Edexcel Jun 2015 Paper 2 Q19

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19 Two white powders, A and B, known to be Group 2 carbonates, are investigated. (a) (i) The presence of the carbonate ion is usually confirmed using a simple test carried out in two stages at room temperature. Describe this test and its results. (2) TestResults(ii) Using barium carbonate as your example, write the equation for each of the stages of the carbonate test. Include state symbols in both equations. (3) First equation (test) Second equation (result) 14 *P44881A01424*<br />
(b) When a flame test is carried out on the two powders, A gives no colour and B gives a yellow-red flame. (i) Describe how a flame test is carried out. (3)(ii) Give the formulae of the metal ions in A and B. AB*(iii) Explain the origin of the flame colour. (2) (3)(iv) Suggest why compound A produces no flame colour. (1)*P44881A01524* 15 Turn over<br />
*(c) When Group 2 metal carbonates are heated strongly, they decompose forming the metal oxide and carbon dioxide. Explain why the thermal stability of the metal carbonates increases as the group is descended. (3)(Total for Question 19 = 17 marks) 16 *P44881A01624*<br />

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Question Number 19(a)(ii) ALLOW Acceptable Answers Reject Mark Mark Reject Just acid OR heating the carbonate Acceptable Answers Question Number 19(a)(i) Add hydrochloric acid / HCl(aq) / nitric acid / HNO3(aq) ALLOW Just acid only if a suitable acid is given in equation one Sulfuric acid / H2SO4((aq)) or HCl (1) IGNORE conc Gas / carbon dioxide / CO2 evolved turns lime water milky / cloudy / produces a white precipitate (1) MP2 is a stand alone mark but there must be some indication that a gas is being tested 2(s) + 2H+(aq)H2O(l) + CO2(g) H2CO3(aq) for H2O(l) + CO2(g) BaCO3(s) + 2HCl(aq)BaCl2(aq) + H2O(l) + CO2(g) OR BaCO3(s) + 2HNO3(aq)Ba(NO3)2(aq) + H2O(l) + CO2(g) OR CO3 ALLOW BaCO3(s) + H2SO4(aq)BaSO4(s/aq) + H2O(l) + CO2(g) OR BaCO3(s)BaO(s) + CO2(g) (1) Ca(OH)2(aq) + CO2(g)CaCO3(s) + H2O(l) (1) All state symbols in both equations correct (1) ALLOW State symbols mark if first equation not balanced but ALL species are correct. No TE on other equations<br />
Question Number 19(b)(i) MP1 and MP2 Acceptable Answers Reject Mark Nickel / chrome / chromium spatula Other acids just water Dip (clean) nichrome / platinum wire ALLOW loop / rod for wire OR Silica rod (1) in hydrochloric acid / HCl(aq) ALLOW any mention of HCl(aq) e.g. cleaning or mixing solid and acid HCl for HCl(aq) (1) ALLOW (for MP1 and MP2) (Wooden) splint (1) Soaked in distilled / deionised water (1) MP3 then dipped in solid and placed in (hot / roaring / blue-cone) (Bunsen) flame ALLOW On / over / under / above for in (1) IGNORE inoculating / flame-test (wire) Reject Mark Acceptable Answers Question Number 19(b)(ii) A = Mg2+ (1) B = Ca2+ (1) Penalise omission of 2+ only once Correct ions with correct charge but the wrong way round scores 1 mark Correct ions with incorrect / no charge scores 1 IGNORE Names / compounds<br />
Acceptable Answers Question Number 19(b)*(iii) Read the whole answer before Question Number 19(b)(iv) Emitted radiation is not in the visible Acceptable Answers region (of the spectrum) ALLOW Emitted radiation is in IR / UV awarding marks. If no mention of electrons only MP3 may be awarded. Electrons promoted to higher energy level (by thermal energy / heat from (Bunsen) flame) (1) (Promoted) electrons fall / drop / relax to lower energy level / orbital / shell / subshell OR Electrons return to ground state (1) Emitting radiation / light / photons (in the visible region) (1) IGNORE Colour Mark Reject Just electrons promoted/ excited Just energy lost Just energy given out Reject Mark<br />
Acceptable Answers Reject Mark Just metal Just ion Just ion or bond As group is descended First mark (metal ion size) (Metal) ion radius increases / has more (electron) shells (but charge remains the same) OR Charge density of metal ion decreases ALLOW (Metal) atomic radius increases / has more (electron) shells (1) Second mark (polarizing species) Polarizing (ALLOW distorting) power of cation / metal ion decreases (1) Third mark (polarized species) Polarization / distortion of (electron cloud of) carbonate ion /anion decreases ALLOW CO / CO for carbonate ion (1) (so carbonate more stable to heat) ALLOW reverse argument for ascent of the group. Total for Question 19 = 17 marks Question Number 19(c)<br />

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