Edexcel Jan 2013 Paper 2 Q24 (with explained solutions) |

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Edexcel Jan 2013 Paper 2 Q24

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Answer ALL the questions. Write your answers in the spaces provided. SECTION C Carbon capture is the name given to some processes used to prevent carbon dioxide entering the atmosphere. Carbon capture is carried out because carbon dioxide is a greenhouse gas. Flue gases in chimneys contain carbon dioxide produced from burning fossil fuels. Various different compounds can be used to react with the carbon dioxide to capture it. Alternatively, carbon dioxide can be separated from other gases by a physical process. Many sources of natural gas contain carbon dioxide, which can be removed by freezing. Captured carbon dioxide must then be stored to prevent it entering the atmosphere. It can be injected into depleted oil and gas formations, or into porous rocks full of salt water. These are usually over 1 km below the Earths surface and have non-porous rocks above them. Eventually the carbon dioxide dissolves, forming carbonate ions and then new minerals. (a) Greenhouse gases can absorb infrared radiation. Explain why carbon dioxide absorbs infrared radiation but oxygen cannot. (2) 24(b) A solution of the compound aminoethanol, H2NCH2CH2OH, can be used to absorb carbon dioxide. 2H2NCH2CH2OH + CO2 + H2O U (H3NCH2CH2OH)2CO3 (i) Explain why aminoethanol is soluble in water. (1)16 *P41213A01624*<br />
(ii) The position of this equilibrium moves to the left on heating. This frees the captured carbon dioxide for storage. Use this information to decide whether the forward reaction is exothermic or endothermic. Explain your answer. (2)(c) The composition of a sample of natural gas and the melting temperatures of four of its components are shown below. Percentage Melting temperature / K Methane 2-methylpropane Butane Other hydrocarbons Carbon dioxide 95.2 0.8 0.9 2.4 0.7 91.1 113.7 134.7 216.5 (i) Draw a dot and cross diagram for carbon dioxide. (ii) The London forces between molecules of carbon dioxide are stronger than the London forces between molecules of methane. Suggest a reason for this. (2) (1)*P41213A01724* 17 Turn over<br />
(iii) Use your knowledge of intermolecular forces to suggest why butane has a higher melting temperature than 2-methylpropane. (2)(d) When carbon dioxide dissolves, it may eventually form minerals such as magnesium carbonate and calcium carbonate. (i) State the results of flame tests carried out on these two minerals. (2) Magnesium carbonateCalcium carbonate18 *P41213A01824*<br />
*(ii) Magnesium carbonate and calcium carbonate both undergo thermal decomposition, but they have different stability to heat. The difference in stability to heat can be compared in an experiment. Suggest how this experiment could be carried out. You should indicatehow to detect when the thermal decomposition occurshow to make the comparison fair. the measurement you would make to compare the stability to heat You may include a diagram if you wish but it is not essential. (4)*P41213A01924* 19 Turn over<br />
*(iii) State and explain which of the two carbonates is more stable to heat. (3)(Total for Question 24 = 19 marks) TOTAL FOR SECTION C = 19 MARKS TOTAL FOR PAPER = 80 MARKS 20 *P41213A02024*<br />

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Reject CO2 is a polar molecule Mark Question Number 24(a) Acceptable Answers CO2 has polar bonds / oxygen does not have polar bonds (1) Ignore O2 is a non polar molecule (As it vibrates) polarity of CO2 changes / dipole moment changes / shifts (1) Allow Oxygen has no difference in electronegativity so polarity does not change for 2 marks Question Number 24(b)(i) Hydrogen bonds can form with water Acceptable Answers Reject Mark Just it is polar Allow full description of hydrogen bonds in absence of name. Ignore incorrect naming of functional groups in aminoethanol. Question Number 24(b)(ii) Exothermic, with attempt at a reason Acceptable Answers Reject Mark Just exothermic OR reverse reaction is endothermic, with attempt at a reason (1) Reaction will go in the endothermic direction on heating / equilibrium moves to left to use up heat supplied (1) Second mark depends on the reaction being exothermic in first mark<br />
Question Number 24(c)(i) Acceptable Answers Reject Mark Electrons in double bond (1) Other electrons (1) Second mark dependent on first Only bonding electrons need be shown If inner shell electrons are included they must be correct. Electrons may be on circles, within circles or no circles may be shown. Question Number 24(c)(ii) Number of electrons (per molecule) is Acceptable Answers greater in CO2 (than methane). If numbers are given must be correct. CO2 has 22e-, methane has 10e-. Ignore CO2 has larger surface area than methane Question Number 24(c)(iii) Butane has a greater surface area / butane Acceptable Answers is less branched (1) so more contact between (neighbouring) molecules / (neighbouring) molecules pack better (1) OR Reverse argument for 2-methylpropane Reject double bonds in CO2 as the cause Mark Reject Mark Question Number 24(d)(i) Mgno colour in flame (1) Acceptable Answers Allow no flame visible Ca brick red / red / yellow-red / red-orange (1) Mark Reject Mg: white flame Bright / white light Clear flame Just orange<br />
Mark Reject First mark: Combustion Heating carbonate solution Second mark: Just measure volume of gas produced Measure time for a specified change in mass to occur Acceptable Answers Question Number 24(d)(ii) First mark: Detect thermal decomposition by Passing gas into / reacting gas with lime water OR By collecting the gas evolved (in syringe or by displacement) OR By measuring change of mass (1) Second mark: Measure time for (same volume) of lime water to go milky OR Measure volume of gas produced in a measured time OR Measure time for a specified / same volume of gas to form OR Find loss of mass after heating samples for equal time (1) The mark for measurement should only be given if it matches the suggested method of detection. Third and fourth marks: For fair comparison Any two from: Keep strength of flame constant (1) Distance of flame from containing tube constant (1) Use carbonates with similar particle size (1) Same volume of lime water (1) Heat equal moles / same amount of each carbonate (1) Judge equal milkiness of lime water using a piece of paper marked with a cross (1) The marks for fair comparison should only be given if they match the suggested method of detection. Ignore heat same mass and known mass Ignore using water bath as source of heat<br />
Ignore heat to same temperature Ignore use same heat source Ignore constant heat These points could be shown on a diagram but marks are for the principles, not the detail of drawing a sketch diagram. Question Number 24(d)(iii) CaCO3 more stable / MgCO3 less stable (1) Acceptable Answers Mg2+ is smaller than Ca2+ / magnesium ions are smaller than calcium ions / charge density of Mg2+ is greater than Ca2+ / Ca2+ has more shells (1) EITHER Mg2+ causes more distortion of carbonate ion / more weakening of C-O / more polarisation of carbonate / more polarisation of anion / has more polarising power OR More energy is given out when MgO forms as the MgO lattice is stronger than CaO /as the 2+ ions can get closer to the 2- ions on decomposition (1) Second and third marks can be scored if conclusion given in first mark is wrong Mark Reject Mg is smaller It (unspecified) is smaller MgCO3 is smaller More disruption of ion Polarisation of carbonate molecules CaO is less stable than MgO Total for Q24 = 19 marks TOTAL FOR SECTION B = 60 MARKS<br />

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