Skip to content
Edexcel Jan 2014 (IAL) Paper 4 Q19
Answers available below
Show answer
Question
16
17
18
19
![SECTION C Answer ALL the questions. Write your answers in the spaces provided. 19 This question is about sucrose, the chemical commonly known as sugar. Some thermochemical data for sucrose and oxygen are given in the table below. Standard entropy of sucrose, S (cid:57) [C12H22O11(s)] Standard enthalpy change of combustion of sucrose, (cid:507)H(cid:57) c Standard entropy of oxygen, S (cid:57) [O2(g)] +392.4 J mol1 K1 5639.7 kJ mol1 +102.5 J mol1 K1 The equation for the complete combustion of sucrose, C12H22O11, is C12H22O11(s) + 12O2(g) (cid:111) 12CO2(g) + 11H2O(l) (a) (i) Calculate the standard entropy change of the system, (cid:507)S (cid:57) system, for this combustion, using the data given in the table and your Data Booklet. Include a sign and units in your answer. (ii) Calculate the standard entropy change of the surroundings, (cid:507)S (cid:57) this combustion at 298 K. Include a sign and units in your answer. surroundings, for (3) (2) *P44451A02124* 21 Turn over<br />
(iii) Calculate the total standard entropy change for the combustion, (cid:507)S(cid:57) total, at 298 K. State the significance of your answer. (2)(iv) State and explain the effect, if any, of increasing the temperature on (cid:507)S (cid:57) surroundings, (cid:507)S (cid:57) total and the extent of the reaction. (3)(v) Icing sugar can be hazardous when it is being finely powdered in a factory. Explain why sucrose is stable at room temperature, in spite of your answer to part (iii), but its manufacture is hazardous. (2)(vi) Suggest two risks associated with high levels of sucrose in the diet. (2)22 *P44451A02224*<br />
(b) Sucrose can be hydrolysed by warming with dilute hydrochloric acid to form glucose and fructose. In aqueous solution, a structure of glucose is CHO H C OH HO C H H C OH H C OH CH2OH (i) Circle or mark with an asterisk (*) all the chiral centres on the structure of glucose. (ii) State the physical property associated with molecules which have chiral centres. (2) (1)(iii) State what change you would expect to see when glucose is boiled with Benedicts or Fehlings solutions. Explain the chemistry involved in this reaction. (3)(Total for Question 19 = 20 marks) TOTAL FOR SECTION C = 20 MARKS TOTAL FOR PAPER = 90 MARKS *P44451A02324* 23<br />](https://learnah.org/wp-content/uploads/2018/08/l_smalljpgJanuary_2014_IAL_QP_-_Unit_4_Edexcel_Chemistry_A-level_19-0.jpg)
![Acceptable Answers Mark Penalise lack of + sign once only in (a)(i) or (ii) in each final answer IGNORE sf in (a)(i), (ii), and (iii) in each final answer, except 1 sf FIRST, CHECK THE FINAL ANSWER +479.7 J mol-1 K-1 scores 3 marks 479.7 J mol-1 K-1 scores 2 marks (+ sign missing) +479.7/ 479.7 scores 2 marks (units and/or + missing) +1709.7 J mol-1 K-1 scores 2 marksmultiple of 12 used for oxygen 1709.7 J mol-1 K-1/ +1709.7/ 1709.7 score 1 markmultiple of 12 used for oxygen and positive sign and/or units If these answers are not given, award marks as follows: First mark correct data for CO2 (213.6) and H2O (69.9) (1) Second mark correct multiples (12, 11, 1 and 24) and Hesss Law applied So system = 12 x 213.6 + 11 x 69.9 (392.4 + 24 x 102.5) ALLOW ecf from incorrect data for CO2 and/or H2O (1) Third mark correct answer with sign and units = +479.7 J mol-1 K-1 ALLOW ecf from incorrect data for CO2 and/or H2O and incorrect multiples (1) Acceptable Answers Reject Mark surroundings = Ho If answer is +18925.2 J mol-1 K-1/ +18.9252 kJ mol-1 K-1, then award 2 marks If not, So T (1) = - (-5639.7) x 1000 298 = + 18925.2 J mol-1 K-1 / +18.9252 kJ mol-1 K-1 (1) +18925.1 J mol-1 K-1/ +18.9251 kJ mol-1 K-1 Question Number 19(a)(i) Question Number 19(a)(ii)<br />
Acceptable Answers Mark total = So surroundings +So system = 18925.2 + 479.7) First mark (So = (+)19404.9 (J mol-1 K-1)/ (+)19.4049 (kJ mol-1 K-1) if units given they must be correct ALLOW (+)19500 (J mol-1 K-1)/ (+)19.5 (kJ mol-1 K-1) (from 19.0 + 0.480) ALLOW ecf on adding answers to (a)(i) and (a)(ii) in the same units (1) Note If answer to (a)(i) was +1709.7, So Second mark (So feasible/ goes to completion ALLOW thermodynamically unstable If their sign for So spontaneous/ not feasible/ does not go to completion (1) total is positive so) reaction is (thermodynamically) spontaneous/ total = +20634.9 (J mol-1 K-1) / +20.6349 (kJ mol-1 K-1) total is negative, then ALLOW reaction is not Question Number 19(a)(iii)<br />
total = So total less positive/ decreases system so increase in T makes) surroundings = Ho/T so increase in T makes) surroundings less positive/ decreases IGNORE comments on So First mark (So So ALLOW more negative (1) Second mark (So surroundings + So So ALLOW more negative NOTE no ecf on So Third mark (because So there is an insignificant effect on the extent of the reaction ALLOW So spontaneous ALLOW ecf on So total is still positive so reaction still goes to completion/is surroundings increases (1) total is so large and positive to start with) more exothermic Acceptable Answers Reject Mark system total increases (1) Acceptable Answers Reject Mark First mark (stable because) high activation energy/ Ea (for combustion of sucrose) ALLOW sucrose is kinetically stable/ inert (1) Second mark (hazardous because small particles/ powder have/ has) larger surface area and react faster (1) IGNORE any reference to temperature If answers are not linked to stability and hazardous, still award both marks even if the points are written in the wrong order Question Number 19(a)(iv) Question Number 19(a)(v)<br />
Acceptable Answers Reject Mark Any two of: obesity/ weight gain/ stored as fat/ get fat (1) tooth decay/ cavities/ toothache (1) diabetes/ glycosuria (1) heart/ cardiovascular condition/ disease/ attack (1) strokes (1) damage to the immune system (1) high insulin levels (1) high blood pressure (1) kidney damage (1) liver disease (1) headaches/ migraines (1) arthritis (1) high cholesterol (1) IGNORE risk of cancer/ high blood sugar/ stomach ulcers Acceptable Answers Reject Mark circles or asterisks on carbons 2-5 all four correct (2) 3 or 2 correct (1) 1 or 0 correct (0) ALLOW 5 carbons circled (1) all 6 carbons circled (0) Acceptable Answers Reject Mark rotate the plane of (plane-) polarized light ALLOW rotate plane-polarized light IGNORE optically active/ optical activity/ non- superimposable just rotate light Question Number 19(a)(vi) Question Number 19(b)(i) Question Number 19(b)(ii)<br />
First markcolour change from a blue (solution) to a red/ orange/ brown/ yellow precipitate ALLOW solid or (s) for precipitate which could be shown in formula or equation (1) Second markfunctional group (glucose/it is) an aldehyde / (has) a CHO group (1) Third markoxidation/reduction copper(II)/Cu2+ is reduced (to copper(I)/Cu+ oxide by the aldehyde group) /Cu2+ + e(-)Cu+ OR the aldehyde/ glucose is oxidized (to the carboxylate/carboxylic acid)/ RCHO + [O]RCOOH OR Benedicts and Fehlings (solutions) are oxidizing agents ALLOW equation showing oxidation of aldehyde and reduction of Cu2+ even if not balanced (1) incorrect observation for one of the reagents for first mark only, eg. silver mirror formed Total for Question 19 = 20 marks Question Number 19(b)(iii) Acceptable Answers Reject Mark<br />](https://learnah.org/wp-content/uploads/2018/08/January_2014_IAL_MS_-_Unit_4_Edexcel_Chemistry_A-level_19-0.jpg)
