Edexcel Jun 2016 Paper 1 Q21 (with explained solutions) |

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Edexcel Jun 2016 Paper 1 Q21

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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 21 This question is about ethane and ethene. (a) Ethane reacts with chlorine by a free radical mechanism. (i) Explain what is meant by the term free radical. (1)(ii) Complete the equation for the formation of free radicals from one molecule of chlorine. Use appropriate curly arrows to show electron movements. Cl Cl (cid:111) (iii) Write an equation for the reaction between ethane and a chlorine free radical, and name the type of step in the mechanism where this occurs. Curly arrows are not required. (1) (2) Type of step(iv) Give an equation for a termination step in this mechanism in which an organic compound other than chloroethane is formed. (1) A E R A S I H T N I E T I R W T O N O D *P46656A02124* 21 Turn over<br />
(b) Ethene contains a carbon-carbon double bond. (i) Complete the diagram below showing the (cid:305) and (cid:652) bonds in the carbon-carbon double bond in ethene. C C *(ii) Describe and explain what happens to the (cid:305) and (cid:652) bonds in ethene in an addition reaction. (2) (3)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 (iii) One test for a carbon-carbon double bond is the reaction with acidified potassium manganate(VII), KMnO4. Give the colour change if this reaction was carried out with ethene. Draw the displayed formula of the product. FromtoDisplayed formula N T H I S A R E A (2) D O N O T W R I T E I (iv) Describe another test for a carbon-carbon double bond and give the colour change for the positive result. (2) TestFromto22 *P46656A02224* N T H I S A R E A<br />
(v) Ethene reacts with hydrogen bromide. Write the mechanism for this reaction, showing any relevant dipoles. Mechanism: (c) But-1-ene is an alkene with properties similar to ethene. Write an equation, using skeletal formulae for the organic compounds, showing the conversion of but-1-ene to butane. State the essential condition needed. (4) (2) Condition(Total for Question 21 = 20 marks) TOTAL FOR SECTION B = 60 MARKS TOTAL FOR PAPER = 80 MARKS 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 A E R A S I H T N I E T I R W T O N O D *P46656A02324* 23<br />

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Acceptable Answers Question Number 21(a)(i) Species/ atom/ molecule/ particle with an unpaired electron ALLOW An element with an unpaired electron IGNORE Reference to neutral species /lack of charge Mark (1) Reject Just with a single electron A lone electron Charged particle with an unpaired electron Acceptable Answers Question Number 21(a)(ii) Half arrows going from bond to Cl or just beyond and product 2Cl / Cl + Cl Reject Cl withoutMark (1) Reject C2H5 Mark (2) Question Number 21a(iii) Acceptable Answers C2H6 + ClC2H5 + HCl ALLOW Structural formulae e.g. CH3CH3 OR displayed IGNORE Production of C2H5Cl from C2H5 if first step is correct (1) Propagation (1) The second mark is independent of the first<br />
Mark (1) Acceptable Answers Reject Methyl or propyl radicals C2H5 + C2H5C4H10 ALLOW Structural formulae e.g. CH3CH2 / CH3CH2 OR displayed IGNORE Cl + ClCl2 Acceptable Answers Reject Mark (2)bond between C atoms shown as 2 overlapping orbitals/ one electron cloud/ single bond (1)bond above and belowbond shown as two electron clouds/ overlapping p orbitals/ p orbitals linked by a line / a curved line above and below single bond (1) Both bonds must be labelled for 2 marks. Question Number 21a(iv) Question Number 21b(i)<br />
Acceptable Answers Question Number *21b(ii) MP1bond remains ALLOW The product containsbonds only (1) MP2bonds break because they are weaker (thanbonds) ALLOWbonds break becausebonds are stronger (1) MP3 Breaking thebond results in carbocation intermediate / positively charged carbon forming ORorbital overlap is lateral/ sideways /between parallel orbitals (makingbonds break/ weak) OR Thebonds are much stronger (than thebond) because of more effective (orbital) overlap (1) Acceptable Answers Question Number 21(b)(iii) From: Purple/ pink (solution) To: colourless (1) (1) Any orientation Dont penalise undisplayed OH Dont penalise bonds going to middle of undisplayed OH Reject Mark (3) Mark (2) Reject To brown Molecular/ structural/ skeletal formulae C bonded to H of OH<br />
Reject Mark (2) Acceptable Answers Question Number 21(b)(iv) Second mark depends on use of bromine/ solution of bromine for test. EITHER Test: add bromine water / Br2(aq) ALLOW Add bromine in organic solvent/ bromine dissolved in hexane/ bromine in 1,1,1-trichloroethane (1) From: brown/ red-brown/orange/ yellow To: colourless (1) OR Add bromine / Br2 (1) From: brown/ red-brown To: colourless (1)<br />
Acceptable Answers Reject Mark (4) Half arrows Mark (2) Dipole on HBr (1) Curly arrow from C=C double bond to H+ of HBr and curly arrow from H-Br bond to Br (1) Correct intermediate with + charge (1) Curly arrow from Br to C+ and formula of product ALLOW Curly arrow from anywhere on Br, including thesign or lone pair (which is optional) (1) Acceptable Answers Reject + H2(1) Suitable catalyst nickel/ platinum/ palladium (1) Ignore references to temperature, pressure, uv light Use of H, H+ Zeolite catalyst (Total for Question 21 = 20 marks) TOTAL FOR PAPER = 80 MARKS Question Number 21(b)(v) Question Number 21(c)<br />

Question 18 19 20 21

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