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Edexcel Jun 2011 Paper 2 Q18
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![Mark Mark Acceptable Answers Reject missing Hs/Cs (-1) H H .x .x xx H.xC.xC.xSx.H .x .x xx H H All Bonding electrons (1) Ignore any circles/bonds with electrons Two lone pairs on sulfur Dependent on eight electrons around sulfur (1) Accept all dots/crosses Fully correct methanethiol 1max Acceptable Answers Reject 104.5 (o) ( accept 91 to 105)(1) (Four pairs/two bonding pairs and two non- bonding pairs of electrons in) minimum repulsion/maximum separation/as far apart as possible (tetrahedral arrangement) Ignore the number of pairs of electrons (1) And lone/non bonding pair(s) of electrons repel more (than bond pairs/CH bonds) (1) Mark independently atoms Linear shape (-1) repel any sort of atoms Acceptable Answers Reject Mark Linear shape on its own Two pairs of electrons/two bonds (around the H atom) OR Can be shown on a diagram either with electrons or bonds (in approximate straight line) around the hydrogen (1) (Repel to) maximum separation/minimum repulsion/as far apart as possible (1) Dependent on first mark except: Allow: It has a linear shape due to maximum separation/minimum repulsion 1 max Question Number 18 (a)(i) Question Number 18 (a)(ii) Question Number 18 (b)(i)<br />
Mark Mark Mark Acceptable Answers Reject Sulfur is less electronegative (than oxygen)/not electronegative enough OR oxygen is more electronegative (than sulfur) / electronegative enough OR Hydrogen bonds can only occur between H and either N, O, or F due to the large difference in electronegativity Bigger/higher rmm/ atom/molecule alone Hydrogen not bonded to N, O, or F alone Acceptable Answers Reject Temporary asymmetrical distribution/ random arrangement of electrons/ charge (density) Ignore references to atoms/molecules OR instantaneous/temporary dipole (1) (these produce) induced dipoles OR description of induction (1) Mark independently Ignore references to atoms/molecules Any mention of permanent dipoles = 0/2 d+ and d- /+ and - unless clearly temporary Acceptable Answers Reject Ethanethiol/sulfur has more electrons (so forces are stronger) Allow sulfur has an extra shell of electrons OR ethanol/oxygen has fewer/less electrons (so forces are weaker) Allow oxygen has one fewer shell of electrons Larger charge cloud/ larger electron cloud/ more outer electrons on their own Any reference to size/radius/rmm unless with correct answer Question Number 18 (b)(ii) Question Number 18 (c)(i) Question Number 18 (c)(ii)<br />
Acceptable Answers Reject Any one from: Bubbles (of gas) /fizzing /effervescence Sodium disappears/dissolves/gets smaller White solid forms Multiple answers: number correct minus number wrong to give a maximum of 1 and a minimum of 0 Ignore: sodium floats or sinks and/or heat given out and/or hydrogen produced Acceptable Answers Na + CH3CH2SH (cid:74) CH3CH2SNa + H2 Accept multiples Ignore charges on sodium salt/state symbols even if incorrect Acceptable Answers C2H5Br + KOH (cid:74) C2H5OH + KBr/ K+ + Br Accept ionic equation C2H5Br + OH (cid:74) C2H5OH + Br Allow molecular formula of alcohol, C2H6O Acceptable Answers Typesubstitution (1) MechanismNucleophilic (1) Accept words in either order. Both words may be given on either line. N.B. This is the only way to score 2 marks! Acceptable Answers KSH /NaSH Allow KHS/NaHS or H2S Ignore state symbols Sodium rushes about (i.e. any confusion with reaction of sodium with water) Flames Steam Reject H for hydrogen CH3CH2NaS Reject Reject Reject Mark Mark Mark Mark Mark Question Number 18 (d)(i) Question Number 18 (d)(ii) Question Number 18 (e)(i) Question Number 18 (e)(ii) Question Number 18 (e)(iii)<br />
Mark Acceptable Answers Reject SO3 CO2 Attacks ozone layer CO2 causes acid rain Sulfur dioxide/SO2 (1) Causes acid rain (1) Allow effects of acid rain e.g. acid lakes/lake pollution/ crop or forest damage/limestone building damage/named metal which corrodes. [It is quite possible candidates will give details of oxidation of sulfur dioxide to sulfur trioxide and formation of sulfuric acid. Ignore any of this additional information.] Allow triggers asthma Ignore any reference to greenhouse gas/ global warming/any reference to sea pollution or sea creatures Second mark dependent on first mark except allow: If SO2 not mentioned then, SO3/H2SO4 causes acid rain for 1 mark TOTAL FOR SECTION B = 40 MARKS Question Number 18 (f)<br />](https://learnah.org/wp-content/uploads/2018/08/June_2011_MS_-_Unit_2_Edexcel_Chemistry_A-level_18-0.jpg)
