Structure Properties and Uses Mark Scheme 1

Transcription

1 Structure Properties and Uses Mark Scheme Level IGCSE Subject Chemistry (4402) Exam Board AQA Unit C2 Topic Structure Properties and Uses Booklet Mark Scheme Time Allowed: 54 minutes Score: / 54 Percentage: /00 Grade Boundaries: Page

2 M.(a) any one from: disposal or does not decompose (in landfill sites) or collection or sorting for recycling ignore non-biodegradable alone lack of space or more landfill sites other specified problems with waste (eg. litter or eyesore or harm to animals or destroys habitats) ignore pollution unqualified. (b) if 2 marks not awarded, award mark for one of the following: a double bond between the two carbons and no additional trailing bonds two C atoms bonded together with three single bonds to hydrogen atoms and one single bond to a chlorine atom. no additional Cl or H. 2 (c) intermolecular forces or forces between the chains allow intermolecular bonds (intermolecular forces are) weak ignore references to no cross links between chains. allow mark for weak forces between layers. which are easily overcome (by heat) or need little energy to overcome or chains / molecules can slide over one another (when heated) if weak bonds or breaking covalent bonds mentioned only the third marking point is available. (d) Monomer A carboxylic acid Page 2

3 do not allow carbolic Polymer C - ester (linkage) [8] M2.(a) because sulfur dioxide causes acid rain which kills fish / aquatic life or dissolves / damages statues / stonework or kills / stunts growth of trees if no other mark awarded then award mark for sulfur dioxide is toxic or causes breathing difficulties. (b) (i) electrons are lost (ii) (iii) Cu e Cu allow Cu 2+ Cu 2e ignore state symbols copper sulfate allow any ionic copper compound (c) (lattice of) positive ions delocalised electrons accept sea of electrons (electrostatic) attraction between the positive ions and the electrons electrons can move through the metal / structure or can flow allow electrons can carry charge through the metal / structure if wrong bonding named or described or attraction between oppositely charged ions then do not award M or M3 MAX 2 Page 3

4 (d) (copper compounds are absorbed / taken up by) plants allow crops which are burned the ash contains the copper compounds do not award M3 if the ash contains copper (metal) (e) / A r 55.6 / / / 32 moles ratio 3 3 formula Cu 3 FeS 3 award 4 marks for Cu 3FeS 3 with some correct working award 3 marks for Cu 3FeS 3 with no working if the answer is not Cu 3FeS 3 award up to 3 marks for correct steps from the table apply ecf if the student has inverted the fractions award 3 marks for an answer of CuFe 3S 4 [6] M3.(a) (i) giant lattice allow each carbon atom is joined to three others atoms in graphene are covalently bonded max. 2 marks if any reference to wrong type of bonding and covalent bonds are strong or need a lot of energy to be broken Page 4

5 allow difficult to break (ii) because graphene has delocalised electrons allow each carbon atom has one free electron which can move throughout the structure do not accept just electrons can move. (b) because there are weak forces between molecules allow no bonds between the layers so layers / molecules can slip / slide. [7] M4.(a) Sulfur dioxide causes acid rain. (b) red / orange / yellow do not accept any other colours because sulfur dioxide (when in solution) is an acid (c) (there are) weak forces (of attraction) do not accept any reference to covalent bonds breaking Page 5

6 between the molecules do not accept any other particles (these) take little energy to overcome award third mark only if first mark given (d) Marks awarded for this answer will be determined by the Quality of Communication (QC) as well as the standard of the scientific response. Examiners should also refer to the information on page 5 and apply a best-fit approach to the marking. 0 marks No relevant content Level ( 2 marks) A relevant comment is made about the data. Level 2 (3 4 marks) Relevant comparisons have been made, and an attempt made at a conclusion. Level 3 (5 6 marks) Relevant, detailed comparisons made and a justified conclusion given. examples of the points made in the response effectiveness W removes the most sulfur dioxide D removes the least sulfur dioxide material used Both W and D use calcium carbonate Calcium carbonate is obtained by quarrying which will create scars on landscape / destroy habitats D requires thermal decomposition, this requires energy D produces carbon dioxide which may cause global warming / climate change S uses sea water, this is readily available / cheap waste materials W product can be sold / is useful W makes carbon dioxide which may cause global warming / climate change Page 6

7 D waste fill landfill sites S returned to sea / may pollute sea / easy to dispose of 6 [2] M5.(a) (i) ionic (bonding) (ii) ions cannot move in solid or are in fixed positions do not accept electrons / atoms / molecules ignore particles must mention ions but can move in solution (b) silver chloride formed which is insoluble (c) (i) aluminium calcium accept other metal ions that also give white precipitates (such as lead and zinc) (ii) add excess sodium hydroxide solution the second mark of each pair is dependent on the first mark being awarded. Page 7

8 precipitate remains carry out a flame test not red / orange accept any colour that is not orange / red give full credit for answers that correctly eliminate other cations in (c)(i) that would give white precipitates with a few drops of NaOH [] Page 8