Hong Kong Examinations and Assessment Authority All Rights Reserved 2012 PP-DSE-CHEM 1–1
。旨之巧技用運與力能解理重着試考違有亦 ，難解及對應懂學，習學善改生學助無既，度態習學種這。吞生剝 活，記死背硬，案答準標為視考參卷評將應不生學。用之考參生學 和師教供，寫編而卷習練科本為專局核評及試考港香乃考參卷評本 This marking scheme has been prepared by the Hong Kong Examinations and Assessment Authority for teachers’ and students’ reference. This marking scheme should NOT be regarded as a set of model answers. Our examinations emphasise the testing of understanding, the practical application of knowledge and the use of processing skills. Hence the use of model answers, or anything else which encourages rote memorisation, will not help students to improve their learning nor develop their abilities in addressing and solving problems.
Part I Question No. 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. Part II Question No. 25. 26. 27. 28. 29. 30. 31. 32. 33. 34. 35. 36. Key A D A B C A D B D C B C Key B D A D C B B C B B B A A C D A D A C C B A D D
SECTION B General Notes for Teachers on Marking
The marking scheme has been updated, with revisions made after the scrutiny of actual samples of student performance in the practice papers. Teachers are strongly advised to conduct their own internal standardisation procedures before applying the marking schemes. After standardisation, teachers should adhere to the marking scheme to ensure a uniform standard of marking within the school.
The marking scheme may not exhaust all possible answers for each question. Teachers should exercise their professional discretion and judgment in accepting alternative answers that are not in the marking scheme but are correct and well reasoned.
The following symbols are used:
A single slash indicates an acceptable alternative within an answer. Step-mark (for questions involving calculations) Correct spelling required
In questions asking for a specified number of reasons or examples etc. and a student gives more than the required number, the extra answers should not be marked. For instance, in a question asking students to provide two examples, and if a student gives three answers, only the first two should be marked.
For questions involving calculations, the number of significant figures in candidates’ final answers should tally with that given in the question.
Chemical equations should be balanced except those in reaction schemes for organic synthesis. For energetics, the chemical equations given should include the correct state symbols of the chemical species involved.
In the question paper, questions which assess candidates’ communication skills are marked with an asterisk (*). For these questions, the mark for effective communication (1 mark per question) will be awarded if candidates can produce paragraph-length answers which are easily understandable. No marks for effective communication will be awarded if the answers produced by candidates are written in note form, and/or contain a lot of irrelevant materials.
Part I Marks 1. (a) (i) or, ZnO + H2SO4 → ZnSO4 + H2O ZnO + 2H+ → Zn2+ + H2O 1 (1) 1 1 (1) (3) (b) Remove a drop of the solution with a glass rod, and see whether any solid forms when the drop cools. (Accept other correct answers.) 1
(ii) Unreacted ZnO(s) can be seen. (iii) To ensure that the product is not contaminated with sulphuric acid. or, The unreacted ZnO(s) can be removed by filtration, but it is difficult to remove the excess H2SO4(aq).
(1) (c) Washing with distilled water can remove the water-soluble impurities. Using a small amount of water / cold water helps reduce loss of the salt. 1 1 (2) 1 (1) (1) (1)...