NYGH 2018-S3MYE-IP Chem Ans

Class Register Number Name NANYANG GIRLS' HIGH SCHOOL Mid-Year Examination 2018 Secondary Three IP Chemistry CHEMISTRY Mark Scheme 1 hour 30 minutes Monday 7 May 2018 0845 - 1015 READ THESE INSTRUCTIONS FIRST Write your class, register number and name in the spaces at the top of this page. Do not use paper clips, glue or correction fluid. There are 3 sections in this paper. Section A Answer all questions. For each question there are four possible answers A, B, C and D. Choose the one you consider correct and record your choice in the Multiple-Choice Answer Sheet provided. Each correct answer will score one mark. A mark will not be deducted for a wrong answer. Section B and C Answer all questions. The number of marks is given in brackets [ ] at the end of each question or part question. Candidates are reminded that all quantitative answers should include appropriate units. The use of an approved scientific calculator is expected, where appropriate. Candidates are advised to show all their working in a clear and orderly manner. Section A (20 marks) Section B (30 marks) Section C (10 marks) Total (60 marks) Setter: KXY, NHK, CT This document consists of 12 printed pages. NANYANG GIRLS' HIGH SCHOOL [Turn over

2018 Mid-Year Examination Secondary Three IP Chemistry 2 Nanyang Girls’ High School Setter: KXY, NHK, CT Choose the answer you consider correct and record your choice in the Multiple-Choice Answer Sheet provided. 1 D 2 B 3 D 4 B 5 C 6 B 7 B 8 C 9 D 10 B 11 D 12 A 13 C 14 B 15 D 16 D 17 D 18 C 19 B 20 B Section A Answer all questions.

2018 Mid-Year Examination Secondary Three IP Chemistry 3 Nanyang Girls’ High School Setter: KXY, NHK, CT [Turn Over] B1 Enzymes are biological catalysts and used in research laboratories and in industries. Enzymes called proteases can break down proteins by water to amino acids. The amino acids can be separated and identified by chromatography. The diagram below shows a typical chromatogram. (a) Given that the amino acids have the following Rf values: amino acid glutamic acid glycine alanine leucine Rf values 0.4 0.5 0.7 0.9 Identify the two amino acids on the chromatogram. [2] X is glutamic acid [1] and Y is alanine [1]. (b) A locating agent is used on the chromatogram. Explain why the chromatogram must be exposed to the locating agent. [1] Locating agent is required as amino acids are colourless/ so as to make the amino acids visible/ to show the positions of the samples/ to show the distance travelled by the samples. Section B Answer all questions. Write your answers in the spaces provided. solvent front starting line for samples sample Y sample X initial level of solvent

2018 Mid-Year Examination Secondary Three IP Chemistry 4 Nanyang Girls’ High School Setter: KXY, NHK, CT (c) Suggest another method to identify the amino acids on the chromatogram other than measuring Rf values. [1]