NYJC 2015_H1_CHEM_P2_Answer Prelims

[Turn over NANYANG JUNIOR COLLEGE JC 2 PRELIMINARY EXAMINATION Higher 1 CANDIDATE NAME ANSWERS CLASS TUTOR’S NAME CHEMISTRY 8872/02 Paper 2 16 September 2015 2 hours Candidates answer Section A on the Question Paper. Additional Materials: Answer Paper Data Booklet Graph Paper READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. The use of an approved scientific calculator is expected, where appropriate. Section A Answer all the questions. Section B Answer two questions on separate answer paper. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use Section A B5 B6 B7 Total This document consists of 15 printed pages.

2 H1 Chemistry 8872/02 NYJC J2/2015 Prelim Section A Answer all the questions in this section in the spaces provided. 1 (a) Predict and explain which of the following isomers has a higher solubility in water. C C H CH2OHNH2 CH3 C C H CH2OHCH3 NH2 Isomer A Isomer B [3] Isomer B is more soluble in water. Isomers A and B both have simple molecular structures with hydrogen bonding between molecules. There is intramolecular hydrogen bonding in isomer A as the –OH and –NH2 groups are close to each other (and hence, less intermolecular hydrogen bonding). More energy is required to overcome the more extensive intermolecular hydrogen bonding between isomer B. (b) (i) Draw the ‘dot-and-cross’ diagram of NH2OH. (ii) Using VSEPR theory, e xplain why the bond angle about the N atom is greater than the bond angle about the O atom. About N atom – 3 bond pairs, 1 lone pair About O atom – 2 bond pairs, 2 lone pairs Lone pair-lone pair repulsion is greater than lone pair-bond pair / bond pair-bond pair repulsion. [3] [Total: 6]

3 H1 Chemistry 8872/02 NYJC J2/2015 Prelim [Turn over 2 (a) Describe the bonding in ethene in terms of orbital overlap. You may draw a diagram to illustrate your answer. Each C atom forms 2 sigma bonds with 2 neighbouring H atoms and 1 sigma bond with the other C atom when their orbitals overlap head -on. The two C atoms forms a pi bond when their p orbitals overlap side-on above and below the plane of the molecule. C H H bond C H H bond bond bond bond (b) (i) Ethene can be converted into ethane -1,2-diol. State the reagents, conditions and type of reaction for this reaction. reagents: dilute KMnO4, H2