HCI_H1 Chem Prelim P2

NAME: _______________________________________ CT: ___________ HWA CHONG INSTITUTION C2 PRELIMINARY EXAMINATIONS H1 CHEMISTRY 8872 PAPER 2 This question booklet consists of 12 printed pages. 10 September 2008 2 hr INSTRUCTIONS TO CANDIDATES 1. This paper consists of 12 printed pages. You should also have a Data Booklet and a set of writing paper. 2. Answer all questions in Section A (Structured Questions) in the spaces provided in this Answer Booklet. 3. Answer any two questions in Section B (Free Response Questions) on the writing paper provided. Begin each question on a FRESH sheet of writing paper. 4. At the end of the examination, hand in this answer booklet and your answer scripts to Section B SEPARATELY. INFORMATION FOR CANDIDATES The number of marks is given in brackets [ ] at the end of each question or part question. You may use a calculator. You are reminded of the need for good English and clear presentation in your answers. FOR EXAMINERS’ USE ONLY TOTAL Multiple Choice Section A (Structured) Section B (Free Response) Q1 / 8 Q5 / 20 Q2 / 7 Q6 / 20 Q3 / 13 Q7 / 20 Q4 / 12 / 30 Subtotal / 40 Subtotal / 40 110

Section A Answer all the questions in this section in the spaces provided. 1(a) Molecules of NH3, H2O and HF contain polar covalent bonds. (i) State what is meant by each of the following terms: covalent bond: _______________________________________________________ ___________________________________________________________________ polar bond: _________________________________________________________ ___________________________________________________________________ (ii) Arrange NH 3, H 2O and HF in order of increasing polarity of the bond in the molecules. Explain your answer. ___________________________________________________________________ ___________________________________________________________________ ___________________________________________________________________ [4] (b) The boiling points of the hydrides of some Period 2 elements are shown in the table below. Compound CH4 NH3 H2O HF Boiling point / oC -164 -33 100 19.5 With the aid of a simple diagram, explain why the boiling point of either H2O or HF is much higher than that of methane. _______________________________________________________________________ _______________________________________________________________________ _______________________________________________________________________ [2] 2008 HCI C2 H1 Chemistry Preliminary Examination / Paper 2 2

(c) When a NH 3 molecule reacts with H +, an NH 4 + ion is formed. Draw the structure of the NH4 + ion and state the bond angle. Bond angle = _____________ [2] [Total: 8] 2(