PJC_H2 Chemistry_2008 JC2 H2 Chemistry Prelim Paper 2

Name: Index No.: CT Group: 07 PIONEER JUNIOR COLLEGE JC2 PRELIMINARY EXAMINATION 2008 CHEMISTRY 9746/02 Higher 2 Paper 2 Structured 16 September 2008 1 hour 30 minutes Additional Materials: Data Booklet READ THESE INSTRUCTIONS FIRST Write your name, CT Group and index number in the spaces at the top of this page. Write in dark blue or black pen. Answer all questions. Write your answers in the spaces provided on the question paper. A Data Booklet is provided. You may use a calculator. The number of marks is given in brackets [ ] at the end of each question or part question. FOR EXAMINER’S USE Question Question 1 / 8 5 / 6 2 / 5 6 / 10 3 / 9 7 / 6 4 / 6 8 / 10 Total / 60 This document consists of 12 printed pages. [Turn Over

2 Answer all questions. Write your answers in the spaces provided. 1 (a) Nitrogen and phosphorus are elements of Group V in the Periodic Table. Nitrogen exists naturally as gaseous diatomic N ≡N molecules whereas phosphorus is a solid and exists as P 4 molecules comprisi ng of P-P single bonds. (i) Account for the difference in their physical states in terms of structure and bonding. [2] ( i i ) Suggest why phosphorus does not occur naturally as P ≡P molecules. [1] (b) Nitrate, NO 3 -, and phosphate, PO4 3-, are oxoanions of nitrogen and phosphorus respectively. (i) Draw dot-and-cross diagram s to show the bonding NO 3 - and PO 4 3-. Hence, deduce the shapes and state the bond angles around the nitrogen and phosphorus atom. [4] ( i i ) Explain why it is not possible fo r nitrogen to form an oxoanion with formula of NO 4 3-. [1] [Total: 8]

3 2 (a) Strontium fluoride, SrF2, is sparingly soluble in water. The solubility of strontium fluoride in water at 25 oC is 0.073 g dm -3. Calculate the solubility product, Ksp, of strontium fluoride, stating the uni