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 units. [2] (b) By means of calculations, predict whether a precipitate will form when 25.0 cm 3 of 0.0100 mol dm-3 strontium nitrate is mixed with 20.0 cm 3 of 0.0150 mol dm -3 sodium fluoride. [3] [Total: 5] 3 Ethylenediamine tetra-acet ate (edta) forms hexacoordinate complexes with many divalent metal ions. (a) On the diagram below, circle the six atoms of edta that form bonds with the metal ion. [1] CH 2C O O - CH 2C O O - NC H 2 CH 2 N CH 2 CH 2 C O O - C O O - edta

4 (b) (i) Describe and explain what is seen when NH 3(aq) is added dropwise to CuSO4(aq) until no further change is observed. [4] ( i i ) When a small amount of aqueous edta is added to the resulting mixture in (b)(i), the solution turns pale blue. Stat e the type of reaction that has taken place and write an equation for the reaction. [2] (c) Cadmium ions are poisonous; they can c ause bone porosity by replacing the calcium ions in bones. One treatment for cadmium poisoning involves administering a solution of edta. Calcium and zinc are essential for health. Ca2+ + edta4- ⇌ [Ca(edta)]2- K c = 5 x 1010 mol-1 dm3 Cd2+ + edta4- ⇌ [Cd(edta)]2- K c = 6 x 1016 mol-1 dm3 Zn2+ + edta4- ⇌ [Zn(edta)]2- K c = 3 x 1016 mol-1 dm3 (i) Comment on the use of edta as a treatment for cadmium poisoning in the light of the data provided. [1]

5 ( i i ) Suggest a problem that might arise during the treatment. [1] [Total: 9] 4 (a) (i) The decomposition of hydrogen peroxide proceeds in two steps as shown below: H2O2 → H2O + O slow O + H2O2 → H2O + O2 fast Write the rate equation for this reaction. [1] (ii) Using your answer to (a)(i) and the axes provided, sketch the graphs of rate against [H 2O2] and [H2O2] against time to show the order of reaction clearly. [2] [H2O2] rate [H 2O2] time

6 (b) Aqueous hydrogen peroxide is fairly stable but, when a mixture of cobalt(II) salt and tartaric acid, HOOCCH(OH) CH(OH)COOH, is added to hydrogen peroxide, oxygen is vigorously evolved. Co2+ + ½H2O2 + H+ → Co3+ + H2O Eθ = -0.05 V Co3+ + ½H2O2 → Co2+ + ½O2 + H+ Eθ = +1.14 V (i) State the role of cobalt( II) in this reaction. What property of cobalt makes it suitable for this function? [2] ( i i ) Suggest a role for the tartaric acid in the reaction. [1] [Total: 6] 5 For each of the following pairs of compounds, describe a simple chemical test which would enable you to distinguish between them. Describe the observations and write equations for the reactions involved. [6] (a) CH3 CH3 CONHCH2CH3 CH3 CH3 NHCOCH2CH3 and

7 (b) NH O NH O and [Total: 6] 6 (a) Consider the following reaction scheme, starting from 2-phenylethanol. CH2CH2OH Step 1 Step 2 Step 3 Step 4 NO2 CH2CH2OH NO2 CH2CHO CH2CH(OH)COOH NO2 A (i) Draw the structure of A in the box provided. [1]

8 ( i i ) State reagents and conditions for Steps 1 – 4. [4] Step 1 Step 2 Step 3 Step 4 (b) State the types of reactions occurring in Steps 3 and 4. [2] Step 3 : ___________________________________ Step 4 : ___________________________________ (c) Describe the mechanism of Step 1. [3] [Total: 10]

9 7 Xanthoangelol J is a member of the chalcone fami ly, isolated from the stem of Angelica Keiskei. It is found to have antitumour and antimetastatic activities. O C H3 CH3 C H3 OH OH O H OH Xanthoangelol J (a) State four functional groups, other than phenyl group, present in Xanthoangelol J. [2] (b) Describe what you would ex pect to observe when Xanthoangelol J reacts with the following reagents.