MJC H2 CHEM P2 QP Prelim

Name: _______________________ Class: 13S_________ Reg Number: ______ MERIDIAN JUNIOR COLLEGE Preliminary Examination Higher 2 _______________________________________________________________________________ Chemistry 9647/02 Paper 2 Structured Questions 19 September 2014 2 hours Additional Materials: Data Booklet _______________________________________________________________________________ INSTRUCTIONS TO CANDIDATES Write your name, class and register number in the spaces provided at the top of this page. Write your calculator brand and model/number in the box provided above. Answer all questions in the spaces provided on the question paper. All working must be shown clearly. INFORMATION FOR CANDIDATES This document consists of 20 printed pages. Examiner’s Use Paper 1 MCQ / 40 Paper 2 Q1 / 12 Q2 / 12 Q3 / 11 Q4 / 13 Q5 / 14 Q6 / 10 Paper 3 / 80 Total / 192 Percentage Grade The number of marks is given in brackets [ ] at the end of each question or part question. You are reminded of the need for good English and clear presentation in your answers. Calculator Model / No.

2 [Turn over 1 Planning (P) The enthalpy change of neutralisation is the enthalpy change when one mole of water is formed in the reaction between an acid and a base. H+(aq) + OH−(aq)  H2O(l) You are required to determine the enthalpy change of neutralisation between a strong base and a carboxylic acid through a series of experiments. You may assume you are provided with the following:  FA 1, aqueous sodium hydroxide, NaOH  FA 2, 1.50 mol dm–3 propanoic acid, CH3CH2COOH  polystyrene (styrofoam) cups  apparatus normally found in a school laboratory. In separate experiments, different volumes of FA 1 and FA 2 are mixed while keeping the total volume of the reaction mixture constant. In each experiment, the temperature rise, ∆T , is to be determined. When a graph of ∆T against volume of FA 1 used is plotted, it is observed that the t emperature rise will increase, and then decrease when different volumes of FA 1 are used. Data from the graph can then be used to determine:  the concentration of sodium hydroxide, NaOH, in FA 1.  the enthalpy change of neutralisation between NaOH and CH3CH2COOH. It is given that 4.18 J is required to raise the temperature of 1 cm 3 of any solution by 1 oC. (a) The total volume of the reaction mixture between FA 1 and FA 2 is constant. Explain why the temperature rise increases as more FA 1 is added to the mixture. [1] (b) It is predicted that the maximum temperature change for the neutralisation would occur when the volume of FA 1 mixed is between 35 cm3 and 40 cm3. Write a detailed plan on how you could determine the temperature changes for the series of reactions between FA 1 and FA 2. The volume of FA 1 used should be between 30 cm 3 and 45 cm 3 while the total volume of any mixture should be kept constant at 70 cm3. Comment [M1]: Shifted the sentence down to make the flow of the question better.

3 [Turn over Your plan should contain the following:  all essential experimental details  appropriate volumes of solutions to be used  a tabulation of the experimental data to be collected (on the next page) ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… ………………………………………………………………………………………………… …………………………………………………………………………………………………

4 [Turn over Tabulation: [6] (c) (i) The following plots were plotted on a grid after an experiment. Draw suitable graphs through the plotted points. 30 50 45 40 35 Volume of FA 1 / cm3 10.0 9.0 8.0 7.0 6.0 5.0 4.0 ∆ T / oC

5 [Turn over (ii) By using the graph in (i), calculate:  the concentration of sodium hydroxide in FA 1.  the enthalpy change of neutralisation between NaOH and CH3CH2COOH. [4] (d) Describe one major source of error for the experim ent and suggest an improvement which could significantly increase the accuracy of the experiment. [1] [Total: 12]

6 [Turn over 2 Chlorine is a yellow -green gas that was first synthesi sed around 1630. Nearly all the chlorine in the Earth's crust occurs as chloride in various ionic compounds. It forms a variety of oxides such as chlorate (V), C lO3 – , chlorate(III), ClO2 – , and chlorine dioxide, ClO2. The table below shows the reduction potentials for some oxides of chlorine. Electrode Reaction Eo / V ClO3 – (aq) + H2O(l) + 2e – ClO2 – (aq) + 2OH – (aq) +0.33 ClO3 – (aq) + 2H+(aq) + e – ClO2(g) + H2O(l) +1.15 ClO2(g) + 4H+(aq) + 5e – Cl–(aq) + 2H2O(l) +1.50 (a) Draw a labelled diagram to show how the redox potential Eo(ClO3 – / ClO2) could be measured in the laboratory. [2]

7 [Turn over (b) Use the Data Booklet and the above information to predict what might happen when solutions of the two reagents are mixed together. In each case , calculate the Eo cell and write an overall equation for any reaction that occurs. (i) mixing ClO3 – (aq) with excess H2O2(aq) (ii) mixing ClO2 (g) with Fe2+ (aq). [4] Comment [M2]: Follow A-level phrasing N2004 P3 Q2

8 [Turn over (c) It was found that chlorine gas has a density of 3.04 kg m–3 at a temperature of 15 oC and a pressure of 1 atm. (i) Assuming ideal behavior, calculate the relative molecular mass of chlorine. (ii) Comment on the theoretical relative molecular mass of chlorine and that obtained in (i). Suggest reason for any discrepancy observed. (iii) Under what conditions of temperature and pressure would the behavior of real gases be more ideal? (iv) On the axes below, sketch the expected graph of density/pressure, P  , against temperature, T, for an ideal gas. P  T [4]

9 [Turn over (d) Chlorine dioxide, C lO2, is a useful agent in water treatment. Very pure chlorine dioxide is produced by electrolysis of aqueous sodium chlorate(V), NaClO3. Calculate the current needed to produce 1 tonne of ClO2 gas per day. (1 tonne = 1000 kg) [2] [Total: 12] 3 Copper and cobalt are common transition elements. (a) By quoting appropriate data from the Data Booklet, (i) explain the difference between the atomic radii of copper and cobalt. (ii) suggest an element in Period 2 that requires approximately simi lar energy to produce its ion in the +2 oxidation state as that of copper. [3]

10 [Turn over (b) Various potassium salts are known, some of which include anions containing cobalt complexed with cyanide ions, CN–. Salt A has an empirical formula of K 4CoC4N4. Salt B has a composition by mass of K, 35.3%; Co