DHS Prelim P2 Qn

This document consists of 19 printed pages and 1 blank page.  DHS 2015 [Turn over Name: Index Number: Class: DUNMAN HIGH SCHOOL Preliminary Examination 2015 Year 6 H2 CHEMISTRY 9647/02 Paper 2 Structured Questions 16 September 2015 2 hours Additional Materials: Data Booklet INSTRUCTIONS TO CANDIDATES 1 Write your name, index number and class on this cover page. 2 Answer all questions. 3 Write your answers in the spaces provided on the Question Paper. 4 The use of an approved scientific calculator is expected, where appropriate. 4 A Data Booklet is provided. 5 The number of marks is given in brackets [ ] at the end of each question or part question. Question No. 1 (P) 2 3 4 5 6 7 Total % Marks 12 15 15 6 9 10 5 [72]

2  DHS 2015 9647/02 [Turn over Answer all the questions in the spaces provided. 1 Planning (P) (a) Part (a) is on the rate of effusion of gas. If a container of gas has a tiny hole in it, the gas will gradually escape through the hole. This process is called effusion and the rate at which it occurs is called the rate of effusion. A student has carried out a series of preliminary experiments to investigate how the rate of effusion depends on the relative molecular mass, M r, of a gas. She found that the rate of effusion is halved when the Mr of a gas is doubled. (i) Using the apparatus shown below, plan a laboratory experiment to verify the student’s findings. The experiment will involve using different gases where their rate of effusion will be determined, bearing in mind that temperature will also affect the effusion rate of the gas. In addition to the standard apparatus present in a laboratory you are provided with the following:  access to samples of hydrogen, butane, oxygen, carbon dioxide and chlorine gases Your plan should include:  brief, but specific, details of the apparatus you would use;  how you ensure the syringe only contain the gas you are investigating;  how you would measure the effusion time;  how you produce reliable results;  steps taken to ensure other factors are controlled;  a table with appropriate headings to show the data you would record when carrying out your experiment and the values you would calculate in order to construct a graph to support or reject the statement. The headings must include the appropriate units. Retort stand clamp

3  DHS 2015 9647/02 [Turn over Table [You need not use all the columns in the following table.]

4  DHS 2015 9647/02 [Turn over (ii) Sketch a graph you would plot using your measured or calculated data obtained in (a)(i) and describe how you would use the graph to determine the effusion rate of nitrogen gas (Mr = 28.0). You may assume that the student’s findings is accurate. [8] (b) Part (b) is on the synthesis of an inorganic compound. The compound, Cu(NH 3)4SO4, can be synthesised in the laboratory by gradually adding aqueous ammonia to an aqueous solution of copper(II) sulfate. The blue solution will turn a deeper blue colour. The mixture should be allowed to stand for about 15 minutes. Deep blue crystals will be deposited by addition of cold acetone (an organic solvent) and the mixture be allowed to stand in cold for another 15 minutes. Cu(H 2O)6 2+ + 4NH3 Cu(NH3)4 2+ + 6H2O You may assume that you are provided with the following chemicals:  60 cm 3 aqueous solution of copper(II) sulfate, of concentration 0.50 mol dm–3;  aqueous ammonia, of concentration 2.0 mol dm –3  50 cm 3 acetone (i) Calculate the minimum volumes of:  copper( II) sulfate solution;  aqueous ammonia; required for the preparation of 5 g of Cu(NH3)4SO4 (Mr = 227.6).

5  DHS 2015 9647/02 [Turn over (ii) Write a plan for the preparation of approximately 5 g of Cu(NH3)4SO4. In your plan you should give a full description of the procedures you would use to prepare and purify the product. Details on confirming the identity of the product are not required. [4] [Total: 12]

6  DHS 2015 9647/02 [Turn over 2 (a) Pure unsymmetrical dimethylhydrazine (UDMH), (CH 3)2N2H2 can be used as a rocket fuel. It is typically mixed with dinitrogen tetraoxide, N2O4. The equation for the reaction of the UDMH with dinitrogen teraoxide is given below. S = +844 J mol –1 K–1 G = –2107 kJ mol –1 (CH3)2N2H2(l) + 2N2O4(l)2 C O 2(g) + 4H2O(g) + 3N2(g) In the ascent stage of a lunar module, the total mass of propellant (UDMH and N 2O4) used in the thruster rockets was 244 kg. (i) Calculate the total volume of product gases formed from the complete reaction of UDMH at a temperature of –10 C and a pressure of 0.6 kPa, assuming that the UDMH and dinitrogen tetroxide were mixed in the molar ratio 1 : 2. The table below shows some other relevent thermodynamic data. substance H f (298 K) / kJ mol–1 (CH3)2N2H2(l) x CO2(g) –394 H2O(g) –242 N2O4(l) +9.0 . (ii) Define the term standard enthalpy change of formation of (CH3)2N2H2. (iii) Determine the value of x at 298 K. [6]

7  DHS 2015 9647/02 [Turn over (b) Dinitrogen tetroxide exists in equilibrium with nitrogen dioxide. Nitrogen dioxide itself can be decomposed into nitrogen monoxide and oxygen as shown below. 2NO 2(g) 2NO(g) + O 2(g) The rate equation for this thermal decomposition is as follows. Rate = k [NO 2]2 The rate constant, k, for the thermal decomposition was measured at five different temperatures and the results were used to plot the graph shown below. The Arrhenius equation is k = RT E a Ae  , where k is the rate constant, A is the Arrhenius constant, E a is the activation energy, R is the molar gas constant, and T is the thermodynamic temperature in Kelvins. The Arrhenius equation may also be expressed in the following form: ln k = ln A – RT aE (i) Use the graph to calculate the activation energy, Ea, for the decomposition of nitrogen dioxide, stating its units.

8  DHS 2015 9647/02 [Turn over (ii) A 3.0 dm3 vessel is filled with 6.0 mol of NO2 at a temperature of 650 K. The rate constant, k, at this temperature is 3.16 dm 3 mol–1 s–1. Calculate the initial rate of decomposition for the reaction at this temperature, stating its units. [4] (c) The first ever rocket-power fighter plane, the Messerschmitt Me 163, was powered by the reaction between a hydrazine-methanol mixture and hydrogen peroxide. (i) When hydrazine reacts with hydrogen perox ide, chemically stable products are formed. Suggest an equation for the reaction between hydrazine and hydrogen peroxide and state the change in oxidation state of the oxidised species. (ii) In a proposed electrochemical cell, hy drogen peroxide oxidises the methanol to carbon dioxide in acidic medium. Write a balanced equation for the reaction occuring at the anode and cathode. Anode : Cathode : (iii) Given that the cell is capable of producing an e.m.f. of 1.75 V. By using suitable data from the Data Booklet , calculate the standard reduction potential for the anode reaction. [5] [Total: 15]

9  DHS 2015 9647/02 [Turn over 3 This question is about calcium and nitrogen containing organic compounds. Calcium oxalate (CaC2O4) is a sparingly soluble salt but the solubility of calcium oxalate is increased by the addition of alanyl-alanine. Alanyl-alanine is a dipeptide of alanine with the structure given below. NH2 CH3 O N H OH O CH3 alanyl-alanine (a) Write a balanced equation with state symbols between the reac