SRJC 2008 JC2 Prelim H2 Paper 2

© SRJC 2008 9746/02/Prelims/2008 [Turn Over SERANGOON JUNIOR COLLEGE General Certificate of Education Advanced Level Higher 2 CANDIDATE NAME CLASS INDEX NUMBER CHEMISTRY 9746/02 Preliminary Examination 25 August 2008 Paper 2 1 hr 30 min Additional Materials: Data Booklet Writing Papers READ THESE INSTRUCTIONS FIRST Write your name and class on all the work you hand in. Write in dark blue or black pen on both sides of the paper. You may use a soft pencil for any diagrams, graphs or rough work. Answer all questions in the space provided. At the end of the examination, fasten all your work securely together. The number of marks is given in the brackets [ ] at the end of each question or part questions. For Examiner’s Use 1 2 3 4 5 Total This document consist of 12 printed pages and 0 blank page

2 © SRJC 2008 9746/02/Prelims/2008 [Turn Over 1 Potassium manganate (VII) is an oxidising agent used in redox titrations. A 50.0 cm 3 sample of iron ( II) oxalate, FeC 2O4, was dissolved in water and the solution made up to 250 cm 3. A 25.0 cm 3 portion of this solution was acidified and titrated with 20.80 cm3 of 0.025 mol dm-3 potassium manganate (VII). (a) (i) State the change in oxidation number for manganese. (ii) Write an ionic equation for the oxidation of oxalate ion to carbon dioxide. (iii) Write an overall equation for the reaction between potassium manganate (VII) and iron (II) oxalate. (iv) Calculate the concentration of iron (II) oxalate in the original sample. (v) State the colour change at t he end point of the titration. [5]

3 © SRJC 2008 9746/02/Prelims/2008 [Turn Over In the above redox titration, carbon dioxid e gas is produced. One of the uses of carbon dioxide is in the manufacture of carbonated drinks. Cola, a carbonated drink, was originally invented by chemist, John Pemberton, to stop headaches and calm nervousness. Cylinders of pressurised carbon dioxi de are used to produce cola. A commercial cola drink was manufactured using such cylinde rs, each with internal volume of 5 dm 3 and contains 2.58 kg of carbon dioxi de. The pressure inside each of the cylinder was found to be 1.0 x 104 kPa at room temperature. A glass of cola is fizzy because carbon dioxide has been dissolved in it under pressure. When 500 cm 3 of commercial cola drink is poured out from a bottle, the carbon dioxide is gradually released as bubbles of gas . On evolution of 1 dm 3 of carbon dioxide, the cola went flat, as the concentration of dissolved carbon dioxide decreases to its saturation level of 1.5 g dm -3 at room temperature. (b) (i) Using the ideal gas equation pV = nR T, calculate the pressure the carbon dioxide would exert inside the cylinder at room temperature. (ii) Suggest why the pressure you calculated in b(i) differs from the actual value. (iii) Calculate the total mass of carbon dioxide dissolved in the 500 cm 3 bottle of cola under pressure. (iv) Determine the number of 500 cm 3 bottles of cola that could be manufactured using one cylinder of pressurised carbon dioxide. [5] [ T o t a l : 1 0 ]

4 © SRJC 2008 9746/02/Prelims/2008 [Turn Over 2(a) Brine is water saturated or nearly saturated with sodium chloride salt, NaC l, and was historically used to preserve vegetables, fish, and meat. Brine is electrolysed in the chloralkali pr ocess to make sodium hydroxide, chlorine and hydrogen, as well as the hypochlorite and chlorate salts on an industrial scale. In this case, the chloride ions are oxidised to chlorine, while water is reduced to hydrogen gas and hydroxide ions. (i) Write the reactions that occur at the anode and the cathode and hence the overall equation for the electrolysis of brine. Anode : Cathode : Overall : (ii) During a random sampling it was found that sodium chlorate (I) was detected. Write a chemical equation to illustrate a possible reaction that causes this observation. (iii) The volume of chlorine gas collected 3 hours after the chloralkali process was 2700 cm 3. Assuming there is no contamination to the chlorine gas collected and the process efficiency was 80%, Calculate the current required to produce the specified quantity of chlorine gas at room temperature. [4]

5 © SRJC 2008 9746/02/Prelims/2008 [Turn Over (b) Sedoneural is sodium bromide salt and is widely used as an anticonvulsant and a sedative. Write the chemical equati ons when concentrated sulphuric acid was warmed with sodium bromide. [2] (c) Hydrogen halides are formed from the chemical reaction of hydrogen with one of the halogen elements ( fluorine, chlorine, bromine, iodine), which are found in Group VII of the periodic table. Hydrogen halides can be abbreviated as HX where H represents a hydrogen atom and X represents a halogen (fluorine, chlorine, bromine or iodine). Upon dissolving the hydrogen halides in water, acids are formed. (i) With reference from the Data Booklet , explain and rank the pK a of the following acids: HI, HBr and HCl. (ii) What would you expect to see when hy drobromic acid reacts with aqueous silver nitrate followed by concentrated ammonia? (iii) Explain your observation made in c(ii) when concentrated ammonia was added. Include equations in your answer [6] [Total: 12]

6 © SRJC 2008 9746/02/Prelims/2008 [Turn Over 3(a) Copper and iron are in the same period with chromium and are essential in all plants and animals. Most mollusks (suc h as mussels and scallops) and some arthropods (such as horseshoe crab and blue crab) use the copper-containing pigment hemocyanin rather than iron-containing haemoglobin for oxygen transport. (i) Comment on values of the first ionisation energy of copper and iron as given in the Data Booklet with the aid of appropriate electronic configurations. (ii) A sample of oxygenated horseshoe cr ab blood and chicken blood was analysed and the absorption spectrum was observed. Legend: A: Chicken blood B: Horseshoe crab blood Colour Wavelength (nm) Violet 380 – 450 Blue 450 – 495 Green 495 – 570 Yellow 570 – 590 Orange 590 – 620 Red 620 – 750 Suggest from the spectrum and the data av ailable the colour of the oxygenated horseshoe blood and explain why this colour arises.

7 © SRJC 2008 9746/02/Prelims/2008 [Turn Over (iii) Explain, with aid of appr opriate equations, what you will observe when dilute ammonia is gradually added until in excess to an extract of oxygenated horseshoe blood containing Cu2+(aq) ions. [9] (b) Iron is an important compone nt of several biological molecules especially in haemoglobin. What is the function of haemoglobin in the body and how does it carry out this function? [3]

8 © SRJC 2008 9746/02/Prelims/2008 [Turn Over (c)(i) A half-cell containing copper el