SAJC_H2_CHEM_P3

2 Answer any four questio ns 1 (a) Acidified potassium manganate, KMnO4, is a strong oxidising agent which can oxidise both X2+ and C2O4 2- in XC2O4. One of the products of this reaction is CO2. 15.00 cm3 of 0.1 mol dm-3 acidified KMnO4 was found to completely oxidise 25.0 cm3 of 0.1 mol dm-3 XC2O4 solution. (i) Write a balanced equation for the reaction between MnO4 - and C2O4 2- only. Hence, determine the volume of KMnO4 needed to oxidise C2O4 2- only. (ii) Using your answer in (a)(i), find the oxidation state of X in the product. [5] (b) The following table lists the boiling points of some organic compounds. Compound Formula M r Boiling point / °C A CH3CH2CH2CH2OH 74 118 B CH3CH2CH2CH2CH3 72 36 C 191 130 By reference to the type and extent of relevant intermolecular forces, explain the differences in boiling points between A and B and between A and C. [4] (c) The elements Y and Z can be one of the following: Na, Mg, A l, Si and P. Both the chloride and oxide of Y can react with aqueous sodium hydroxide. The oxide of Y can also react with aqueous hydrochloric acid. Element Z has a chloride and an oxide and both react vigorously with water to form a solution of pH = 2. Identify the elements Y and Z. Explain the above observations with the help of relevant balanced equations. [5] [Turn over

3 1 (d) Suggest a simple chemical test to distinguish between each pair of compounds. State the reagents and conditions needed and give the expected observations for each compound. (i) CH3CH2CCH2OH O and CH3CCH2CH2OH O P Q (ii) and R S [4] (e) Suggest a synthesis to convert CH 2=CHCH2Br into CH2=CHCHO. Include all reagents and conditions and draw all intermediates formed. [2] [Total：20]

4 2 2 (a) In one compartment of a voltaic cell, a graphite rod dips into an acidic solution of K2Cr2O7 and Cr(NO3)3. In the other compartment, a tin bar dips into a Sn(NO3) solution. A KNO3 salt bridge joins the two compartments. (i) Draw an apparatus diagram to show the set up of the cell. In your diagram, include the direction which electrons flow when the two compartments are connected by a wire. (ii) Give one use of the KNO 3 salt bridge in the set up. (iii) Write an equation for the overall cell reaction and calculate the overall cell potential under standard conditions. (iv) If a current of 0.2 A is drawn from the cell for 2.5 hours, what is the change in mass of the tin bar? [8] (b) (i) When iodide ions ( I-) and peroxodisulfate ions (S2O8 2-) are mixed, the reaction proceeds at a very slow rate. However, when aqueous CoCl3 is added, the reaction speeds up, pro