2019 H2 Chem Planning Qn Ans

1 N2019 A level Planning Question_Suggested Solutions (a) Procedure 1. Using a 50 cm3 measuring cylinder, transfer 30 cm3 of I2(aq) into a 250 cm3 beaker. To the same beaker, add 30 cm3 of H2SO4(aq) using another 50 cm3 measuring cylinder. 2. Measure 30 cm3 of CH3COCH3(aq) into a 50 cm3 measuring cylinder. 3. Add the CH3COCH3(aq) into the same 250 cm3 beaker in step 1. Start the stopwatch immediately. Stir the mixture using a glass rod to ensure even mixing. 4. Using a 10.0 cm3 pipette, transfer 10.0 cm3 of the reaction mixture into a 250 cm3 conical flask. At time 2 min, add 10 cm 3 of NaHCO3(aq), measured using a 10 cm 3 measuring cylinder, into the 250 cm3 conical flask. 5. Immediately titrate the iodine present in the conical flask against Na2S2O3(aq) from a burette, until the solution turns pale yellow. Add 1 cm3 starch from a dropper and continue the titration until the blue-black solution in the conical flask turns colourless. 6. Repeat steps 4 and 5 at 6, 10, 14, 18, 22, 26 minutes. 7. Record the titration results in a suitable table. (b) The volume of Na2S2O3 used for titrating a sample of quenched aliquot at time t is proportional to the concentration of I2 present in the reaction mixture at time t. Since the gradient of the graph is constant with a negative value, the rate of reaction is constant. Hence, the order of reaction with respect to iodine is zero since the reaction rate is independent of the concentration of iodine. volume of sodium thiosulfate time