9701/52/F/M/16 | A-Level Chemistry | CIE

1 Propanone, CH3COCH3, is an organic liquid which is soluble in water. Aqueous propanone reacts with aqueous iodine. The reaction is catalysed by H+(aq) ions. CH3COCH3(aq) + I2(aq) → CH3COCH2I(aq) + HI(aq) The order of reaction with respect to iodine can be determined experimentally. An experiment is carried out using the following solutions. • solution A, 25.0 cm3 of 1.00 mol dm–3 CH3COCH3(aq) • solution B, 25.0 cm3 of 1.00 mol dm–3 H2SO4(aq) • solution C, 50.0 cm3 of 0.200 mol dm–3 I2(aq) The solutions are mixed to start the reaction. At certain time intervals, a 10.0 cm3 portion of the mixture is withdrawn and transferred to a conical flask containing excess sodium hydrogencarbonate, NaHCO3(aq). This prevents any further significant reaction taking place by removing the H+(aq) ions. The concentration of unreacted I2(aq) in each 10.0 cm3 portion of the mixture can then be determined by titration with aqueous thiosulfate ions, S2O3^2–(aq).