4 Techniques to investigate rates of reaction PAG9 PAG10

Techniques to investigate rates of reaction measurement of the change in volume of a gas Titrating samples of reaction mixture with acid, alkali, sodium thiosulphate etc Colorimetry. Measurement of optical activity. Measurement of change of mass Measuring change in electrical conductivity H2O2 (aq) + 2I- (aq) + 2H+ (aq)  2H2O(l) + I2 (aq) HCOOCH3 (aq) + NaOH(aq)  HCOONa(aq) + CH3OH(aq) (CH3 )2C=CH2 (g) + HI(g) (CH3 )3CI(g) BrO3 – (aq) + 5Br – (aq) + 6H+ (aq)  3Br2 (aq) + 3H2O(l) HCOOH(aq) + Br2 (aq)  2H+ (aq) + 2Br – (aq) + CO2 (g) HCOOH(aq) + Br2 (aq)  2H+ (aq) + 2Br – (aq) + CO2 (g) There are several different methods for measuring reactions rates. Some reactions can be measured in several ways This works if there is a change in the number of moles of gas in the reaction. Using a gas syringe is a common way of following this. If drawing a gas syringe make sure you draw it with some measurement markings on the barrel to show measurements can be made. This works if there is a gas produced which is allowed to escape. Works better with heavy gases such as CO2 HCOOH(aq) + Br2 (aq)  2H+ (aq) + 2Br – (aq) + CO2 (g) CH3COCH3 (aq) + I2 (aq) → CH3COCH2 I(aq) + H+ (aq) + I– (aq) Small samples are removed from the reaction mixture, quenched (which stops the reaction) and the titrated with a suitable reagent. The NaOH could be titrated with an acid The H+ could be titrated with an alkali The I2 could be titrated with sodium thiosulphate If one of the reactants or products is coloured then colorimetry can be used to measure the change in colour of the reacting mixtures The I2 produced is a brown solution Can be used if there is a change in the number of ions in the reaction mixture If there is a change in the optical activity through the reaction this could be followed in a polarimeter CH3CHBrCH3 (l) + OH− (aq)  CH3CH(OH)CH3 (l) + Br− (aq)