Question

The lab is the acid catalysed hydrolysis of ethyl acetate.

Experimental

1. Pipette 100.0 cm³ of 0.5 M HCl into a conical flask (labeled A) and a further 20.0 cm³ into a second conical flask (labeled B).
2. Prepare 25 cm³ of crushed-ice/water. Pipette 5.0 cm3 of ethyl acetate into flask A, shake well, start the stop watch and immediately withdraw 5.0 cm³ of the solution. Immediately, run this into the crushed-ice water mixture, and swirl to 'stop' the reaction, and as soon as possible titrate with the NaOH solution. Without ever stopping the watch, note the time to the nearest second at which the solution is run into the ice/water mixture. This is the first time, t₁, of the series.
3. About 10 min after the first withdrawal, pipette another 5.0 cm³ of the reaction mixture from the flask and titrate as before, again noting the exact time, t₂, that the reaction is 'stopped'.
4. Further titrations are made at times of about 20, 30, 40, 60, 80, 100 and 120 min.
5. The reaction is accelerated to completion by heating to 70°C for ½ hr. During this time the flask must be stoppered to avoid changes in concentration due to evaporation. Cool to room temperature, pipette 5.0 cm³ and add to 25 cm³ of water and titrate as before.
6. For a control, take flask B and add 1 cm³ of water, pipette 5.0 cm³ and titrate as before.

Calculation

The initial ethyl acetate concentration is proportional to (V_∞ - V_o), where V_∞ is the final titre volume for flask A and V_o is the titre volume for flask B. The concentration of ethyl acetate at time t is proportional to (V_∞ - V_t) where V_t is the titre volume of the sample at time t. Plot ln(V_∞ - V_t) against time. Hence determine the value of k₁ (in s^-1) and the half-life of the reaction.
Question

1. If the temperature of the reaction increased by about 2°C during the course of the reaction, what effect would this have on the points plotted?
2. Assume the activation energy, E_a, to be about 11 kJ mol^-1, calculate the fractional variation in the rate constant that would result from this increase in temperature.

Answer 1