Practical 7 Continuous Monitoring

Question 1

Describe how you can determine the order with respect to NaOH in the hydrolysis of methylethanoate ester [6]
CH3COOCH3 + NaOH → CH3COONa + CH3OH
Stage 1 method

Answer 1

1a- Add 50cm3 of 1 moldm-3 CH3COOCH3 to a 250cm3 beaker + 50cm3 of 1 moldm-3 NaOH, start the timer.
1b – Every 30 seconds, transfer 5cm3 sample from mixture to a clean 250ml conical flask using a 10ml measuring cylinder and teat pipette
1c – Quench the reaction by adding 20cm3 of cold water
1d – Titrate sample with 1moldm-3 HCl in burette to determine the concentration of NaOH

Question 2

Describe how you can determine the order with respect to NaOH in the hydrolysis of methylethanoate ester [6]
CH3COOCH3 + NaOH → CH3COONa + CH3OH
Stage 2 use of results

Answer 2

2a – Plot the concentration of NaOH /moldm-3 (y axis) vs time/secs (x axis)
2b – Draw tangents t=30 secs & t=60 secs and calculate the gradients
2c – Rate = gradient which will allow you to determine the rate at two different concentrations

Question 3

Describe how you can determine the order with respect to NaOH in the hydrolysis of methylethanoate ester [6]
CH3COOCH3 + NaOH → CH3COONa + CH3OH
Stage 3 analysis

Answer 3

3a – Compare the change in concentration to change in rate.
3b – If the conc is x ½ and the rate x ½ = 1st order wrt NaOH as the concentration is directly proportional to rate.
3c – If the conc is x ½ and the rate decreases by x ¼ = 2nd order wrt NaOH as concentration2 is directly proportional to rate.
3d – If conc is x ½ and rate does not change, 0 order wrt to NaOH.