Two details of the ester synthesis ate very unusual: 1. Esterification needs a lot of time (some days).
                                                                                      2. It is never completed (1/3 of the acid will remain).
Ester-Synthesis (Esterification)
(CH₃COOH)   +   HO-C₂H₅ ---(catalyst)---> CH₃COO-C₂H₅ + H₂O
Acetic acid       ethanol                          ester                  water
In order to measure which amount of acetic acid was consumed for ester synthesis, take samples after 1, 2, 3, ... days for neutralisation by 1M sodium hydroxide.
Material
Ampoule in which acetic acid and ethanol were mixed, insulin syringe, dropper bottles with 1M NaOH and with phenolphthalein solution, four ampoule (3 mL) for titration.
Experiment
1. Take a 1-ml syringe to transfer 0.2 ml samples of the mixture into an ampoule.
2. Add 1 drop of phenolphthalein solution as an indicator.
3 Shake while you add drops of 1M sodium hydroxide to neutralise the acetic acid remaining in the sample.
4. Write down how many drops of alkali were needed for neutralization.
5. The endpoint of neutralisation is reached when the pink colour does not longer disappear by shaking.
Observation (Photo) Consumption of 1M NaOH for neutralisation of acids in 0,2-ml samples of the mixture:
a) after mixing:  40 drops (2 ml),  after 12 hours: 20 drops (1 ml),  after 3 days: 10 drops (0.5 ml).
Explanation
  CH₃COOH(aq)     +     NaOH(aq) --------(neutralisation)----------> CH₃COONa(aq) + H₂O(l)
  Acetic acid   sodium hydroxide                        salt solution   water
Even after many days 0.5 ml of sodium 1M NaOH (= 1/4 of the initial volume) were needed for neutralisation of further samples. So 1/4 of the acid was still present in the mixture.