- Set up the apparatus for reflux distillation.
- Boil the mixture gently using a water-bath for about half an hour.
- Cool the apparatus dismantle and rearrange for distillation.
- Distil off about 15 cm3. This is aqueous ethanoic acid.
Purification
The mixture is put into the round bottomed flask along with a few anti-bumping granules, and the fractionating column is fitted into the top.
As the mixture boils, vapor rises up the column. The vapor condenses on the glass platform inside the column, and runs back down into the liquid below.
The column is heated from the bottom. The vapor at the top of the column then passes into the condenser, which cools it down until it liquefies. The condensate that was initially very close to the azeotrope composition becomes gradually richer in water. The process continues until all the ethanol boils out of the mixture. This point can be recognized by the sharp rise in temperature shown on the thermometer.
Fractional Distillation
The distillation process is used to separate the impurities in the solution. Ethanol had a boiling point of about 78oc and the ethanoic acid had a boiling point of about 118oc. The distillation technique separates the solutions and hopefully leaves it with no impurities.
When the temperature reaches the boiling point of the different substances in the solution each part is fractionally distillated. To collect the different fractions we collected them in different test tubes. When the temperature got to specific points we changed the test tube to collect the different fraction that boils at that specific temperature.
Testing Impurities
Universal indicator
We used universal indicator to determine the pH value of the different fractions. Ethanol had a boiling point of 78oc and this fraction was a pale green and yellow colour. This shows that it has a pH value of 4. The other fraction that was collected boiled at 118oc and this was the ethanoic acid. This had a pH value of 3.
Potassium Dichromate
I added 1cm3 of my solution to 5 drops of potassium dichromate and 5 drops of sulphuric acid into a test tube and I heated it in a hot water bath for 10 – 20 minutes. After it was finished reacting, the colour of the solution was green and this tells me that the solution that I made was impure.
Purpose of Refluxing
A reflux system is used to condense vapours escaping from the hot flask. After about 20 - 30 minutes of refluxing over a water bath, it can be assumed that the reaction is complete.
Here is the balanced equation for the reaction I have carried out.
The molar mass for ethanoic acid is:
CH3COOH
C = 2 x 12 = 24
H = 4 x 1 = 4
O = 2 x 16 = 32
Molar mass = 24 + 4 + 32 = 60
Measurement errors
There are many different measurement errors that could have occurred.
Some of the main measurement errors are the amount of ethanol and dilute sulfuric acid wasn‘t exact. To minimize this make sure that you are eye level with the measuring cylinder and the little dip in the liquid sits on the amount that you want.
Observations
Purification
During the purification, while I was heating the aqueous ethanoic acid it started to evaporate and it left a brown substance around the pear shaped flask.
Conclusion
After doing this experiment I concluded that I did produce some ethanoic acid. To make this experiment better if I was going to do it again I would make sure that I have measured out everything accurately and carefully.
During the fractional distillation, I only collected two different fractions so this tells me that maybe my measurement were incorrect. I will also make sure that I will measure out accurately every measurement that there is and try my best to make sure that they are as accurate as possible.
Evaluation
We only managed to produce very little ethanoic acid. To try and improve this experiment, if I was to do it again, we could have checked all my equipment before we used it to make sure that there wasn’t any other substance that could have contaminated my results. Also, I would repeat the same experiment more than 3 times so this will enable me to get an average from the different results and this will give me a more precise result.
