This is a flammable colourless chemical compound with a formula C2H5OH.
It is widely used in alcoholic drinks and alcohol thermometers. It has a density of 0.789 g/cm³ a boiling point of 78.4 °C (351.6 K) and a melting point of
The aim of this experiment is to find out the composition of 3 unknown liquid mixtures of ethanol and water substances using the method of Gas Chromatography.
a) GAS CHROMATOGRAPH:
PYE UNICAM 204 CHROMATOGRAPH
DETECTOR: Thermal Conductivity
COLUMN: Ropak Q
COLUMN TEMP: 180ºC
DETECTOR TEMP: 250ºC
INJECTOR TEMP: 250ºC
INJECTION SIZE: 2.0μl
COMPUTER INTEGRATOR: ATI UNICAM 4880 DATA HANDLING SYSYTEM
b) 5.0 μl syringe
- Switch on the chromatograph and the integrator for some time before actually commencing the practical. This is to allow the machine to be ready for the introduction of the sample.
- You will be provided with:
10% ethanol / 90% water (w/W)
30% ethanol / 70% water (w/W)
50% ethanol / 70% water (w/W)
70% ethanol / 70% water (w/W)
90% ethanol / 10% water (w/W)
- Introduce about 2μl of each of the liquid that is to be analysed into the 5μl syringe
- Inject the sample into the front injection part located on the front left hand side of the chromatograph. You may experience some magnetic resistance while inserting the syringe.
- Push down the plunger to release the liquid into the chromatograph. Keep the syringe in the hole for at least 3 seconds so as to achieve full vaporization
- After removing the syringe, press the inject button on the data capture unit which is below the screen monitor
- The chromatogram of the liquid will be displayed on the computer screen
- The integrator will stop collecting data and print the results after a few minutes from the time of injection.
- The integrator resets itself and the ready button lights up. This indicates that it is ready to take in the next sample.
- Repeat for all the compositions, printing off after each one.
- Now carry out same tests on the three samples of liquid A, B and C.
Experiment should be carried out away from any source of ignition.
HAZARD AND RISK ANALYSIS
The COSHH and MSDS sheets for this experiment are attached to this report.
Table showing the ethanol peak area and water peak area for the known samples.
Table showing the ethanol peak area and water peak area for the unknown samples.
A graph of ethanol peak area against ethanol concentration is attached to this report.
DISCUSSION AND INTERPRETATION
A plot of ethanol peak area against ethanol concentration yielded a straight line graph which contained three anomalies at 10%, 50% and 90% ethanol concentration. The anomalies could have occurred as a result of errors that could have happened during the experiment. A major source of error discovered during the experiment was the presence of bubbles in the syringe when the volumes of the samples were being measured. This affects the accuracy of the chromatograph readings.
Also, the syringe might not have been properly cleaned after each sample was taken and this would affect the purity of the next sample.
From the values obtained during the experiment for the ethanol peak areas obtained during the experiment for samples A, B and C and from the graph drawn for the known ethanol concentrations, I found the concentration of ethanol for the samples.
This experiment can be improved by using a higher range of ethanol concentrations and obtaining more readings for each of the known samples and the unknowns and finding an average for the peak areas. This would improve the accuracy of the readings and thus improve the overall experiment.
Bubbles in the syringe could be minimised by taking extra care when measuring out the samples. A larger syringe could possibly be used.
Gas Chromatography Handout Given by J.P Fletcher
Appendix A- Microsoft word processor used
Microsoft excel used for coshh data