Alcohols are written with OH on the end as in CH OH (Methanol) or C H OH (Ethanol) or C H OH (Propanol) or C H OH (Butanol). The pattern of the carbon atoms creates a formula: C H with the OH on the end.
Once the energy has been calculated I will use the equation ‘ H =(E/ M)xMr’ to establish the heats of combustion.
Using these principals I would confidently predict that as the number of carbon atoms increases, the heats of combustion will also increase. This is directly due to the increase in Hydrogen atoms present.
Apparatus.
- Fire-proof mat
- Tripod
- Stand
- Clamp
-
200ml Pyrex™ beaker
- Tin can with 5mm perforations for air flow
- 4 Alcohols (Namely Methanol, Ethanol, Propanol and Butanol) in glass burners
- Splints
- Clasps
- Goggles
- Top-pan balance (Accurate to 3 decimal places)
- Thermometer + plastic clamp
Method
- Collect apparatus as described above and assemble like so:
- Place the first alcohol on the balance and record the weight.
- Measure out 100ml of water and pour it into the beaker.
- Note the starting temperature of the water.
- Place the burner under the can and ignite it.
- Monitor the temperature until it reaches the desired change and then extinguish the flame.
- Re-weigh the burner once it has cooled (handling it only with the clasps at first) and then deduce the change in weight.
- Repeat this for all 4 alcohol samples.
(To improve the efficiency of the experiment changes could be made such as using a heat shield or coating the inside of the tin with heat resistant paint. However I have chosen not to employ these methods because of practicality and lack of materials even though they would undoubtedly improve the accuracy of the experiment.)
Safety
- Basic lab safety precautions should be observed while conducting any experiment.
- When fire is involved special care is needed and all apparatus must be handled with caution and the correct equipment.
- As most of the equipment is metal then the heat will conduct throughout the apparatus and so all parts must be handled with caution.
- The alcohols are extremely flammable and so must also be handled with great care whilst any spillage must be cleaned up immediately.
- The glass beaker must also be handled with care, as rapid cooling by the introduction of cold water will shatter the container due to the severe heat change. Also if chipped the glass can cause gash wounds so caution is advised again.
- Excess water spillage can also create a hazardous working environment by making the floor slippery. Hence any spillage must, once again, be cleaned up immediately.
Repetitions
To improve the reliability of my experiment I would repeat all readings at least twice to eliminate any errors that might occur.
Results
These results will be calculated using the formula E=mc t to give the value of E and .
Errors
Certain errors comprising mainly of heat losses can be expected. However due to the small influence of these on the overall conclusions they can be ignored.
Conclusions and evaluations.
The results show that the heats of combustion are related to the number of carbon atoms in the molecule. The more carbon atoms there are the greater the heat produced. This is due to the increased presence of hydrogen atoms as there are more bonds to break. The breaking of bonds being the cause of the heat produced. Therefore the more bonds that are broken the more heat that is produced and the greater the heat of combustion will be. The gap between the samples grows greater each time and so it is fair to say that the increase between them is fairly significant as far as to say that I could logically predict the heat of combustion for the next alcohol in the series. The gradient of the graph re-enforces this, as it increases in gradient. The overall conclusions of this experiment agree with the facts laid down by the textbook Cambridge advanced sciences, Chemistry 1 and so can be assumed to be reasonably accurate. However the small errors that were made could be eliminated should the experiment be repeated. Errors such as the heat loss through the can. Introducing a heat shield or using a can made of a material with less heat conductivity could reduce this. If I were to require more accurate results I would conduct the experiment under such circumstances to give better results. However I think that the results I have obtained are sufficient to draw limited conclusions from and therefore are deemed adequate. However if I were to require more accurate conclusions more accurate results would need to be obtained form another experiment. Further experiments were not conducted due to lack of time.
Bibliography
Cambridge advanced sciences, Chemistry 1
Advanced science for you, Stanley Thornes
Mr Moore – A-level maths tutor
Numerous Internet sites.