Mass of alcohol burnt for a temperature rise of about 10i?? c. This is a sensible rise of water temperature because it is large enough to measure changes in the mass of alcohol burnt but small enough that it won’t take too long to do each one. I will investigate how the type of alcohol affects the mass needed to create a temperature rise of about 10i?? c in water. Hypothesis I predict that as you go up the series of alcohols e. g. from methanol to ethanol etc. less alcohol will have to be burnt for the temperature rise of about 10i?? c in the water.
I believe this because of the results of my preliminary work (below) which shows that the amount of energy given off any alcohol is directly proportional to the size of the molecule. Here is a sketch graph of what I expect to happen: Safety Safety goggles should be worn at all times Keep clothing away from the flame Keep Bunsen flame on the safety flame when not using it Apparatus Tin can 300ml measuring cylinder Clamp stand and boss 8x spirit burners (one for each alcohol) Diagram of apparatus can containing water x x x x x=clamps Heat (from spirit burner)
Controlled variables-fair test To make the investigation fair I will ensure that as many variables as I can remain the same: Liquid used Amount of liquid (400ml) Can used Length of wick penetrating the top of the spirit burner Distance of can above flame Starting temperature of water Ensure there are no drafts from open windows to blow the flame However, there are also uncontrollable variables such as: room temperature and soot on the bottom of the can etc. Preliminary Work 1 I carried out preliminary trial runs to test the suitability of my plan.
I used three alcohols: The smallest in the range of alcohols I have been given (methanol), the middle of the range (propanol), and the largest in my range (octanol). These are my results: Methanol: Weight difference: 1. 20g Temperature difference: 10. 50 degrees Celsius Propanol: Weight difference: 1. 20g Temperature difference: 13. 50 degrees Celsius Octanol: Weight difference: 0. 79g Temperature difference: 10. 50 degrees Celsius I found no problems with the experiment so am not change anything for the real thing. Final method For each experiment, 400ml of water will be measured with a measuring cylinder and put into a can.
Measurements will be taken at the level of the top of the water to reduce parallax error. I will weight for the water to become room temperature. The mass of the spirit burner before heating will be weighed. I will leave the cap on (explained later). The can will be suspended on in the middle of the flame to ensure that as much of the available heats goes into the water that is possible. The alcohol will be lit quickly to ensure that heat from the Bunsen flame does not transfer to the water and affect the readings. I will stir the water with a thermometer all the time to ensure and even temperature (no spots of high temperature).
I will wait for the temperature to rise by about 10i?? c and extinguish the flame quickly with the cap. The cap will remain on the spirit burner to stop smoke from being lost (reason for leaving cap on in first weighing). The mass of the spirit burner after heating will be recorded. This will be carried out three times for each alcohol and an average will be calculated. Anomalous results will be repeated. This will increase accuracy. Preliminary Work 2 I was able to work out the amount of energy that should be released by each alcohol by firstly working out the energy required for bond breaking.