About thermal chemistry prac.

[Shashim]

Hi, I'm currently doing a prac report on thermal chemistry but I'm kinda lost.

Here is the procedure.
1. using a retort stand and clamp, set up a steel can 3-4cm above the wick of a spirit burner.
2. pour 200ml of water into the can and record its temperature.
3. Weigh the spirit burner and alcohol. Record the mass and the name of the alcohol.
4. light the burner and heat the water. Stir continuously
5. Once the water temperature has increased by about 20 degrees celsius extinguish the burner and record the highest temperature reached by the water.
6. measure the mass of the burner and hence deduce the mass of alcohol consumed. Record this mass.


The questions are:

1. what are the variables?? (independent, dependent, controlled)

Would independent be the type of alcohol used, dependent the change in mass and the temperature and controlled the volume of water??

2. When i did the calculations, the heat of combustion for each alcohol was very different to the theoretical values.

For example, for propan-1-ol, it comes out to be 10.13kj/mol when it should be about 2021 kj/mol.

The values i used were mass: 0.956g, change in temperature: 20.2



I would really appreciate it if anyone could help me with these problems.

THank you.