I have to try and make sure the place where I take the experiment is more or less the same. This is because if I sat near the window for one experiment and didn’t for the other experiment it will not be a fair test.
There are certain variables that I need to control to make sure that the experiment is carried out in a fair way:
Mass of water
Length of wick on burner
Type of alcohol
Height of can above flame
Type of can
Prediction
I predict that when the alcohol has more carbon atoms the moles needed to increase the water temperature will decrease.
Time of burning
To actually find out what the heat evolved is, I must use the following formula: Heat Evolved = Mass x Specific Heat x Temperature Rise.
Apparatus
Beret
Distilled water
Tissue paper to clean the bottom of the tin
Tin
Thermometer
Tripod
Alcohol’s
Stand to stand the beret
Blocks of wood to put the alcohol’s on
Weighing machine
Method
I will first get the alcohol burner that I will use to heat up the water. The burner will be weighed this will be recorded. Then either with a beret or weighing the water I will get 150ml of distilled water. Then under the tripod I will put the blocks of wood. I will then measure the wick trying to be as accurate to 1cm as possible. Then I will heat the water and stir the water with a thermometer. I will heat the water and heat it for 10ºc. Then I will put the cap on. After I have cleaned the cap with tissue paper I weigh the alcohol burner and record the results. I do this twice for each alcohol.
Fair test
To make it a fair test I will have to:
- Try and clean the soot at the bottom of the alcohol burner to prevent unequal combustion. We can see if there is unequal combustion if the flame it yellow instead of blue. The alcohol has not burnt properly therefore carbon and carbon monoxide are given off instead of oxygen.
- I will try and stir the water at a constant speed as this will alter the results.
- The length of the wick has always got to be the same as this will alter the height of the flame.
- I will have to clean the cap of the alcohol burner after the flame is extinguished as there will be soot and condensation on the cap which will make the weight of the alcohol burner heavier.
The results that I obtained are below.
Analysis
I predicted that when the alcohol has more carbon atoms the moles needed to increase the water temperature will decrease. When the alcohol has more carbon atoms the moles needed to heat the water by 10ºc will decrease. This is what I have to find out:
· Energy evolved
· Energy per gram
· Energy per mole
Energy evolved = Mass x Rise in temperature x SHC
Energy evolved = 150g x 10ºC x 4.2
Energy per gram of fuel = Energy evolved x Mass of fuel burnt
My prediction seems to be incorrect this may be because my results were inaccurate. I thought as the energy decreases the molecules increase.
The explanation is :
If more energy is needed to make a bond than to break a bond energy is given out, this is heat. This is an exothermic reaction. When you have two carbon bonds there are four C=0 bonds but if there are four carbon bonds there are eight C=O bonds.
Evaluation
My final results that I achieved were extremely inaccurate. Although I cleaned the bottoms of the tins there was still a yellow flame proving there was incomplete combustion. The alcohol has not burnt properly therefore carbon and carbon monoxide are given off instead of oxygen.
A limited amount of oxygen means we get carbon monoxide and each carbon atom can only bond with one oxygen atom. Limited oxygen means that some carbon atoms are released before they can bond with oxygen which creates soot.
I tried to make sure the wick always kept the same height but it was very difficult to get it right with a ruler. Although the thermometers were accurate to half a degree, I still made mistakes either putting the cap on too early or too late. We had to try and make sure when we were measuring with a beret that the marker was eye level but as the beret is so high up it was difficult.
The tins were not good insulators therefore letting heat out everywhere so it took longer for the water to heat up. There was no lid on the tin so that meant there was heat loss form the top of the tin.
I may have improved my results by using other alcohols making a bigger range, I could have used hexanol or heptanol. As my graph was not good this could have improved it and make more of a curve. I could have maybe used bubble wrap and have a lid on the tin. The bubble wrap is a good insulator that wouldn’t let as much heat out giving a much better result. If we used a new tin every time this would prevent incomplete combustion therefore being more accurate. The flame was aimed at the centre this means it would be the centre of the tin would get heated the most making it unfair. We could have used a long tube or a burner which covered more area.
