- The wick of the alcohol burner. This needs to be kept constant because the flame will be bigger and hotter is there is a longer wick, or smaller and less hot if the wick is short. Obviously this would affect the rate of temperature increase of the water because a bigger hotter flame is more likely to heat up the water faster than a smaller less hot flame. I will keep this constant by measuring the length of the wick each time I do an experiment.
The Variable I will change
- The alcohols. I will change the alcohols each time and investigate how much mass is lost in the heating process in each case. I will take a mass measurement before heating the water, and after heating the water, subtract one from the other to get the difference or mass lost. This lose in mass will show me how each of the alcohols affect the temperature increase in the water differently and also show me how much energy is released.
2 Wooden Blocks
Spirit Burners (Methanol, Ethanol, Propanol, Butanol, Pentanol)
Pour distilled water from a glass beaker through a funnel into a burette and fill a copper tin with 150ml of water.
Place a thermometer into the can of water and leave it there while you measure and record the initial mass of your chosen spirit burner.
Make sure the wick of the spirit burner is pulled out to a length of 1cm.
Place the spirit burner on top of 2-stacked wooden blocks underneath the tripod stand and place the copper can on the tripod stand. Record the temperature of the water.
Remove the cap of the spirit burner and using a lighted splint, light the spirit burner and stir the water with the thermometer being careful not to touch it against the bottom of the tin, which is hotter than the water and would affect your results.
Once the temperature of the water has gone up 15 degrees, place the cap back on the spirit burner. Remove the cap after a few seconds and wipe away any condensation that had formed in it.
Placed the spirit burner back on the scale and record the final temperature of the water.
For my preliminary work, I will decide on how much water to use and how much of a temperature increase I will allow before extinguishing the flame of the spirit burner. This needs to be established because the burner has to burn for long enough to make a significant weight decrease in itself so that the scale can measure accurately.
I will use Pentanol in this preliminary investigation because it has the most carbon atoms and will therefore give out the greatest amount of heat. This is important because less of it will burn to increase the temperature of the water to a given amount, and therefore a small mass decrease will occur. I must establish a suitable volume of water that will take long enough to raise the given amount of degrees and that will cause a substantial weight loss.
Using my results from my preliminary results, I have decided that I will use 150ml of distilled water because any thing less heats up to fast and will not give accurate results. Any thing more than 150ml is unnecessary because it takes a long time to heat up and is a waste of time.
I will heat the water up 15 °C because 10 °C doesn’t take very long to heat up and won’t give me reliable results.
To ensure accurate results, I will use more precise measuring instruments such as a burette instead of a measuring cylinder. I will also use a digital top pan balance that measures to 100th of a gram, which is very, very accurate.
To ensure that my results are reliable, I will do three repeats of each of the 5 alcohols, which are 15 sets of results in total. Doing repeats will allow me to spot any anomalous results very quickly and easily.
Safety goggles must be worn at all time. Careful attention must be taken to not inhale any of the fumes from the alcohols as this may cause dizziness.
Hypothesis and Prediction
I predict that as the alcohols move up from Methanol to Pentanol, and gain a carbon atom each time, the energy released per mole will increase consecutively as you move up from Methanol to Pentanol. The longer the hydrocarbons in the chain of alcohols, the more heat it will produce. As the number of carbon atoms present in an alcohol increase, the energy released when the alcohol is burnt will increase too.
My hypothesis is that Methanol will release less energy per mole than Ethanol, Ethanol less than Propanol, Propanol less than Butanol, Butanol less than Pentanol. Pentanol will therefore release the most amount of energy per mole.
Analysis and Conclusion
My results prove that as the alcohols descended down the group (Methanol – Pentanol) the mass loss decreased. This means that more energy was released as the number of carbon atoms increased as we descend down the group.
I can conclude that my hypothesis was correct; methanol did release the least amount of energy per mole than any of the other alcohols. Methanol released less than Ethanol, Ethanol less than Propanol, Propanol less than Butanol, Butanol less than Pentanol. Pentanol release the most amount of energy per mole.
My method was good. I don’t believe that there would have been any inaccuracies caused by the way I carried out my investigation however, my trend was weak, so there must have been a weak spot in my method.
Some heat could have been lost to the surroundings, so if I were to do the experiment again, I would insult it so no heat would be lost to the surroundings.
The can could still have retained heat from the previous experiment, even though I tried to cool it down. If I was to do the experiment again, I would use more than one can, and alternate them to make sure that the cans were properly cooled before I used them again.
I could have left the thermometer on the bottom of the can for too long instead of stirring the water with it. This would lead to inaccuracies because the thermometer would measure the temperature of the bottom of the can, which would be higher than the temperature of the water.