1. Keep burner lit until the temperature of the water is 20°c higher and record.
1. Put out the spirit burner.
1. Weigh spirit burner again and record.
This is a crude method therefore we did some preliminary testing to find out where improvements can be made and to find out the optimal dimensions e.g. wick height and calorimeter height.
These are the amendments we made to get the best results by making the experiment more accurate:
∙ When measuring the amount of water to go in calorimeter I made sure that I measured it at room temperature and the surface of the water on the 200ml line not the sides as this gives a much more accurate measurement.
∙ When recording the temperature of the water I made sure that the thermometer was left in the water for some time before I took the recording so that it had time to adjust and therefore was more accurate.
∙ When handling the spirit burner I kept the lid on at all times (even when weighing) so that none of the fuel evaporated.
∙ When lighting the burner I will try to reduce the time that the lid is off and it is not lit by having a match already lit and having someone else to take of the lid and remove the draught shielding.
∙ The draught shielding should be sufficient in allowing enough oxygen in to ensure a clean and efficient burn and at the same time reducing the amount of draught, which can create inaccuracies.
∙ When heating up the water it is to be heated up to 2°c before the temperature difference is 20°c and the burner is put out so that it has time to get up to temperature as often it takes 2°c to get up to temp. This makes it more accurate as we are taking into account all the energy that is produced by the flame.
∙ When taking the temperature of the water I will use the thermometer to stir the water as well as taking the temperature, as this will make sure that the heat is evenly distributed and therefore it will insure that the test is as fair as possible.
∙ When it comes round to putting out the flame I will use the lid and not blow it out so that none of the fuel is lost to evaporation or anything. The lid will also be kept on until the weighing process.
∙ I will use a mercury thermometer as this is more accurate then an alcohol one and therefore will reduce the percentage errors.
∙ I will use the same equipment every time e.g. calorimeter, clamp, clamp stand, heat mat, thermometer. This is so that all the experiments are fair as different equipment is sometimes slightly off calibration so that at least if it is not greatly accurate it is relative so I can find a trend if there is one.
∙ I will use the same shape of spirit burner as this could make a difference to the burning and also I would like to use spirit burners with similar quantities of fuel left in them.
∙ I will also adjust the flame so it is the same height in each experiment as this could have an effect on how efficiently the fuel burns and could produce soot which is an insulator which would make my results inaccurate.
∙ Every time I repeat the experiment I will wait until all the equipment is back to room temperature so that none of the energy from previous attempts interferes with the current attempt.
As the experiment involves flammable and in some cases toxic or harmful chemicals there are safety issues that have to be emphasized. These have to be accompanied by common since and general lab behaviour.
∙ All participants have to be wearing goggles at the time of the experiment to protect their eyes.
∙ All long hair has to be tied back. This is especially important as we will be working with a naked flame and hair is flammable.
∙ When the flame is lit there should always be someone near to make sure it is ok. It should never be left unattended in case it gets knocked over or something.
∙ The lab should be well ventilated, as the carbon dioxide that is produced in combustion is unsafe to people if the concentration is too high.
Prediction
I predict that the more alcohols with the greater number of bonds will have the greatest combustion enthalpy change. My prediction is based upon the fact that they are all exothermic which means that more energy is lost in breaking the bonds of the reactants than is taken in by making the bonds of the products. In the combustion of alcohols, energy is given out at a higher ratio than it is taken in again by making the bonds, therefore the more bonds the higher the overall amount of energy given out.
Here is a balanced equation for the combustion of an alcohol in a surplus of oxygen:
CnOH + (n/2) O2 (n/3) CO2 + (2n/3) H2O
For Methanol this is:
C3OH + 1.5 O2 CO2 + 2 H2O
From this I can draw these diagrams to produce a simple way of working out the bonds that are broken and made:
Using the figures from data books as a reference and the number of bonds broken and made from my drawings I can show my prediction in these tables: