Repetition
The experiment will be repeated with each fuel at least 3 times because this will provide a range of results allowing me to identify anomalies and calculate a mean
Control of variables
Treatment of results
The results that will be gathered will be tabulated.
Convert the volume of water to a mass by using the known density of water (1000 cm3 = 1000 gram). An average will be calculated making sure anomalies are left out. Then a calculation of the enthalpy change of combustion will be calculated using the formula. These will then be compared with the text book enthalpy change of combustion figures that have been obtained from Royal Society of Chemistry Electronic Databook 2002.
Methanol = CH3OH, the enthalpy change of combustion = -726.0 kJ mol-1.
Ethanol = CH3CH2OH, the enthalpy change of combustion = -1367.3 kJ mol-1
Propan-1-ol = CH3CH2CH2OH, the enthalpy change of combustion =
-2021.0 kJ mol-1
Butan-1-ol = CH3(CH2)2CH2OH, the enthalpy change of combustion =
-2675 kJ mol-1
Limitations
The same equipment will be used for each experiment. The only things that will be changed are the two different types of fuels, along with the spirit burners that contain them.
The room temperature cannot be changed easily. The room temperature is not significant to the outcome of the results. The starting temperature of the water is more important. The experiments could all be done on the same day to reduce temperature errors.
The loss fuel cannot be stopped totally so when doing the experiment it is best to put the lids on the burners when they are not lit and measuring the mass of the burners as soon as they have finished heating the water. Doing this will help increase the accuracy of the results.
Prediction
It is predicted that the longer the hydrocarbon chain the more energy will be transferred to the water therefore fewer moles of fuel will be used to achieve the same temperature rise.
The rationale for the prediction is based on working out the bond breaking and bond forming energies for each reaction.
Firstly methanol
CH3OH + 1 ½ O2 --> CO2 + 2H2O
Bond Breaking energy
Bond Making Energy
Therefore for Methanol ΔHc = +2808-3466 kJmol-1
ΔHc = -658 kJmol-1
For Butan-1-ol
C4H9OH + 6O2 --> 4CO2 + 5H2O
Bond Breaking Energies
Bond Forming Energies
Therefore for Butan-1-ol ΔHc = +7874-11080 kJmol-1
ΔHc = -3206 kJmol-1
The calculations here are different to the textbook values and their differences will be explained in the analysis later on.
Precautions
Safety is very important because the fuels are highly flammable and one is toxic so eye protection must be worn at all times. Make sure that if either alcohol becomes ignited that you cover with a heatproof mat to starve it of oxygen. When using the top pan balance to measure the weight of the burner the calculation needs to have a reading of up to 2 decimal places so the top pan balance needs to be checked first. When moving equipment make sure that it is moved slowly and carefully as broken equipment can cause damage. More importantly is not to move the top pan balance as it could change the readings. Simple things like no sitting down and hair being tied back has to be taken into account as well.
Hazards
Each fuel has different hazards, which need to be identified. Using the Major hazard card (Cleapss 1995) it is possible to identify these hazards.
Methanol and Ethanol (Hazard card number 40) are highly flammable and will catch fire at temperatures above 13oC and they are dangerous with bromine, mercury and silver nitrate, platinum and potassium. However propan-1-ol and butan-1-ol (hazard card number 84) are more reactive and are also highly flammable and can catch fire at 21oC. They are harmful if inhaled and can cause irritation if spilt on skin. They are dangerous with oxidising agents and keytones, as they will react vigorously. Below are some key points of what to do in the specified situation. These points apply to all four fuels.
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If the vapour is inhaled then the victim must be removed to fresh air.
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If the liquid is splashed in the eyes, the specific eye must have running tap water over it for 10 minutes, whilst someone seeks medical attention.
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If spilt onto clothes or skin, then remove the contaminated clothing and wash the affected area
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If spilt tin the laboratory then shut off all sources of ignition, open all windows and apply a mineral absorbent to the spill, then scoop into a bucket and add water
Preliminary Results
Preliminary work will be done to find out the problems that could occur and how they can be fixed. Preliminary work was obtained from the salter activity sheet DFI.2. During the preliminary work only one fuels will be tested. Methanol will be tested, as this is more volatile. Finding out where to hold the thermometer and where to stir in the calorimeter will also be achieved. Along with the distance of the flame to the calorimeter. This is important because it will reduce energy loss if the space between the calorimeter and the burner is narrowed.
Making sure that the variables are within a measurable range will also be checked. By using 200cm3 of water it can be found out if it is too much or too little. Timing the experiment will also be done to see if the temperature rises to quickly so that the results cannot be taken down, or if it rises too slowly so that it takes to long to do 5 experiments for each fuel. The results of the preliminary work will be analysed and if it necessary the method could be changed.
References
- Cambridge Press, Chemistry textbook
- Royal Society of Chemistry, Electronic Databook 2002
- Hazard Card (number 40 and 84), Cleapss 1995
- Salters Advanced Chemistry 200
