The heat capacity of a liquid is the amount of energy required to make 1cm3 of water rise by 1oC, and for water, the heat capacity is 4.2 joules per gram per degrees Centigrade.
Now that I have found a way in which to measure the variable that I will investigate, I must try to keep all of the other influential variables constant. These include the amount of water used in the beaker for heating; the distance between the burning alcohol and the beaker; and the position of the burning alcohol under the water, whether directly under the heating water or slightly off, it must be kept the same during all experiments.
Although I would have worked out the energy produced by the alcohol, I will not know how many moles this relates to, therefore I will have to work out the number of moles are in the 1cm3 of alcohol by using the following procedure for each type:
- Finding out the chemical formula,
e.g. Methanol – CH3OH
- Finding out the relative atomic mass or r.a.m for each element
e.g. Carbon (C) – 12
Hydrogen (H) – 1
Oxygen (O) - 16
- Working out the relative molecular mass or r.m.m
e.g. Methanol - CH3OH
(1x12) + (3x1) + 16 + 1
r.m.m = 32
-
Finding out the weight for each type of alcohol relative to 1cm3
e.g. Methanol – 0.791 grams
- Working out how many moles the alcohol contains
e.g. Methanol – 0.791g
32 r.m.m
= 0.025 moles
Now that I know the amount of alcohol produced and the number of moles in each alcohol, I can generate better, more reliable results and graphs; this is because the number of moles and the energy produced by the alcohol should, in theory, be directly proportional.
Preliminary Work
Before carrying out my actual investigation I had some time to plan out the procedure I was going to use by doing some pilot experiments. During these pilot experiments, I decided things such as, what size beaker I would use, how much alcohol I would burn, how much ceramic wool I would use, how much water I’d heat in the beaker and what distance the burning alcohol would be from the beaker of water.
Safety is a factor in all laboratory-based experiments; therefore this investigation was no exception. For the investigation, I wore suitable safety equipment; this was a) an apron, to protect my clothing and therefore some body protection and b) a pair of safety spectacles, to protect my eyes from any harmful substances or most importantly, flames.
Choosing all of the necessary equipment and deciding where and how to use each item was the next thing to do for my preliminary investigations.
Firstly, I chose a 100ml beaker to hold the water, which was going to be heated, in. This is because a beaker is the most practical container to use as it is small, easy to fill with water, easy to clean after each experiment, easy to measure the temperature of the water inside it and also has a reasonably large base. The large base of the beaker should cover as much of the flame as possible so as not to lose any of the heat given off from the burning alcohol. I also chose a beaker because not much of the heat can escape around it, therefore I will get more reliable results. To hold the beaker of water above the burning alcohol, I decided to use a boss and clamp and a retort stand; these would hold the beaker firmly above the crucible giving a smaller probability of an accident. It would also give the beaker better positioning so as to receive as much of the flame as possible from the burning alcohol below; this would therefore help me to obtain better results for my investigation.
Next I had to choose what to burn the alcohol in. As I was only burning approximately 1cm3 of alcohol, I decided to use a crucible. This is because a crucible can handle very high temperatures and is an ideal size for the experiment I am doing as it will not be sticking out around the beaker of water and therefore non of the heat will be lost.
As I had chosen to use a crucible, I needed to then find the amount of ceramic wool that would nicely cover the base of the crucible. I tried different amounts and I found that approximately 0.28 grams of ceramic wool was just right.
The next step was to choose what distance to put between the crucible and the beaker of water, but before I was able to do this I had to decide how much alcohol I was going to use and how much water I was going to put in the beaker for heating.
For the water, I first decided to use about 100cm3 but after doing one or two test runs, I discovered that it was too much water and that it didn’t heat up very much and therefore would not give very reliable results. I then decided to use 30cm3, which worked out just fine; any less would boil and any more wouldn’t heat up.
Taking measurements for the amount of alcohol (1cm3) and for my water (50cm3) would have to be very accurate for each and every experiment so that my investigation would be fair; therefore I would have to use correctly sized measuring cylinders for each measurement. I decided to use a small 10ml measuring cylinder to measure out my 1cm3 of alcohol, and a 25ml measuring cylinder to measure my 30cm3 of water. I will take my temperature measurements by keeping a thermometer in the beaker of water for the duration of the experiment; when the alcohol has stopped burning totally, I will quickly stir the water with the thermometer and take the final temperature before the water begins to cool down.
As I mentioned in my Output Variables, I have already decided to use 1cm3 of each type of alcohol; this was just the right amount as it didn’t produce as big a flame as 2cm3 of alcohol and therefore would not overheat the water.
Now that I had established how much alcohol and how much water I was going to use, I could start deciding what decided I would keep the crucible from the beaker. After a test run, I found that 2cm was a good distance, spanning from the top of the crucible to the base of the beaker. A larger distance would mean that not much heat would reach the water and would therefore give me unreliable results. A smaller distance would give the burning alcohol a small oxygen supply and therefore will not carry out complete combustion.
Now that I had decided on all of the equipment and volumes of the substances I was going to use, I carried out one final test run; this gave me a better idea on whether or not I had to change anything else before I started my investigation.
I carried out my test run, or ‘pilot’ experiment, using the following apparatus:
- Boss and Clamp
- Retort Stand
- Heat resistant mat
- Crucible
- 0.28g of Ceramic wool
-
Different types of alcohols (1cm3)
- Splints
- 100ml beaker
-
30cm3 of Water
- Bunsen burner
- Thermometer
- Electronic balance
- Safety Specs
- Apron
- Pipette
- 10ml Measuring Cylinder
- 25ml measuring cylinder
- Ruler
This is how the apparatus was set up:
I carried out the following procedure for each different type of alcohol and compiled some raw data. First, I fitted a boss and clamp to a retort stand to hold my beaker; then, I measured out 30ml of water in my 25ml measuring cylinder and poured it into the beaker and inserted a thermometer to start measuring a start temperature. Then I weighed 0.28 grams of ceramic wool and inserted it at the bottom of my crucible, which was placed on a heat resistant mat. I then measured out 1cm3 of an alcohol (e.g. Methanol), and poured it onto the ceramic wool in the crucible. Now that all of the apparatus was in place, I placed the top of the crucible two centimetres away from the base of the beaker and then I checked the start temperature and recorded it. The next stage was to light a splint by inserting it into a Bunsen burner, and then, set the alcohol in the crucible alight! After the alcohol had finished burning completely, I stirred the water and took an end temperature. Now that I had a start temperature and an end temperature, I could deduce the temperature rise and use it in the formula to work out the energy produced by the alcohol in Joules. The following are the results that I obtained from my preliminary work experiments.
As we can see from these results, the temperature rise is very high, there was not much of a range between the end temperatures, and so therefore I would need to change some of the set-up to make my investigation more reliable and fairer. In the case of Hexan-1-ol, there is no temperature rise because it boiled. Although there was no Pentan-1-ol to test, we can see that it would have had an end temperature of approximately 97oC. Therefore, to make my test fairer and more reliable, I must increase the distance between the top of the crucible and the base of the beaker, and increase the amount of water inside the beaker. This will insure that the temperature rise will not be too high and that the water will not boil.
I have therefore decided that for my investigation, I will change two things:
- The amount of water in the beaker to 50ml
- The distance between the top of the crucible and the base of the beaker to 2.5cm.
Background Knowledge
Hydrocarbons
In organic chemistry, hydrocarbons are a family of organic compounds composed entirely of carbon and hydrogen. They are the organic compounds of simplest composition and may be considered theoretically as the parent substances from which all other organic compounds are derived. The hydrocarbons are conveniently classified into two major groups, open chain and cyclic. In open-chain compounds containing more than one carbon atom, the carbon atoms are attached to each other to form an open chain; the chain may carry one or more side branches. In cyclic compounds the carbon atoms form one or more closed rings. The two major groups are subdivided according to chemical behaviour into saturated and unsaturated compounds.
Alkanes
The saturated open-chain hydrocarbons form a homologous series called the alkane, or paraffin, series. The composition of each of the members of the series corresponds to the formula CnH2n +2, where n is the number of carbon atoms in the molecule. Among the members of the series are methane, CH4; ethane, C2H6; propane, C3H8; and butane, C4H10. All the members of the series are unreactive; that is, they do not react readily at ordinary temperatures with such reagents as acids, alkalis, or oxidizers. The first four members of the series are gases at ordinary temperature and pressure; intermediate members are liquids; and the heavier members are semi-solids or solids. Petroleum contains a great variety of saturated hydrocarbons, and such petroleum products as petrol, heavy fuel oil, lubricating oils, petroleum jelly, and paraffin consist principally of mixtures of paraffin hydrocarbons, which range from the lighter liquid members to the solid members.
Alkenes
The alkene, or olefin, series of chain hydrocarbons are those in which a double bond exists between two carbon atoms. The general formula for the series is CnH2n, where n is the number of carbon atoms. As in the alkane series, the lower members are gases, intermediate compounds are liquids, and the higher members of the series are solids. The alkene series compounds are more active chemically than the saturated compounds. They easily react with substances such as halogens, adding atoms at the double bonds. They are found to some extent in natural products, and are produced in the destructive distillation of complex natural substances, such as coal, and are formed in large amounts in petroleum-refining, particularly in the “cracking” process. The first member of the series is ethene, C2H4. The dienes contain two double bonds between pairs of carbon atoms in the molecule. They are related to the complex hydrocarbons in natural rubber and are important in the manufacture of synthetic rubber and plastics; important members of this series are butadiene, C4H6; and isoprene (methylbuta-1, 3-diene), C5H8.
Alcohols
The term applied to members of a group of chemical compounds that contain the OH group. Also commonly used to refer to the specific compound ethyl alcohol, or ethanol. The word is derived from the Arabic al-kuhl, or kohl, a fine powder of antimony used as an eye makeup. The word alcohol originally denoted any fine powder, but the alchemists of medieval Europe later applied it to essences obtained by distillation, and this led to the current usage.
Alcohols have one, two, or three hydroxyl, -OH, groups attached to their molecules and are thus classified as monohydric, dihydric, or trihydric, respectively. Methanol and ethanol are monohydric alcohols. Alcohols are further classified as primary, secondary, or tertiary, according to whether one, two, or three other carbon atoms are bound to the carbon atom to which the hydroxyl group is bound. Alcohols are characterized by many common reactions, the most important of which is the reaction with acids to form substances called esters, which are analogous to inorganic salts. Alcohols are normal by-products of digestion and chemical processes within cells, and are found in the tissues and fluids of animals and plants.
Combustion
This is the process of rapid oxidation of a substance with simultaneous evolution of heat and, usually, light. In the case of common fuels, the process is one of chemical combination with atmospheric oxygen to produce as the principal products carbon dioxide, carbon monoxide, and water, together with products such as sulphur dioxide that may be generated by the minor constituents of the fuel. The term combustion, however, also embraces oxidation in the broad chemical sense, and the oxidizing agent may be nitric acid, certain perchlorates, or even chlorine or fluorine.
Hypothesis
The amount of energy released by the burning alcohol will be directly proportional to the number of carbon atoms in that specific alcohol.
Predictions
As the number of carbon atoms in the alcohol increases, so will the energy that it releases. I predict that they will be in direct proportion and therefore if one doubles, so will the other, and so on. As the number of carbon atoms in the alcohol defines the number of moles, along with other factors, the energy released by the alcohol will also be proportional to the number of moles in the alcohol.
Energy released
by the alcohol
Number of Carbon
atoms in the alcohol
Planned Method
Apparatus
- Boss and Clamp
- Retort Stand
- Heat resistant mat
- Crucible
- 0.28g of Ceramic wool
-
Different types of alcohols (1cm3)
- Splints
- 100ml beaker
-
50cm3 of Water
- Bunsen burner
- Thermometer
- Electronic balance
- Safety Specs
- Apron
- Pipette
- 10ml Measuring Cylinder
- 25ml measuring cylinder
- Ruler
Method
The method I will use to carry out my investigation is the exact method I used in my preliminary except for a few minor adjustments that I will make in my measurements. Instead of using 30cm3 of water as I did in my preliminary investigation, I have decided to use 50cm3, so as not to make the water boil. I also decided that the distance between the top of the crucible and the base of the beaker was too small, so I will change it to 2.5 centimetres for my investigation. Other than these two minor modifications in my set-up, the procedure I used in my preliminary work is the exact same procedure I will use in my investigation.
Obtaining Evidence
After carrying out my investigation using the exact procedure mentioned in the Preliminary Work and Planned Method, I compiled and processed the following data.
Repeats
Averages
Energy Produced
Analysing and Considering Evidence
Method
The method I mentioned in the planned method and preliminary work was the exact method I used in my final investigation; there were no further alterations to my set-up or procedure.
Conclusion
After carrying out my full investigation, obtaining my results, drawing out full tables of processed data and drawing one final conclusive graph, I have found that changing the number of carbon atoms in an alcohol will affect the energy that it produces when it is burnt. This is because more carbon atoms means a larger molecular structure and therefore more bonds within the molecule. Therefore if there are more carbon atoms reacting with the oxygen during combustion, there will be more carbon dioxide and water produced and therefore it will require a lot more energy to form bonds within these molecules. As shown in the results tables and the graph, the amount of energy produced by the alcohol and the number of carbon atoms within it was proportional and therefore nearly backs up my previous hypothesis. Except for the fact that in my hypothesis I stated that the number of carbon atoms in the alcohol and the amount of energy it would produce on burning would be directly proportional, not just proportional, and therefore my hypothesis would have been fully supported, had it been for the incomplete combustion of the Hexan-1-ol. Although some alcohols such as Hexan-1-ol required a larger oxygen supply than the other alcohols to undergo complete combustion and therefore did not produce the amount of energy it was meant to produce and therefore was expected to produce. The trend of the results and the graph show that the energy for Hexan-1-ol should have ideally been higher than it was to produce a nearly perfect set of results.
Evaluation
The evidence I obtained from my investigation was fairly reliable considering the fact that it was carried out in a school laboratory with limited resources. The procedures I used were also fairly adequate but could have been improved. There wasn’t much variation in the experiment, as the number of carbon atoms in each alcohol used didn’t have any range. There was also a lot of heat loss around the side of the beaker and from the top of the beaker, which could have been the cause of slight anomalies in my results. The only good point of the experiment was that every other variable except for the number of carbon atoms in the alcohols was kept constant. All of the apparatus allowed me to work to a very high degree of accuracy. The scales measured accurately to one hundredth of a gram, the measuring cylinders were accurate to the millilitre, the thermometer was accurate to the degree, and my ruler was accurate to the millimetre. Some of my results were slightly anomalous, especially the energy given off from the Hexan-1-ol. All of the anomalous results were highlighted in my results tables and clearly labelled on my graph. The only explanations I can give for the anomalies are incomplete combustion, heat loss, or human error (i.e. incorrect measurements of water, alcohol, distance between tip of crucible and base of beaker or temperature). The test was as fair as possible, and even if there were errors such as heat loss, they affected each and every experiment and therefore made hardly any effect on my results. The procedure I used was also reliable as the oxygen supply and heat loss were factors that again, affected each experiment and therefore didn’t have much of an effect on my results. There are, however, improvements that could be made to this experiment, such as using a conical flask instead of a beaker as it has a large base and would therefore intercept all of the heat of the flame produced from the burning alcohol and will therefore make the results more reliable. In addition, covering the top of the conical flask with foil and making a small hole for the thermometer would ensure that no heat could escape from the top of the conical flask. As a conical flask would be used instead of a beaker, there would be space for improvement, literally, as I could make the space between the base of the conical flask and the tip of the crucible larger so as to give the burning alcohol a larger oxygen supply. This would therefore allow every alcohol to undergo complete combustion and therefore make all of the results more reliable and the Hexan-1-ol in particular, would then fit into the trend.
I can finally come to a firm conclusion that, in theory, the number of carbon atoms in an alcohol and the energy that it releases when burned are directly proportional. The only extra work that can be carried out to provide additional information is by using that set-up and apparatus I mentioned above under how to improve the experiment.
