Investigating how much energy is produced when burning alcohols.

Apparatus

To perform the experiment, the following apparatus must be used:

• Clamp
• Measuring cylinder

• Matches

• Metal beaker
• Alcohols
• Safety goggles
• Heatproof mat
• Electronic scales

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Jack Mariner                                                     Chemistry Coursework 2

Safety Precautions

Although this experiment is very simple, safety must always be taken into account. Firstly, heat is being applied so you must lay a heatproof mat out protecting the surface below. Also goggles must be worn to protect the eyes just in case of unexpected explosions or in case something is to spit up into ones face during the experiment. Alcohol is flammable and must be used with extreme care. 

Method 

First we got our equipment out and set it up as shown in diagram 1. We took the metal beaker and measured 100ml of water into it using a measuring cylinder. We recorded the water temperature, which was identical to the room temperature. Amazingly, throughout our experiment this temperature did not change

Then we weighed spirit burner so as to make a comparison with its final mass. We fixed the water in place with the clamp and put the spirit burner directly underneath it. We then lit the string at the top of the burner with a match.

With a thermometer we stirred the water whilst regularly checking its temperature. When the temperature had risen by 25C we took the burner to the electronic scales and ascertained its new mass. This mass could now be compared with the original mass. This was done for each of the five alcohols.  

The variables that must remain constant throughout the experiment are…

        · Mass of the water 100cm

        · Type of beaker, metal

        · Temperature rise of 25°C.

        · The height of the beaker from the wick

        · Same set of scales

        · Weigh the spirit burner with the lid on.

Fair Test

There are many things that can be done to keep this experiment a fair one. Firstly the same metal beaker must be used as all of them have different circumferences. The amount that the temperature raises must be the same otherwise incorrect results would be obtained leading to anomalous. You must measure the amount of water you put in to the metal beaker in all 5 cases so that the time in which the spirit burner is alight is of a fair standard. The height of the beaker from the wick is also

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Jack Mariner                                                     Chemistry Coursework 2

an essential factor of a fair test. If the beaker is nearer then it would change the results completely.

Errors will be kept to a minimum with the use of digital weighing equipment.

Results

Table 1

Graph 1

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Jack Mariner                                                     Chemistry Coursework 2

Immediately from the results we can establish that each of the alcohols did infact lose mass while conducting the experiment. This is due to energy being transferred in heating and lost in the atmosphere.

From these results we can work out the total energy given out per mole for each alcohol.

Methanol- CH3OH

Energy given out= mass of water x   SHC   x temperature change

        (Joules)               (100g)                 (4.2)                    (25)

=        10,500J

So if 1.61g of methanol gives 10,500J

Then 1g of methanol (32g) gives:  

10500

61. X 32  =208KJ

So for methanol the total amount of energy given out per mole is 208KJ.

Ethanol- C2H5OH

So if 1.40g of ethanol gives 10,500J

Then 1g of ethanol (46g) gives:  

10500

40. x 46  = 345KJ

So for ethanol the total amount of energy given out per mole is 345KJ.

Propanol- C3H7OH

So if 0.75g of propanol gives 10,500J

Then 1g of propanol (60g) gives:

10500

75. x  60  =  840KJ

So for Propanol the total amount of energy given out per mole is 840KJ.

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Jack Mariner                                                     Chemistry Coursework 2

Butanol- C4H9OH

So if 0.88g of Butanol gives 10,500 J

Then 1g of butanol (74g) gives:

10500

88. x  74  =  883KJ (to 3 s.f)

So for Butanol the total amount of energy given out per mole is 883KJ.

Pentanol- C5H11OH

So if 2.95g of pentanol gives 10,500 J

Then 1g of pentanol (88g) gives:

10500

95. x  88  =  313KJ (to 3 s.f)

So for Pentanol the total amount of energy given out per mole is 313KJ.

Below is a table with the amounts of energy given out per mole, for each alcohol:

Table 2

These theoretical results were obtained from a Chemistry data book written by B. Earl and L.D.R. Wilford.

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Jack Mariner                                                     Chemistry Coursework 2

Graph 2

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Jack Mariner                                                     Chemistry Coursework 2

Analysing the results

From the graph you can clearly establish that anomalous results have occurred. I predicted that Pentanol would have the highest amount of energy given out per mole, when infact it had one of the lowest! I don't think that this is because I got it wrong, what has happened is that one of my results is wrong. The mass of the spirit burner containing Pentanol was incorrect for either before or after doing the experiment. This meant that the temperature change was huge compared to what it probably should have been. From studying my other results I would expect that the change in mass for Pentanol would be about 50g to 65g. This is because the results appear to be declining as the amount of atoms increases, and 50 to 65g is an appropriate suggestion for the change in mass, given this information.

This is supported by my graph on the previous page. The line of best fit has a positive gradient, and goes past the points accurately. The graph also shows that my results for Pentanol were anomalous results. The point drawn on the graph for this is obviously out of place. I would expect it to be in the region of about 900-1000KJ.

From studying 'Table 1' I can establish that my results are similar to those obtained by another group. The results obtained from experimenting with Methanol, Ethanol and Propanol were extremely similar but those from Butanol and Pentanol varied a bit. My results showed that the change in mass for Propanol was less then that from Butanol. The compared results were quite the contrary. I believe that my results are the incorrect results if any. This is because, like stated before, the more atoms there are the less the change in mass will be. Propanol has more atoms then Butanol but my results show Butanol to have a higher change in mass. Like the compared groups results, I would expect for Propanol to have a higher change in mass then Propanol.

For Pentanol, although the change in mass that I obtained was more than twice as much as that of the compared result, they are both surprisingly similar. The similarity is that both are more then they should be. They are both obviously to high, meaning that they are both anomalous results. I think this phenomenon happened either by coincidence or because the alcohol used was contaminated. This could lead to such results.

Now because the results obtained with Pentanol were anomalous results, it is very likely for the amount of energy per mole to be wrong. That was the case.  In my hypothesis I stated that 'as the amount of atoms in the alcohols increase, so will the amount of energy per mole.'

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Jack Mariner                                                     Chemistry Coursework 2

As you can see from 'table 2' my hypothesis is correct. If you look at the theoretical results, you will see that my hypothesis is proved to be correct because as the amount of atoms increases, so does the amount of energy per mole. Methanol, having the least amount of atoms, has the least amount of energy per mole. This is the case not only in the theoretical but also in my results and the compared results.

I was unable to find the theoretical values of Pentanol but it is still clear that both the compared results and mine are incorrect. Going by the theoretical results they should be about 3000J to 3500J. You can see though that my results are only a small percentage of the theoretical values. This is because of draughts and heat and energy lost to the atmosphere. Taking this into account I would expect that the amount of energy per mole for Pentanol be about 1500J.

Evaluation

I consider this experiment to be a success. The plan was followed very well and the results were of good quality. The measurements were done accurately, and a fair test was achieved. The procedure used was also a very fair and efficient one.

Although the experiment was a success, I am still bothered by the fact that anomalous results occured in my experiment. I think that the reasons for these results were because of time limitations and careless mistakes. We had very little time to accomplish this task successfully, so mistakes were inevitable.

 

The improvements, which could be made in doing this experiment, are to have a longer time to do the experiment so that isn’t done making careless mistake and if mistakes were made, there would be enough time to redo what was needed. Secondly more high tech equipment could be used to get more reliable and accurate results.

        

Conclusion

From 'table 2', you can see that my hypothesis is of high quality stating that 'as the amount of atoms in the alcohols increase, so will the amount of energy per mole'. This was a perfect prediction.

Thus for my conclusion, I conclude that

'As the amount of atoms in the alcohol increases, so does the total amount of energy per mole.'

This is the case in my results excluding any anomalous ones. Which is why this wasn't reflected as strongly as it should've been.