An experiment to find the heat energy in different alcohols.

Apparatus

· Beaker

· Thermometer

· Measuring cylinder

· Weight scales

· Gauze

· Tripod

. 6 different alcohols

. Wood block

. Heat mat

. Matches

The method that I will use is as follows:

· Measure 100ml of water into a beaker.

· Record the starting temperature of the water.

· Weigh the alcohol

· put the chosen alcohol under the beaker allowing the flame to just touch bottom of the beaker.

· Leave to heat up until the temperature rises by 20oC.

· Weigh alcohol again.

The variables that I must keep the same are:

· Mass of the water 100ml

· Temperature rise of 20°C.

· the height of the alcohol from the beaker.

· Same temperature start

The variable that I will change is:

· The type of alcohol used.

Prediction

I predict that the more bonds there are holding the carbon, oxygen and hydrogen atoms together, the more heat energy will be needed to break them apart. For example Ethanol has five C-H bonds, one C-C bond, one C-O bond and one O-H bond. To break these types of bonds you will need a certain amount of heat energy. To brake a C-H bond you need to give out around 410 joules of energy. All of the other alcohols can be broken up in this way. Which means the longer molecule takes more energy to break its bonds. I can come to predict that the longer the molecular atom in the alcohol the more energy it will take to break the bonds. So this means I can predict that Butanol will need more heat energy than methanol because it has more bonds to break.

Results

Alcohol

Starting temp (c)

Finishing temp (c)

Weight loss

Methanol

20

40

2.808

Ethanol

20

40

2.102

Propanol

20

40

2.726*

Butanol

20

40

.372

Pentanol

20

40

2.784*

Hexonal

20

40

.591

*Repeated

Alcohol

Starting temp (c)

Finishing temp (c)

Weight loss

Propanol

20

40

.863

Pentanol

20

40

.416

This is a table showing the number of carbon atoms in the different alcohols:

Alcohols

Number of carbon atoms

Methanol

Ethanol

2

Propanol

3

Butanol

4

Pentanol

5

Hexanol

6

Analysing and drawing conclusions

I think my results tables and graphs clearly show the pattern that I have found in this experiment. That is that heat combustion increases when the amount of carbon atoms increases. I believe that my results show that the more carbon atoms there are the heat of combustion grows. These results support my prediction. After this I can conclude that my prediction was right but I didn't find out all of the experimental problems. I conclude that carbon atoms in alcohols have an effect on the heat of combustion. As the amount of carbon atoms go up the heat of combustion goes up as well. This is because every time you add another carbon atom you add more on to the mass.

Evaluation

Light energy and some heat energy could have been lost in the surroundings. I could have put heatproof mats around my experiment to prevent heat loss but some heat would still be lost. The beaker that the water was in would have used up some of the heat energy to heat up first before the water. The alcohol containers had different amounts of alcohol in them to start with along with different sizes of wicks. This all adds to the fact that the flame coming from the alcohol was different in size as well so sometimes it might not even be touching the beaker. The room temperature would also cool down things. This was a difficult experiment to do in a classroom because there are lots of different ways of losing heat because everything likes to gain heat energy. If the oxygen supply is low then you get some atoms of carbon let out before they can bond with any oxygen atoms. This creates what we call soot. To prevent this I could make sure there is a proper oxygen supply