Lauric Acid Lab Report

Lloyd

Term 2, 2014

Lauric Acid Experiment

Teacher: Mr Oliver

Contents

1.0 Introduction
Elements and the compounds can exist in distinctive physical states. Liquid, solid, gas and plasma. Every element and compound has a distinctive melting and boiling point. When a substance reaches its melting and boiling point it will change phase. For example the molecules in a solid being heated gain energy and eventually are able to not only vibrate but rotate. This means the molecules have now changed phase to a liquid. Lauric acid is a fatty acid that exists as a solid at room temperature. It has a melting and freezing point of 43.20Celsius. The molecular structure of lauric acid is C12H24O2.
(Chemical Book, 2012). Because of the relatively low melting point it is suitable for use in laboratory experiments. Pure substances have a boiling/melting point that is unique to them and a way to test their pureness is to plot a cooling curve on a graph. If a substance is pure a horizontal line will appear when the substance is changing phase. (Refer to graph Part A which clearly shows the horizontal line.) (Nave, 2014) Stated that the line is horizontal when a substance is changing phase because the energy being put in or taken away isn’t making the substance hotter or colder it is instead changing the state of the substance.
2.0 Aim
The aim of the experiment is to investigate the freezing and melting behaviour of a compound
3.0 Hypothesis
The hypothesis of the experiment is that liquid lauric acid will begin to freeze at the same temperature that solid liquid lauric acid begins to melt. The temperature of the lauric acid between the time it takes to change phase will remain constant
4.0 Justification
The hypothesis will be justified by a graph showing that the melting and freezing curve of the lauric will intersect and plateau at the same temperature. The temperature will remain constant when the lauric acid is changing phase because the energy being put or taken away is not changing the temperature but changing the state.
5.0 Materials
Safety glasses
2 400ml beakers
2 thermometers
1 large test tube
2 wire gauzes
2 utility clamps
2 gas burners
2 ring stands
2 rig supports
1 copper wire stirrer
1 rubber stopper
Lauric acid
20cm copper wire
Beaker tongs or insulated glove

6.0 Variables
Independent- Temperature of the water bath
Dependent- Temperature of the lauric acid
Control- Set up of the experiment and volume of lauric acid

7.0 Results
Part A heating

Part B Cooling

8.0 Analysis Questions

Using the data from Part A, determine the melting point of lauric acid.
From the data collected in Part A it can be determined that lauric acid melts at 470 Celsius. Does the temperature of a substance vary while it is melting or freezing? Explain It can be inferred from the data collected that the temperature of a substance varies while it is melting and freezing. The results collected show this because both graph Part A and Part B have a gradient.
Using the data from Part B, determine the freezing point of lauric acid. From the data collected in Part B it can be determined that lauric acid freezes at 400 Celsius.
Does lauric acid melt and freeze at the same temperature? According to the results lauric acid does not freeze and melt at the same temperature.
Explain the shape of the curves in terms of the energy changes that are occurring in the sample as it heats up and melts and as it cools down and freezes. The curves of the graph relate to the phases the lauric acid is going through. At the start of graph Part A the line is increasing. The energy being put into the lauric acid is directly changing the temperature of the acid. After two minutes however the line goes horizontal. This is the part of the graph where the energy being put into the acid is not changing the temperature but changing the phase. In Graph Part A this is from a solid to a
liquid.
Explain how an increase in the amount of lauric acid used would affect the shape of the curve.
An increase of lauric acid would mean that the curves of the graph would be have less gradient because a greater volume of lauric acid would take a longer period of time to change phase. The horizontal section of section of the graph would also be longer because more energy would be required for the lauric acid to change from a liquid to a solid and solid to a liquid.
Explain in your own words what is going on at the molecular level as liquid lauric acid cools and freeze. As liquid lauric acid cools and eventually freezes the molecules of lauric acid are losing their heat to the surrounding water bath. When the lauric acid molecules eventually lose enough heat energy the attractive forces between them pulls them together and they form a crystalline structure. The molecules are unable to move because they do not have enough energy to break away from the solid lauric
acid.

9.0 Discussion
The results collected do not support the stated hypothesis. The lauric acid did not melt and freeze at the same temperature. This can be seen in the graphs from Part A and Part B. The horizontal section of graph Part A showed that lauric acid melts at 470Celsius. The horizontal section of graph Part B showed that lauric acid freezes at 400Celsius. The second part of the hypothesis was supported by the results. The temperature of the lauric acid did vary less while it was changing phase. Part A graph has a horizontal section where the lauric acid was melting. The horizontal line not only showed the melting point but supported the knowledge that a pure substance plotted on a cooling curve graph will have a horizontal line where it changes state. Possible reasons why the lauric acid did not melt and freeze at the same temperature include; misreading of the thermometer, misinterpreting the results and not using an accurate method of recording the temperature. Ways of improving the method of the experiment include; using an electronic thermometer which would reduce human error and conducting multiple trials and taking the average.
10.0 Conclusion
The experiment conducted showed that lauric acid does not freeze and melt at the same temperature. The experiment did however show that the lauric acid used in the experiment was pure because a horizontal line was produced when it melted and froze. A horizontal line was produced when the lauric acid was melting because the energy being put in was not changing the temperature of the acid but instead changing the state. Errors made in the experiment include misreading of the thermometer and misinterpreting the graphs. Improvements that could be made to the experiment are the use of an electronic thermometer and multiple trials.

Bibliography
Chemical Book. (2012). Retrieved June 12, 2014, from http://www.chemicalbook.com/ChemicalProductProperty_EN_CB0357278.htm
Nave, R. (2014). Georgia State University. Retrieved 6 12, 2014, from Hyperphysics : http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/heatra.html#c1