Problem 7. Problem 8. Problem 9. Problem Video Transcript Samir asked. Draw the condensed structural formula for a fatty acid and identify it as sa…. Explain why oleic acid 18 carbons, one cis bond has a lower melting poi…. Explain why the melting points of the saturated fatty acids increase as we m….
The melting points of a series of 18 -carbon fatty acids are: stearic acid, …. Predict which acid in each pair has the higher melting point and explain why…. Which molecule woul…. They can observe the melting and freezing points of the acid and can plot a graph.
This experiment could also be done using data-logging equipment. This practical takes quite a long time to carry out. Students can begin by simply recording their data but, once they get the hang of what they are doing, most should be able to plot the graph at the same time as taking readings. If data-loggers are being used then students will need another activity to be doing alongside the experiment. Remind students not to attempt to move the thermometer in the solid stearic acid, as it will break.
Energy must be supplied to melt a solid; this same energy is released when the liquid re-solidifies. This presents a good opportunity to demonstrate how to maintain a steady temperature using a Bunsen burner. This can be achieved by sliding the Bunsen burner aside as the boiling becomes too vigorous; slide it back as the water stops boiling. It is not essential that the water bath is boiling. A temperature sensor attached to a computer can be used in place of a thermometer.
It can plot the temperature change on a graph and show this as it occurs. A slight modification of the experiment can yield an intriguing result: When the test tube is cooling place it in an insulated cup containing a few cm 3 of water.
Use a second temperature sensor to monitor the temperature of the water. The water temperature should rise as the stearic acid cools and it should continue to rise even as it changes state. A slight alternative to this experiment is to plot only the cooling curve.
Place all the boiling tubes with stearic acid into a large beaker. For example, stearic has a melting point of 69 o C whereas palmitic acid has 63 o C.
Stearic acid is a C 18 fatty acid and palmitic acid is C 16 fatty acid. Both are saturated fatty acids but stearic acid C 18 has more molecular weight than palmitic acid C 16 hence more melting point.
Molecular weight increases with number of carbons and hence chain length of the fatty acid. Therefore C 18 fatty acids will have more molecular weight than C 16 fatty acids. As the chain length increases, the Van der Waals forces between fatty acid molecules increases thereby intermolecular forces increase. As a result, the melting points are much lower for unsaturated fatty acids. Amal Mears Professional. What affects melting point of fatty acids? Will definitely affect melting point , as this website explains pretty well: " Melting point principle: as the molecular weight increases, the melting point increases.
Mencey Gemeinert Explainer. Is stearic acid saturated or unsaturated? Stearic acid is a typical long chain saturated fatty acid. Oleic acid is a typical monounsaturated fatty acid. Linoleic acid is a typical polyunsaturated fatty acid. Jonatas Panasco Explainer. What is the formula of fatty acid? Fatty acids are long chain carboxylic acids, they contain the carboxyl, COOH, functional group.
If the hydrocarbon chain, R, contains only single bonds between the carbon atoms, the fatty acid is said to be saturated. Miles Likov Explainer. Which lipid is most soluble in water?
Phospholipids have both a polar, hydrophilic end, and a nonpolar, hydrophobic end. Phospholipids are partially soluble in water, meaning that part of the molecule is attracted to water, and part of it is not. Daiana Sonder Pundit. What is the melting point of arachidic acid? Arachidic Acid Properties. Alfredo Bendezu Pundit. What is palmitic acid used for? Palmitic acid is used to produce soaps, cosmetics, and industrial mold release agents.
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