Physical Properties of Fatty Acids - Video Tutorials & Practice Problems
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Physical Properties of Fatty Acids Concept 1
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When it comes to the physical properties of fatty acids, we look at two things. It's determined by the carbon chain length and their number of pi bonds. Now, here, if we're taking a look at solubility in water, we're gonna say the length of the carbon chain is inversely proportional to solubility in water. Because remember as your carbon chain lengthens, you gain more carbons becoming more nonpolar and therefore you're less soluble in a polar solvent like water. So here we're going to say that as we increase our carbon chain length, we're gonna decrease the solubility in water. Remember, inversely proportional means they're opposites of each other. If one goes up, the other one has to come down. In this case, the longer your carbon chain becomes, the less soluble you become in water.
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Physical Properties of Fatty Acids Example 1
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In this example, it says which of the falling fatty acids would have the lowest solubility in water. I remember water itself represents a polar solve it. And we want the lowest solubility here. Remember there's an inverse relationship between the carbon chain length and its solubility in water. The longer your carbon chain length is the less soluble you'll be in water. So if we take a look here, we have different types of fatty acids and we're gonna say the this is 16 carbons, 18 carbons, 12 carbons and then 20 carbons. So here we're going to say the answer has to be option d this particular fatty acid because it possesses the most number of carbons. It's gonna have the longest carbon chain length which will result in the lowest solubility in a polar solid like water. So again, our final answer here will be option D. Here we have a acidic acid which has 20 carbons and no py bos.
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Physical Properties of Fatty Acids Concept 2
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In this video, we'll take a look at our second physical property of fatty acids melting point. Now, here we're going to say carbon chain length and the number of pi bonds have opposing effects on the melting point of fatty acids. Here, when we take a look at carbon chain length, we're gonna say that length is directly proportional a melting point. Meaning that if we increase our carbon chain length, then we're going to increase our melting point. If we take a look here at this graph, we have our temperature on the Y axis and number of carbons on our X. And we can see that as our number of carbons increases our temperature or melting point increases. Here we have 12 carbons, 16 carbons, 2024 carbons. Here, we have our loic acid. We have palmitic acid here. We have um eic acid and we have lido acid. And we can see as the number of carbon chain increases, the temperature is going up on the opposite side. We see the opposite occur here. We're going to say the number of pi bonds is inversely proportional. A melting point. Meaning that if I increase the number of pi bonds, I'm going to decrease my melting point. If we take a look here, we have asteric acid, which is well over 60 °C. In terms of temperature, just adding one pi bond to go to OIC acid causes a sharp decrease within our melting point. Lic acid here is somewhere around 11 to 13 degrees or so in terms of melting point. And if we add another pi bond, now we have two where we have linoleic acid, it's gonna go below zero °C in terms of melting point. So here we can see a great precipitous drop in our melting point as the number of pi bonds increases. So remember there is an opposite effect, increasing the carbon chain length increases my melting point, increasing the number of pie bonds decreases my melting point.
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Physical Properties of Fatty Acids Example 2
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Here in this example, question, it says within each pair determine the fatty acid with a greater melting point. Now remember if we increase our number of carbons, then that's gonna cause an increase in my melting point. And if I increase my number of pie bonds, that's gonna cause a decrease in my melting point. If we take a look here at our two fatty acids, we have STAIC acid with 18 folic acid with 18. So we can't rely on the number of carbons. What we rely on instead is the number of pie bonds. STAIC acid has zero pi bonds. Lic acid has one. Remember, increase the number of pi bonds decreases my melting point. So STAIC A would be higher in terms of melting point. Next, we have linoleic acid which has 18 carbons and three P bonds. And we have here met acid which is 23. So both of them have the same number of P bonds, but they have different number of carbons. Since this has more carbons, it'll have a higher melting point. Next, we have 18 carbons and one pie bond, 16 carbons and one pie bond. Again, the number of pi bonds are the same. But this one here has more carbon. So it's gonna have a higher melting point. And then finally, we have 18 carbons and four pi bonds, 20 carbons and three pi bonds. There's two forces at work here. First, our second fatty acid has more carbons which should result in a higher melting point. And in addition to this, it has fewer pi bonds, it has one less pi bond, which would also cause an increase in my melting point. So for those two reasons, this fatty acid would have a higher melting point. So these are the different fatty acids based on each pair that would have the greater melting point.
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