In the following pairs of compounds, which would you expect to...

Question

In the following pairs of compounds, which would you expect to be more soluble in water? Why?

a. C₈H₁₇COOH or CH₃CH₂CH₂COOH

Accepted Answer

All right. Hi, everyone. So this question is asking us is the following statement correct because C six H 13 C double oh has a larger hydrocarbon part. Then C three C two C double oh C six H 13 C double oh is more soluble in water than CH three ch two C double oh. Option A says the statement is correct and option B says the statement is incorrect. Now, just for the record here, this the question is having us compare Hepton OIC acid which is C six H 13 C double oh versus propionic acid or C three sorry ch three CH two C double oh But before we get into their structural differences, I wanna talk about polarity and how that contributes to solubility in certain solvents. Because recalled polarity is the main principle that distinguishes what salutes will dissolve in certain salutes, right? Recall that the phrase like dissolves like exists for this very reason, right? It discusses the fact that sos of similar polarity to the solvent will dissolve. But the question then becomes what is polarity, right? How can you tell whether or not a substance is polar or not? Well, to determine this. When examining the structure of a certain compound, you would consider whether or not that compound has at least one dipole moment. And if there's multiple dile moments, the idea is to ensure that those dile moments do not cancel out. So recall that a dipole moment discusses a difference in electronegativity between two atoms that are bound together. So when we consider the structure of water, for example, water exhibits a dipole moment because oxygen is more electron than hydrogen. And we can discuss specific electron negativity values too. Oxygen has an electron negativity of 3.5 where hydrogen has an electron negativity of 2.1. So if we consider this difference, right, if we examine the difference in electronegativity between oxygen and hydrogen, we can see that that difference is 1.4. That's the difference in the electron negativity values of these two atoms. Now because the difference here of 1.4 is greater than 0.4 then this means the bond between oxygen and hydrogen is therefore going to be polar, right? There is a dipole moment. So because there's a dipole moment, right, the dipole moment is going to point towards oxygen because oxygen is more electron and considering the fact that there are two dipole moments pointing towards oxygen, this explains why water is polar, right? We have multiple Dapo moments but they do not cancel out. So now that we've discussed why exactly water is polar, we can therefore confirm that polar solus will dissolve in water and not nonpolar solid. So it's at this point that we can begin to compare the structures of Hepton OIC acid versus propionic acid. So Hepton OIC acid is a carboxylic acid that has a six carbon chain attached to the car bono carbon, right. So I have my carboxylic acid group at the very end of the chain and the remaining six carbons are simply an ocho group. And by contrast, propionic acid is three carbons in total, meaning that there is a two carbon alko group attached to the carboxylic acid. Now, what's worth pointing out here when examining the structures of both carboxylic acids is that both of them have polar regions and both of them are capable of hydrogen bonding, right? Because there is an electron negativity difference in the bonds between carbon, the carboxylic acid carbon and both oxygens they're attached to. So they both have a polar region because the carboxylic acid group is polar and both of them are capable of hydrogen bonding. Because notice how carboxylic acids have hydrogens that are attached to highly electron atoms, specifically oxygen. However, we cannot just examine the polar region of the compound in isolation, right? Because recall that this hydrocarbon part, this hydrocarbon chain is going to affect its overall solubility in water. Recall that carbon carbon bonds and carbon hydrogen bonds are considered to be nonpolar because there's a smaller difference in electronegativity between these atoms. So the larger the hydrocarbon part is in a molecule like a carboxylic acid, right. The larger the non polar region of the compound is going to be right. And that affects the overall solubility in a polar substance like water. So considering the fact that Hepton OIC acid has a much larger hydrocarbon chain than propionic acid. Hepton OIC acid will actually be less soluble in water than probiotic acid. And the reason for this is because the hydrocarbon chain is nonpolar whereas the carboxylic acid group is polar. So even though there is a polar region in this compound in Hepton OIC acid, the non polar region is larger because there are more carbon, carbon and carbon hydrogen bonds. So therefore, that is going to affect the overall solubility, meaning that Hepton OIC acid is going to dissolve or is going to be less soluble in water compared to probiotic acid. So because of this, we can see that the statement provided is actually incorrect. So our answer is going to be option B in the multiple choice tanic acid is actually less soluble in water. And so with that being said, thank you so very much for watching. And I hope you found this helpful.

In the following pairs of compounds, which would you expect to be more soluble in water? Why?
a. C₈H₁₇COOH or CH₃CH₂CH₂COOH

Key Concepts

Hydrophilicity vs. Hydrophobicity

Carboxylic Acids and Solubility

Chain Length and Solubility

Watch next