Propanamide and methyl acetate have about the same molar mass,...

Question

Propanamide and methyl acetate have about the same molar mass, both are quite soluble in water, and yet the boiling point of propanamide is 213 °C, whereas that of methyl acetate is 57 °C. Explain.

Accepted Answer

All right. Hi, everyone. So this question says that ethyl acetate and butter amide have similar molar masses and are both soluble in water. However, the boiling point of ethyl acetate is 77.1 °C. While butter amide has a boiling point of 216 °C provide a reason for the difference in boiling points. Butter amide has a higher boiling point than ethyl acetate because a it has more electron atoms b it is nonpolar C it can form a hydrogen bonds with itself or d it has more carbons. So if I scroll down here for a second, notice how I went ahead and I drew the structures of ethyl acetate and Beter Aide for comparison. And the reason why I felt it was important to have the structures on hand is because recall of the boiling point is a consequence of what intermolecular forces or IMF s the molecules have. Now recall that intermolecular forces are forces of attraction that compel molecules of a certain substance to remain close together. So during the boiling process, these intermolecular forces have to be broken so that molecules can flow freely as a gas So it makes sense to say that if the intermolecular forces holding a molecule together or multiple molecules together are stronger, then the bulling point or BP is going to increase, right, because more energy is required to break a stronger intermolecular force. Now recall that there are several types of intermolecular forces that can be determined by examining the structure of a given compound. The strongest of which is the ion dipole interaction in which an ion interacts with a polar covalent compound. Now, the second strongest is going to be hydrogen bonding or h bonding. And you can tell that a molecule is capable of h bonding if you have a hydrogen atom connected to a highly electron atom. Now, the most common electron atoms that you can see a hydrogen attached to are nitrogen oxygen and fluoride. The third strongest is the dile dile interaction in which two polar covalent compounds interact with each other. And the weakest are known as dispersion forces. Now, all molecules are capable of dispersion forces, but it is the primary IMF exhibited by nonpolar compounds and it is actually the weakest. Now, if I consider the structure of ethyl acetate, first, right, notice how we have one carbon atom connecting to two oxygen atoms. Now, oxygen is more electron than carbon, which means that there is going to be a dipole in these two carbon oxygen bonds. And so in this case, right, the dipole moment would point towards both oxygen atoms meaning they do not cancel out. So because the structure of ethyl acetate proves that there is a net dipole ethyl acetate is polar. And because ethyl acetate is polar, it is capable of dipole dipole interactions. Now, the same can be said for butter amide, right, because butter amide also has a carbon oxygen and a carbon nitrogen bond, both of which would have a dipole moment. However, notice how butter amide has an NH two group and hydrogen here is connected to an electron atom, specifically nitrogen. And this means that butter amide is capable of hydrogen bonding whereas ethyl acetate is not. And so this explains the main difference that we saw in the boiling points of these two compounds because each bonding which be a mind is capable of is a much stronger intermolecular force than the dipole interactions that ethyl acetate can exhibit. So because butter amide has a stronger intermolecular force, it has a much higher boiling point than ethyl acetate. Now, just for the record, because the question did mention molar mass recall that molar mass can only affect the dispersion forces, right. So the the discussion of the molar mass only matters when comparing the intermolecular forces of nonpolar substances. But in this case, they're both polar and on that note, right, because both compounds are polar, they are both going to dissolve in water because water is also polar. So if I scroll back up here to consider my answer choices. Then my answer is going to be option c in the multiple choice, right? Butter amide has a higher boiling point than ethyl acetate because it can form hydrogen bonds with itself. And so with that being said, thank you so very much for watching and I hope you found this helpful.

Propanamide and methyl acetate have about the same molar mass, both are quite soluble in water, and yet the boiling point of propanamide is 213 °C, whereas that of methyl acetate is 57 °C. Explain.

Key Concepts

Intermolecular Forces

Hydrogen Bonding

Molar Mass vs. Boiling Point

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