like dissolves like - covalent solvent better for covalent solutes than ionic?

[GomerPyle]

How do covalent solvents have preference of covalent compounds rather than ionic, since covalent can mean both polar or nonpolar? I encountered a question in self assessment where it states that covalent solutions prefer covalent compounds rather than ionic compounds due to "like dissolves like", but I thought that only applied to properties such as polarity or charge, not covalent vs ionic since covalent can also be polar (or semi-charged)?

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[The Kraken]

Without an actual example it will be tough to tell exactly what you mean.

 

[ToldYouSo]

A polar solvent will dissolve an ionic solid, and a nonpolar solvent will dissolve a nonpolar compound.

Water, hexane, ethanol, acetone are all covalent liquids with varying polarities. The like dissolves like phrase refers to solvents that are either polar or nonpolar, *not* ionic vs covalent, because there are very few ionic liquids; the only one I can think of off the top of my head is molten NaCl.

 

[sakabato93]

How do covalent solvents have preference of covalent compounds rather than ionic, since covalent can mean both polar or nonpolar? I encountered a question in self assessment where it states that covalent solutions prefer covalent compounds rather than ionic compounds due to "like dissolves like", but I thought that only applied to properties such as polarity or charge, not covalent vs ionic since covalent can also be polar (or semi-charged)?

What kind of self-assessments are you doing?

The like-dissolves-like refers to nonpolar vs polar, not covalent vs. ionic.

 

[GomerPyle]

Sorry for not being clear guys. Chem self assessment (aamc) number 68.

Which of the following compounds are soluble in supercritical CO2?

NaCl
C2H5OC2H5
NH4NO3
KOH

In the passage, it states that "For a supercritical fluid, the density and ability to dissolve other substances are similar to values expected of liquids." I am assuming this refers to a liquids property of "like dissolves like".

Now, the answer is diethyl ether. The explanation is "According to the principle of like dissolves like", the covalent compound CO2 is a better solvent for a covalent compound than it is for an ionic compound. Diethyl ether is a covalent compound, whereas all other options are ionic.

So this is what sparked my question. I thought "like dissolves like" only pertains to polar/charge properties where polar substances dissolve in polar solvents, and vice versa. I didn't think that "like dissolves like" applies to covalent and ionic character as well since covalent bonds can be both nonpolar and polar. It doesn't make sense to me...

 

[FeinMS]

I would really appreciate if you can post your self assessment questions on the thread for self assessment. Every time i look at your thread, i see a spoiler. I know i cant tell you what to do but i wish you can be nicer to ppl whi havent taken the self assessment thanks

 

[ToldYouSo]

Sorry for not being clear guys. Chem self assessment (aamc) number 68.

Which of the following compounds are soluble in supercritical CO2?

NaCl
C2H5OC2H5
NH4NO3
KOH

In the passage, it states that "For a supercritical fluid, the density and ability to dissolve other substances are similar to values expected of liquids." I am assuming this refers to a liquids property of "like dissolves like".

Now, the answer is diethyl ether. The explanation is "According to the principle of like dissolves like", the covalent compound CO2 is a better solvent for a covalent compound than it is for an ionic compound. Diethyl ether is a covalent compound, whereas all other options are ionic.

So this is what sparked my question. I thought "like dissolves like" only pertains to polar/charge properties where polar substances dissolve in polar solvents, and vice versa. I didn't think that "like dissolves like" applies to covalent and ionic character as well since covalent bonds can be both nonpolar and polar. It doesn't make sense to me...

Try not to get too hung up on the terminology. CO2 and diethyl ether are both nonpolar compounds. It's the polar/nonpolar distinction that's important, not ionic/covalent.

 

[sakabato93]

Try not to get too hung up on the terminology. CO2 and diethyl ether are both nonpolar compounds. It's the polar/nonpolar distinction that's important, not ionic/covalent.

Diethyl ether is a polar compound, but because it has very low polarity, its considered a nonpolar solvent. Don't mean to cherry-pick, but this is an important distinction.

 

[The_Sunny_Doc]

Diethyl ether is a polar compound, but because it has very low polarity, its considered a nonpolar solvent. Don't mean to cherry-pick, but this is an important distinction.

It is an important distinction for orgo. Ether can dissolve most organic compounds because it can be a hydrogen bond acceptor (unlike a hydrocarbon) even if it can't hydrogen bond with itself.

Gomerpyle, maybe it'd help to think of how dissolution goes towards what's energetically favorable. It's more energetically favorable for the nonpolar molecules to stay together van der Waaling each other than to try to mingle. It isn't energetically favorable for them to venture out and try to break apart charged molecules. They're happier just hanging out with each other.

Try to picture polarity as a gradient, with your ions waaay over to the polar side on the right, and the covalent compounds which have some polarity in the middle of the spectrum. Symmetrical alkanes would be to the far left. No partial charge at all on them except temporarily.

 

[sakabato93]

It is an important distinction for orgo. Ether can dissolve most organic compounds because it can be a hydrogen bond acceptor (unlike a hydrocarbon) even if it can't hydrogen bond with itself.

Gomerpyle, maybe it'd help to think of how dissolution goes towards what's energetically favorable. It's more energetically favorable for the nonpolar molecules to stay together van der Waaling each other than to try to mingle. It isn't energetically favorable for them to venture out and try to break apart charged molecules. They're happier just hanging out with each other.

Try to picture polarity as a gradient, with your ions waaay over to the polar side on the right, and the covalent compounds which have some polarity in the middle of the spectrum. Symmetrical alkanes would be to the far left. No partial charge at all on them except temporarily.

+1👍

 

[ToldYouSo]

Diethyl ether is a polar compound, but because it has very low polarity, its considered a nonpolar solvent. Don't mean to cherry-pick, but this is an important distinction.

It is an important distinction for orgo.

This is the MCAT. For all intents and purposes it's a non-polar compound. Technically, hexane, heptane and cyclopentane are polar but in the orgo lab setting it's always described as a nonpolar solvent.

 

[sakabato93]

This is the MCAT. For all intents and purposes it's a non-polar compound. Technically, hexane, heptane and cyclopentane are polar but in the orgo lab setting it's always described as a nonpolar solvent.

But understanding that diethyl ether has an nonzero net dipole moment is a very important concept for gen chem. It acts as a nonpolar solvent for orgo purposes, but if you were to analyze an ether compound for polarity for the PS section, it would definitely have a polarity.

I'm not sure why you say hexane, heptane, and cyclopentane are "technically" polar? If you're talking about induced dipoles/london dispersion, then its completely different than with ethers.