Like dissolves like

[danny89]

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Can someone check if my logic is correct: Methanol dissolves in water because both have hydrogen bonding (similar intermolecular forces dissolve with similar IMF or "like dissolves like"). But Pb(OH)_2 dissolves in HCl because its basic anion can easily dissolve in solutions of low pH. So these two concepts are mutually exclusive from one another?

 

[FeinMS]

Can someone check if my logic is correct: Methanol dissolves in water because both have hydrogen bonding (similar intermolecular forces dissolve with similar IMF or "like dissolves like"). But Pb(OH)_2 dissolves in HCl because its basic anion can easily dissolve in solutions of low pH. So these two concepts are mutually exclusive from one another?

First part sounds perfect. But the second part about Pb(OH)2 doesn't sound "like dissolve like" for me. Base is not like acid. The reason why Pb(OH)2 is more soluble in acid than base is because of complex eq.
Pb(OH)2 -> Pb2+ + 2OH-
In acid, OH- + H+ -> H2O.
This decrease [OH-], so pushes the first dissolving reaction to the right leading to more solubility.

Your logic is correct, but the only unclear thing is saying that base is like acid

 

[danny89]

First part sounds perfect. But the second part about Pb(OH)2 doesn't sound "like dissolve like" for me. Base is not like acid. The reason why Pb(OH)2 is more soluble in acid than base is because of complex eq.
Pb(OH)2 -> Pb2+ + 2OH-
In acid, OH- + H+ -> H2O.
This decrease [OH-], so pushes the first dissolving reaction to the right leading to more solubility.

Your logic is correct, but the only unclear thing is saying that base is like acid

Le Chattelier's principle. Got it.
Now, why is diethyl ether more soluble in CO2 than ionic (i.e. NaCl) compound's solubility with CO2? Is it because CO2 is nonpolar (zero dipole moment) and diethyl ether (both ethyls donate very little electron density to central Oxygen...very little polarity) is also nonpolar, thus, like dissolves like?
Also, are ionic compounds also included with polar compounds that dissolve in polar substances?

 

[FeinMS]

Le Chattelier's principle. Got it.
Now, why is diethyl ether more soluble in CO2 than ionic (i.e. NaCl) compound's solubility with CO2? Is it because CO2 is nonpolar (zero dipole moment) and diethyl ether (both ethyls donate very little electron density to central Oxygen...very little polarity) is also nonpolar, thus, like dissolves like?

CO2 is non polar, and in my opinion, diethyl ether is slightly polar, if not in the borderline. Therefore it will be more correct to say that diethyl ether is more soluble in CO2 than NaCl because it's less polar than NaCl.

 

[danny89]

Thanks 👍

 

[danny89]

Also, are ionic compounds also included with polar compounds that dissolve in polar substances? In #83 of general chemistry Self Assessment, it says that calcium sulfate has low solubility in water because both ions are highly charged and their attraction is too strong to break. However, I thought other ionic compounds, such as NaCl, dissolve really well in water. Thoughts on this?

 

[Pediateix]

so like dissolves like thing doesn't apply to acids/bases??

 

[aldol16]

Like dissolves like is a useful heuristic but heuristics shouldn't replace the role of critical thinking. Generally, "like dissolves like" comes from the fact that solutes have intermolecular interactions with other solute particles - in order for solvation to occur, the solvent must be able to replace those solute-solute interactions with powerful solute-solvent interactions (the solute-solvent interactions don't necessarily have to be as strong as the solute-solute interactions because there is also a favorable entropic factor arising from solvation). Here, you need to go back to those first principles - solute-solute interactions must be replaced with solute-solvent interactions. In this specific case, the relevant equilibrium is Pb(OH)2 <---> Pb + 2 OH-. The 2 OH- will interact strongly with H+ in acid solutions. So much so, in fact, that they will react to form H2O. This removes OH- from the solution and therefore drives the dissolution equilibrium to the right. The H+'s present in the solvating solution allows for interactions with OH- that drive dissolution.