kaplan question on solubility. PLEASE HELP!

[RHC1987]

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Possible explanations for the low solubility of acetylene in H2O include:

• acetylene interferes with hydrogen bonding between H2O molecules
• intermolecular attraction between acetylene and water is weak
• acetylene does not readily form hydrogen bonds

I and III only
II and III only
I and II only
I, II, and III <---ANSWER

I had a question about the first roman numeral... Im having a hard time understanding why its true! I thought that a solute is solvable when the interaction between solute and solvent is greater than that between solvent-sovent molecules... so if it interfered, wouldn't it be more soluble?? and also, acetylene is nonpolar and water is polar.. so why would it interfere with H-bonding?? WHYYYY???

 

[RPedigo]

Possible explanations for the low solubility of acetylene in H2O include:

• acetylene interferes with hydrogen bonding between H2O molecules
• intermolecular attraction between acetylene and water is weak
• acetylene does not readily form hydrogen bonds

I and III only
II and III only
I and II only
I, II, and III <---ANSWER

I had a question about the first roman numeral... Im having a hard time understanding why its true! I thought that a solute is solvable when the interaction between solute and solvent is greater than that between solvent-sovent molecules... so if it interfered, wouldn't it be more soluble?? and also, acetylene is nonpolar and water is polar.. so why would it interfere with H-bonding?? WHYYYY???

You kinda answered your own question without knowing it. You have the concept down, it just didn't click.

The acetylene interferes with the hydrogen bonding because it blocks close approach of two water molecules. This disrupts hydrogen bonding because if there are two water molecules that could H-bond and you put an acetylene in between them, you just disrupted it. Water doesn't like that. You just broke up it's H-bonding and offered it nothing in return (as you said, acetylene can't H-bond with water).

There isn't much solute-solvent attraction as you said, so solubility is low. Water just says eh, move along, and the acetylene doesn't dissolve because there is no energetic reason for it to do so. It's basically like trying to dissolve oil.

 

[RHC1987]

haha! ahh brilliant! thanks~ the pictures really helped 🙂