Solubility

[victorias]

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A chemical compound is insoluble in water. Upon reaction with NaOH, however, the compound becomes soluble. What has most likely happened to the chemical compound?

A
An -O- group or a -COO- group has been protonated
B
An -OH or a -COOH group has been ionized
C
A hydrogen from an alkyl group has been lost to OH- to make H2O and a water soluble carbanion
D
A hydrogen from an alkyl group has been lost to OH- to make H2O and a water soluble carbocation

The answer is B.

But isn't -OH or a -COOH group already soluble? The question stem states that the we are starting with something that is insoluble and by reacting with NaOH, it is becoming soluble.

Here is my thinking process

A. NaOH disssociates into Na+ and OH- so it can't protonate something
B. -OH or a -COOH group already soluble - The question stem states that the we are starting with something that is insoluble and by reacting with NaOH, it is becoming soluble. This was my basis for eliminating this answer choice
C. Losing a H+ from alkyl group would make a carbanion which could be soluble in water, and starting with an alkyl group, it meets the criteria of starting with something that is insoluble
D. Carbocation is not made by losing H+

 

[aldol16]

But isn't -OH or a -COOH group already soluble? The question stem states that the we are starting with something that is insoluble and by reacting with NaOH, it is becoming soluble.

Not necessarily. Think about fatty acids.

C. Losing a H+ from alkyl group would make a carbanion which could be soluble in water, and starting with an alkyl group, it meets the criteria of starting with something that is insoluble

Carbanions are not stable and will not exist in solution. That's assuming sodium hydroxide can deprotonate them, which it cannot unless it's the alpha carbon to a ketone. The pKa of a plain alkyl group is simply too high.