Which of these functional groups is soluble in aqueous HCl and/or NaOH?

Question

http://pastpapers.papacambridge.com/view.php?id=Cambridge%20International%20Examinations%20%28CIE%29/AS%20and%20A%20Level/Chemistry%20%289701%29/2015%20Jun/9701_s15_qp_42.pdf

I need some help to solve Q6 biii) of this paper, asking about which functional groups are present in E, F, G and H. I got the correct answers thinking that if something reacts with an acid or base, then it dissolves in them. But then I realized that amides and esters also react with both ( though heat is required, so that may be why they aren't said to be soluble ), and I also realized that in general my 'dissolves = reacts' notion is very flawed. So I discarded this concept, and tried to work on it fresh, but I am now very much stuck.

My approach before was this : Esters do not dissolve in cold aqueous bases or acids, nor do amides or alcohols. Amines dissolve in aqueous acids. Phenols and Carboxylic acids dissolve in aqueous bases.

From the molecular formula, we know that each compound contains either an Amine or an Amide functional group, so the rest of it is simply working out which combination fits which functional groups. Thanks!

Answer 1

Which of these functional groups is soluble in aqueous HCl and/or NaOH?

Functional groups don't have solubility. Their presence in a compound, however, can have an effect on solubility.

My approach before was this : Esters do not dissolve in cold aqueous bases or acids, nor do amides or alcohols. Amines dissolve in aqueous acids. Phenols and Carboxylic acids dissolve in aqueous bases.

That is the correct approach. Amines dissolve in aqueous acids because they are protonated to form a positively charged ion (unless other charged groups are present). Conversely, phenols and carboxylic acids are deprotonated to form phenolate and carboxylate anions.

From the molecular formula, we know that each compound contains either an Amine or an Amide functional group, so the rest of it is simply working out which combination fits which functional groups.

F and G are soluble in acidic solution, so they might contain an amine plus two oxygens from another functional group. The choices are carboxylic acid or ester, and the solubility in basic solutions shows that F has the former and G the latter.

E and H are insoluble in acidic solution, so they might contain an amide instead, plus one oxygen from another functional group. The choices are phenol and alcohol, and the solubility in basic solutions shows that H has the former and E the latter.