First off, it's great to see you understand all these concepts and how to calculate pH! But that for the most part is irrelevant to the question.
Just as a side thing, lines given don't mean you have to fill them all out or write twice as much; it's a good indicator of how much you should be writing. The fact that you've gone and written up a whole page of mathematical calculations should ring a few warning bells (ie. it's all well and good, but am I doing something wrong here?). In addition, you're missing the key word in explain. You can calculate the pH like your life depends on it, but if you don't answer the question you could only get a maximum of 1 with maximum leniency. Most times, you'd get zero because you haven't answered the question. The while part of the question is also pretty important as it indicates that you need a comparison of some sort, but that's basically covered in the explain part.
What you need to be doing is writing two key equations:
HCl
(aq)→H
+(aq)+Cl
-(aq)CH
3COOH
(aq)⇌CH
3COO
-(aq)+H
+(aq)Note that the second equation uses an equilibrium arrow, while the first doesn't. Here you can also throw in your K
a values if you a) want to be super fancy or b) somehow remember them or c) both, but it's not completely necessary. Relate these two things if you have them, otherwise relate the equations to the strength of dissociation in water. Say that HCl is a strong acid, and (for our purposes) dissolves completely in water (ie. 1 mol L
-1 of HCl will produce an equal amount of hydrogen ions, and then by subbing into the pH equation, gives you that pH of zero.) In contrast, acetic acid doesn't dissociate completely as a weak acid, and will not produce 1 mol of hydrogen ions, thus resulting in a corresponding higher pH. The hole here is the 2.6, but you can do the math if you really want to and prove it to them, but it's totally unnecessary, and in an exam situation, a total waste of time given time pressure.
Hope this helps