Can someone quickly recap me on what the pH would be of a salt from a weak acid and weak base. (1 Viewer)

[lmao1010]

I low-key remember it as not being possible to calculate but not too sure. Can someone explain.
Like strong acid weak base is acidic salt
Etc so what bout weak acid and weak base

 

[Aditya_Raghu]

Yes ican help you im really good in chemistry

 

[lmao1010]

Yes ican help you im really good in chemistry

Ah good is it possible for you to explain?

 

[jazz519]

With HSC knowledge how the questions are asked you can't do it

This ties into the problem with the simple definitions of strong and weak acids learnt in HSC. A strong acid ionises fully while weak acid ionises partially.

So even an acid that has 90% ionisation in this definition would be weak.

It's not a good way to define it because if you were to compare a 5% ionisation acid vs 90% ionisation acid, then obviously the 90% ionisation one is a stronger acid but its hard to tell this without being given numbers in an exam.

The same logic compares to reaction of acid and base. You could have a weak acid and weak base but one of them might be stronger than the other. Without some data indicating that then it's basically impossible with hsc understanding of acid and base strength to figure that out since you don't really learn about what makes an acid or base stronger which is linked to things like electronegativity and bond strength

Due to that this type of question won't be asked in a hsc exam and is why in the syllabus dot point in mod 6 they don't list weak acid + weak

You could work it maybe from the Ka and Kb values if given, however based on how they ask these questions in hsc where this information is not usually included in these types of salt pH questions, I'd say it is unlikely to be something you need to know

 

[Run hard@thehsc]

If we assume that both the weak acid and weak base ionise to the same extent, can we conclude that the pH will have to roughly about 7? (At least in terms of titration curves)...

 

[jazz519]

If we assume that both the weak acid and weak base ionise to the same extent, can we conclude that the pH will have to roughly about 7? (At least in terms of titration curves)...

Yeah but like this is unlikely for you to have an acid and base like that. Also weak acid and base titration graphs aren't very clear like those involving strong acid/base as you can see in the image above by the other user

 

[Run hard@thehsc]

@jazz519 got it thanks!