how to find pH

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Kellylin_4D
Posts: 66
Joined: Sat Aug 24, 2019 12:17 am

how to find pH

Postby Kellylin_4D » Mon Dec 02, 2019 3:41 pm

other than when the question gives you the mole, how do you find pH? For example, how would you get pH from pKa? What are other question formats that leads to pH?

AKhanna_3H
Posts: 104
Joined: Wed Sep 18, 2019 12:19 am

Re: how to find pH

Postby AKhanna_3H » Mon Dec 02, 2019 3:51 pm

According to a previous post, Dr. Lavelle said that we would not have to calculate one from the other, but it is important to know that when you put an acid in a solution with a pKa less than the pH of the solution the acid will dissociate.

Subashni Rajiv 1K
Posts: 101
Joined: Wed Sep 18, 2019 12:16 am

Re: how to find pH

Postby Subashni Rajiv 1K » Mon Dec 02, 2019 4:38 pm

If the pH of the acid and conjugate base are known, you can use the equation pH = pKa + log [A-]/[HA].

Ryan Yee 1J
Posts: 101
Joined: Sat Aug 17, 2019 12:16 am

Re: how to find pH

Postby Ryan Yee 1J » Mon Dec 02, 2019 6:57 pm

Since pH = -log[H3O+], you could use antilog to go from pKa to Ka, and then use Ka = [H3O+][A−]/[HA] to solve for the H3O+ that you need. Unfortunately, you will need to be given more information in order to solve for pH this way.

Jamie Lee 1F
Posts: 106
Joined: Fri Aug 09, 2019 12:16 am

Re: how to find pH

Postby Jamie Lee 1F » Mon Dec 02, 2019 7:45 pm

There are some questions in 6B that ask you to find pH. For example, you can go from the given concentration of an acid to pH by using -log([H3O+]=pH. You could also be given an M1V1=M2V2 type question like 6.B #5.d. The last question form I can think of is being asked to find pOH, and converting that to pH by subtracting pOH from 14.


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