Weak Acid/Base Calculations

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Courtney McHargue 1I
Posts: 56
Joined: Fri Sep 28, 2018 12:17 am

Weak Acid/Base Calculations

Postby Courtney McHargue 1I » Mon Jan 14, 2019 8:24 pm

How do we find the pH/pOH and concentrations of H30+ and OH- of a reaction with a weak acid/base that doesn't completely dissociate?

aisteles1G
Posts: 117
Joined: Fri Sep 28, 2018 12:15 am

Re: Weak Acid/Base Calculations

Postby aisteles1G » Mon Jan 14, 2019 8:29 pm

You would have to make an ICE table and assume that -x amount dissociates and therefore +x amount protonates to form the products. Then you use the relationship between pKa and pKb to determine the concentrations. I watched a pretty helpful video on this: https://www.khanacademy.org/science/che ... quilibrium

Hope this helps!

Jayasuriya Senthilvelan 4I
Posts: 31
Joined: Thu Jan 10, 2019 12:17 am

Re: Weak Acid/Base Calculations

Postby Jayasuriya Senthilvelan 4I » Mon Jan 14, 2019 8:49 pm

I agree with the above. Weak acids and bases only dissociate partially. If the Ka or Kb is incredibly small, x (amount dissociated) is very very small.
For a Weak acid:
HA <--> H+ + A-
I
C
E

The equilibrium value for H+ can be used to then calculate the pH of the solution. Hope that was helpful.


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