Weak acids and equations

Acidity
Basicity
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AlexNguyen15
Posts: 66
Joined: Fri Sep 25, 2015 3:00 am

Weak acids and equations

Postby AlexNguyen15 » Fri Nov 20, 2015 7:51 pm

For weak acids when writing the proton transfer equilibrium equation will there also be a Ka and Kb? Is this characteristic of weak acids and bases? Can anyone explain any of these concepts for me?

Nathan Danielsen 1G
Posts: 17
Joined: Fri Sep 25, 2015 3:00 am

Re: Weak acids and equations

Postby Nathan Danielsen 1G » Sat Nov 21, 2015 12:12 pm

Ka is the measure of the concentration of H3O+ ions in a solution. All acids have a Ka, but we can calculate the Ka(using the equilibrium equation) of a weak acid because some of the original acid remains in the solution, unionized. Kb is the concentration of OH- ions in a solution. An acid will not produce OH-, so the Kb of the reaction between a week acid and water is simply Kw/Ka. Conversely, a weak base will produce OH- in water, but does not ionize completely. Therefore you can calculate the Kb of this reaction and use the equation Kw/Kb, to find the Ka. Remember, since strong acids and bases ionize completely in solution, you cannot calculated their Ka and Kb values.

Rachel Lipman
Posts: 45
Joined: Fri Sep 25, 2015 3:00 am

Re: Weak acids and equations

Postby Rachel Lipman » Sat Nov 21, 2015 2:37 pm

Are Ka and Kb inversely proportional? I remember going over some aspect of the relationship in class...

Neel Patel - 2A
Posts: 48
Joined: Fri Sep 25, 2015 3:00 am

Re: Weak acids and equations

Postby Neel Patel - 2A » Sat Nov 21, 2015 2:42 pm

Ka and Kw are related by the following relation Ka * Kb = Kw. So if you solve for Ka, you would take reciprocal of Kb and multiple that by Kw. So in essence Ka and Kw are inversely proportional.


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