Question about Casio FX-115MS Plus Calculator

# How to find pka value

How do I find the pka value using my calculator. What buttons do I press?

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• Anonymous Mar 22, 2014

calculate ph

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• Casio Master

Hello,
If I guessed right you are talking about the Chemistry notion of the pKa
Let the equilibrium constant be Ka =1.8x10^(-5). Then by definition pKa=-log(Ka) , log in base 10
pKa = - log(1.8x 10^(-5))
First set [MODE] to [COMP] by pressing [MODE] 1.
[LOG] [(] 1.8 [x] [SHIFT] [10 to the x] [(-)] 5 [)] . [(-)]
The [(-)] key is the change sign key : a small - between parentheses. The last [(-)] sign in the expression takes the negative of the whole calculation to obtain the correct value of the pKa.
The value you should find for the above exemple is 4.74

Hope it helps.

Posted on Sep 18, 2009

• k24674 Sep 18, 2009

Warning There is not dot before the last change sign symbol.
[LOG] [(] 1.8 [x] [SHIFT] [10 to the x] [(-)] 5 [)] [(-)]

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Posted on Jan 02, 2017

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