Question about Texas Instruments TI-30XA Calculator

# I would like to calculate pKa for 2.35. What button to push first?

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Posted on Jan 02, 2017

SOURCE: How to find pka value

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

You need the [EE] key to enter powers of 10 exponents.
You need the change sign key [+/-] key.
You need the [LOG] key.

pKa: 6.5 [EE] [+/-] 5 [LOG] [+/-]
There are two change sign: The first (either before or after the exponent 5), the last is entered after you press the log key , so as to negate (make negative if result is positive, and make positive is result is negative) the value.
The result should be 4.1870866 or 4.19

Posted on Mar 08, 2010

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### I need to punch in: -log 10 Ka to get pKa,how do i do that? let's say Ka = 1.75 X 10^-5 the answer = 4.76 pKa = -log 10 Ka show me step by step how to punch in. thanks!

(-) LOG 1 . 7 5 EE (-) 5 ENTER

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pKa: 6.5 [EE] [+/-] 5 [LOG] [+/-]
There are two change sign: The first (either before or after the exponent 5), the last is entered after you press the log key , so as to negate (make negative if result is positive, and make positive is result is negative) the value.
The result should be 4.1870866 or 4.19

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To calculate the pKa you use the key labeled [LOG], just above [COS]. Be careful with the negative sign: For that, you use the key [(-)] just above the RCL key. Press the keys in the order specified below

pKa = [(-)] [LOG] number [ ) ] [=]

Although the right parenthesis is not required in this particular case, it is better to accustom oneself to close the parenthesis.

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### How to find pka value

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.

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