# How to find pKa based on pH and concentration?

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I'm given the concentration of lactic acid as 0.025 M and its pH as 2.74.

Here's what I did:

#[H^+]=10^(-2.74)\approx 1.82\times10^(-3)M#

#K_a=\frac(x^2) (0.025-x )=\frac((1.82\times10^(-3))^2) (0.025-(1.82\times10^(-3)))\approx 1.4\times10^(-4)#

And then I found pKa by taking #-log(1.4\times10^-4)\approx3.9# .

Have I done this correctly?

I'm given the concentration of lactic acid as 0.025 M and its pH as 2.74.

Here's what I did:

And then I found pKa by taking

Have I done this correctly?

##### 1 Answer

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Dave
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Mar 11, 2018

#### Answer:

The setup is correct.

#### Explanation:

I didn't recalculate your numbers, but your setup is right. Well done.

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