About us | Feedback

pH calculation - questions

pH questions

BATE pH calculator

operating systems:
XP, Vista, 7, 8, 10

single user license price:
€24.95 - approximately $25

Buy Now!

By clicking Buy Now! you will continue to the FastSpring checkout page where payment will be taken, and your order fulfilled by FastSpring, our trusted reseller, and Merchant of Record.

download 30-day free trial!
30-day money back guarantee!

pH calculation questions » finding pKa of weak acid

0.1 M solution of weak acid has pH=4.0. Calculate pKa.

If pH=4.0 then [H+]=10-4 - that means that the dissociation fraction is about
10-4/0.1×100%=0.1% - well below 5%. That in turn means that pH of the solution is described by the simplified formula 8.13:

eq. 8.138.13

All we have to do is rearrange to get the equation for Ka:

Plugging numbers in we get Ka=(10-4)2/0.1=10-7, so pKa=7.

Our pH calculator can help us check this result - and indeed, entering 0.1 as concentration and 7 as pKa we get pH=4.0 which confirms our calculations.


Chemical calculator software for pH calculation, concentration conversion solution preparation and chemical equation balancing chemical calculator