Sig Figs for pH

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Annie Chantasirivisal_4G
Posts: 114
Joined: Wed Sep 18, 2019 12:21 am

Sig Figs for pH

Postby Annie Chantasirivisal_4G » Sun Dec 01, 2019 8:27 pm

The book states:
"A Note on Good Practice: The number of digits following the decimal point in a pH value is equal to the number of significant figures in the corresponding molar concentration, because the digits preceding the decimal point simply report the power of 10 in the data (as in log 10^5 = 5)."

I had to read that sentence a couple of times before I kind of understood it, and even then I'm not sure, so I want to make sure:

The book example is:
pH = −log(1.0 × 10^−7) = 7.00
so because 1.0 has 2 sigfigs, 7.00 would need 2 sig figs after the decimal, right?

So if the concentration was 1.0 × 10^−14 mol.L^-1, the pH would then be 14.00?

Thanks for any clarification!

ishaa Diwakar 4E
Posts: 56
Joined: Wed Sep 11, 2019 12:17 am

Re: Sig Figs for pH

Postby ishaa Diwakar 4E » Sun Dec 01, 2019 8:31 pm

Yes, exactly. The sig figs from any other numbers in the question should be used to dictate the number of sig figs after the decimal place in your pH answer.

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