Sig Figs for Calculating pH and pOH

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Thuy-Anh Bui 1I
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Sig Figs for Calculating pH and pOH

Postby Thuy-Anh Bui 1I » Sun Dec 03, 2017 3:13 pm

For calculating logarithms/pH/pOH, the number of sig figs comes from the mantissa aka after the decimal place. However, for some problems (such as 12.27 and 12.29), the solutions manual does not acknowledge this. If the calculation was pH=-log(0.025) (2 sig figs), wouldn't the answer be 1.60 with the 2 sig figs shown in the decimal place?

Alex Leve 3F
Posts: 20
Joined: Fri Sep 29, 2017 7:07 am

Re: Sig Figs for Calculating pH and pOH

Postby Alex Leve 3F » Sun Dec 03, 2017 3:19 pm

Yes, I believe you are correct about the number of significant figures that the solution should have.

Camille Ng 1D
Posts: 18
Joined: Thu Jul 27, 2017 3:01 am

Re: Sig Figs for Calculating pH and pOH

Postby Camille Ng 1D » Mon Dec 04, 2017 3:02 pm

Yes, just use the same amount of sig figs that are given in the question for your solution.

Ishan Saha 1L
Posts: 60
Joined: Fri Sep 29, 2017 7:03 am

Re: Sig Figs for Calculating pH and pOH

Postby Ishan Saha 1L » Mon Dec 04, 2017 3:17 pm

1.60 actually has 3 sig figs, because all 0's after nonzero values after the decimal count as sig figs. I believe the correct answer would be 1.6, with 2 sig figs as was used in the original question.

Suhail Zaveri
Posts: 24
Joined: Sat Jul 22, 2017 3:01 am

Re: Sig Figs for Calculating pH and pOH

Postby Suhail Zaveri » Mon Dec 04, 2017 4:52 pm

Hello,

Usually the pH is calculated by counting two digits after the decimal, usually the sig figs will be counted after the decimal place so 1.66 has two significant figures.

Hope this helps


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