### Sig Figs

Posted:

**Wed Jan 23, 2019 4:13 pm**What are the sig fig rules for calculating pH and pOH? thank you!

Created by Dr. Laurence Lavelle

https://lavelle.chem.ucla.edu/forum/

https://lavelle.chem.ucla.edu/forum/viewtopic.php?f=49&t=40573

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Posted: **Wed Jan 23, 2019 4:13 pm**

What are the sig fig rules for calculating pH and pOH? thank you!

Posted: **Wed Jan 23, 2019 4:18 pm**

When calculating pH and pOH, count the number of sig figs given in the concentration and the pH/pOH should have that number of sig figs after the decimal. For example, if the pH=-log(1.4x 10^-6) then pH = 5.85 (two sig figs in 1.4 x 10^-6 and two after the decimal in 5.85).

Hope this helped!

Hope this helped!

Posted: **Wed Jan 23, 2019 4:20 pm**

Like said above, sig figs are a little bit different when dealing with pH and pOH because of what the log function does. A good rule is to just count sig figs in pH and pOH as the figures after the decimal point. This means that a pH of 1.2 has only one sigfig and 1.23 would have two. This rule only applies to pH and pOH as well as any other times you would apply a log such as pKa and pKb.

Posted: **Thu Jan 24, 2019 12:01 am**

When calculating pH and pOH, sig figs are calculated from the initial concentration and applied after the decimal of the pH/pOH