Sig Figs for ph/pOH calculations

Ryan Chang 1C
Posts: 105
Joined: Sat Aug 24, 2019 12:17 am

Sig Figs for ph/pOH calculations

Just wanted to bring up that the sig fig rules for ph/pOH calculations are different than the rules for normal sig figs. If you are given 3 sig figs in a question, your final answer doesn't necessarily have 3 sig figs, but rather has 3 decimal places. Here is an example:

0.012 M of H3O+ = -log(0.012) = 1.92

Although there are only 2 sig figs in the given concentration of H3O+, the final answer is 1.92 because the amount of sig figs in the given amount indicates the amount of decimal places the answer should have. In this case, 2 sig figs means 2 decimal places, which is why 1.92 is correct although it has 3 sig figs. 1.9 would not be the correct answer.

Maia_Jackson_2C
Posts: 101
Joined: Fri Aug 30, 2019 12:17 am

Re: Sig Figs for ph/pOH calculations

I haven't heard this mentioned anywhere else, did he mention it in lecture? and should we do it this way on the final?

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