pH sig figs

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Malia Shitabata 1F
Posts: 127
Joined: Sat Aug 17, 2019 12:17 am

pH sig figs

Postby Malia Shitabata 1F » Sat Jan 18, 2020 1:39 pm

When you have pOH and you're trying to find the pH should the pH have the same number of decimal places as the pOH? For example, if your pOH is 2.735 would you subtract from 14 or 14.000 or something in between? Because I feel like if you subtract from 14 and round based on decimal places then it can be more inaccurate because it's a difference of 11 pH vs 11.265 pH

Sanjana Munagala_1j
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Joined: Sat Aug 24, 2019 12:17 am
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Re: pH sig figs

Postby Sanjana Munagala_1j » Sat Jan 18, 2020 1:46 pm

Yes it would reflect the number of decimal places of pOH. 14.00 is just a set number, for example when you would use molar mass. You can adjust the number of decimal places in Kw to match with the decimal places in pOH.

Hope that helps!

Alice Chang 2H
Posts: 101
Joined: Fri Aug 30, 2019 12:18 am

Re: pH sig figs

Postby Alice Chang 2H » Sat Jan 18, 2020 3:28 pm

If your pOH value has 3 sig figs (counted after the decimal!), you use that to calculate your pH by subtracting from 14.000 (has 3 sig figs as well)
There's a worksheet on the chem 14B website that explains sig figs further if you need more help :)

Abhi Vempati 2H
Posts: 104
Joined: Fri Aug 09, 2019 12:17 am

Re: pH sig figs

Postby Abhi Vempati 2H » Sat Jan 18, 2020 5:29 pm

This link on the Chem 14B website (titled "Everything you want to know about Significant Figures") was really helpful for me: https://lavelle.chem.ucla.edu/wp-conten ... OUT_SF.pdf

The second page has the rules for logarithms, and I hope it helps!

Brandon Valafar
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Re: pH sig figs

Postby Brandon Valafar » Mon Jan 20, 2020 12:02 pm

From what I understand, you do the least amount of sig figs in the problem behind the decimal for pH. The link on Lavelle's website has a more in depth description though.

805097738
Posts: 180
Joined: Wed Sep 18, 2019 12:20 am

Re: pH sig figs

Postby 805097738 » Mon Jan 20, 2020 12:30 pm

One of the UAs said that the amount of sig figs in the problem is the amount of sig figs you place after the decimal for pH


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