KristenD77

Predent
5+ Year Member
Apr 29, 2012
205
25
Hello can someone please help me with this problem. I'm having the hardest time figuring it out.

If the pH is 4.9 what is the [OH-]

So I know that the pOH is -9 so the [OH-] would be 10^ -9 but the answer is 7.9 x 10 ^ -10

I really can't figure out how to get that number without a calculator
Help would be GREATLY appreciated!
 
Last edited:

KristenD77

Predent
5+ Year Member
Apr 29, 2012
205
25
POH = 14 - 4.9 = 9.1
10^-9.1 = 7.9*10^-10

You're getting 10^-9 because when you approximate you get 1*10^-9.

9.1 will give you slightly less than 1 (0.79), and you have to give your answer in proper scientific notation, which is 7.9*10^-10.
Thank you so much!
 
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