finding pH

thebillsfan

Unseasoned Veteran
10+ Year Member
5+ Year Member
What's the pH of a solution that has a hydroxide ion concentration of 6*10^-6?

I know this is easy, but I tried finding it using the pH+pOH=14 method and was not successful. The actual pH is 9.77 if you do 1*10^-14/6*10^-6 to get the [H] and then take the pH from there.

However, if you try and find the pOH of 6*10^-6, you get something between 5 and 6. Subtracting this from 14 you should get a number between 8 and 9, not 9 and 10. What am I doing wrong?

kentavr

10+ Year Member
What's the pH of a solution that has a hydroxide ion concentration of 6*10^-6?

I know this is easy, but I tried finding it using the pH+pOH=14 method and was not successful. The actual pH is 9.77 if you do 1*10^-14/6*10^-6 to get the [H] and then take the pH from there.

However, if you try and find the pOH of 6*10^-6, you get something between 5 and 6. Subtracting this from 14 you should get a number between 8 and 9, not 9 and 10. What am I doing wrong?
The answer is 8.77 by both methods

ezsanche

10+ Year Member
5+ Year Member
What's the pH of a solution that has a hydroxide ion concentration of 6*10^-6?

I know this is easy, but I tried finding it using the pH+pOH=14 method and was not successful. The actual pH is 9.77 if you do 1*10^-14/6*10^-6 to get the [H] and then take the pH from there.

However, if you try and find the pOH of 6*10^-6, you get something between 5 and 6. Subtracting this from 14 you should get a number between 8 and 9, not 9 and 10. What am I doing wrong?
1st method:
Kw = [H][OH] which can be rearranged to Kw/[OH]= [H]
10^-14 / 6 x 10-6= .166 x 10^-8 or 1.66 10^-9

PH= -log 1.66 x 10^-9 = 8.78

2nd method:
POH = -log 6 x 10^-6 which is about 5.22
Now using the equation POH + PH = 14
and solving for PH we get 14-PH or 14-5.22 = 8.78 = POH

I get the same results regards of which method I use.

OP
T

thebillsfan

Unseasoned Veteran
10+ Year Member
5+ Year Member
damnit kaplan got their answer wrong. everything about that answer key was wrong! i didnt check their math with my own calculator, sorry for making you do that. **** kaplan