Homework Help: Chemistry

Posted by Anya on Thursday, December 13, 2012 at 2:35am.

determine the pH of a 0.116 M Ba(OH)2 solution at 25 degrees C.

i keep getting 13.06 for this answer, but the answer is 13.37 :S

what i do is i take the negative log of the concentration which is 0.9355 which is pOH.

i know that pH = 14 - pOH
so i get pH = 13.06

where am i going wrong ? :S

thanks for help in advance!

Chemistry - Anonymous, Thursday, December 13, 2012 at 2:45am
haha I'm guessing your studying off the old chemistry multiple choice exam for tommorow's chemistry exam at ryerson?
Chemistry - bobpursley, Thursday, December 13, 2012 at 2:52am
You assumed barium hydroxide is totally dissociated. The solubility product constant is 5E-3.
Chemistry - Anonymous, Thursday, December 13, 2012 at 3:15am
Anya, do you know how to do number 4 on the final chemistry exam. Please tell me.
Chemistry - Anya, Thursday, December 13, 2012 at 3:34am
i figured it out, i have to multiple the concentration by 2 because of the 2 hydroxides right?

and yes i do know # 4

you want to convert 0.0354 mg/mL at 1 atm to mol/L at 0.00036 atm.

so :

(0.0354 mg/mL) x ( 0.00036)
= 1.2744 x 10^-5 mg*CO / mL

then you just want to convert units)

1.27 *10^-5 mg*CO/mL is 1.27 * 10 ^-5 g/L

multiply that by 1 mole CO/ 28 g

yyou get 4.5 * 10 ^ -7
Chemistry - Anonymous, Thursday, December 13, 2012 at 4:04am
Yeah I see what you did. I did the same thing in a slightly different way and got 4.5X10^-5. I see my mistake now

you have:

P1/C1=P2/C2

-----------
P1=1 C1=0.0354
P2=0.00036 C2?
-----------

1/0.0354=0.00036/C2

then you cross multiplied and then converted the value 1.27X10^-5 from grams to mols.

================================

Do you know how to do 6 can you tell me?

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