# chemistry

What mass in grams of potassium hydroxide is contained in 500 mL of solution that has a pH of 11.5?

I have a pOH of 2.5

to get [OH]

I do 10^-2.5 to get 0.001581138

Then I divide this by 2 to find the mols in 500 mL

Then, grams = mols x molar mass

= 0.00158``38 x 56.105 g/mol

=0.08 g

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1. What mass in grams of potassium hydroxide is contained in 500 mL of solution that has a pH of 11.5?

I have a pOH of 2.5 OK

to get [OH]

I do 10^-2.5 to get 0.001581138
No, (OH^-) = 0.00316 M

Then I divide this by 2 to find the mols in 500 mL
0.00316/2 = 0.00158 mols in 500 mL.
Then, grams = mols x molar mass

= 0.00158``38 x 56.105 g/mol
I don't know what the ``38 is. Also, you took 0.00158, divided by 2 and still came out with 0.00158? I think you lost track of what you were typing here. 0.00158 mol in 500 is the correct number.
=0.08 g
0.00158 mols x 56.105 g/mol = 0.08865 g which I would round to 0.0886 g KOH.
Why is my answer wrong? My best guess is that you truncated the number to 0.08 g instead of keeping the other two places of 0.0886 g Check my work.

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posted by DrBob222
2. Wow , thanks you are a really excellent expert!
:)

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posted by Ross

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