Question

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


For Further Reading


chemistry - DrBob222, Sunday, April 6, 2008 at 12:09am
pH = 11.5
pOH = 14 - 11.5 = 2.5
pOH = -log(OH^-) ] 2.5
(OH^-) = ??
KOH ==> K^+ + OH^-
This is a strong base.
You have the (OH^-) which is mols/L. Take 1/2 that to find the mols in 500 mL, Then grams = mols x molar mass. Post your work if you get stuck

[OH] = 1.0 x 0^-14 / 11.5

= 8.69 x 10^-16 / 2

= 4.34 x 10^-16

g = 4.34 x 10^-16 x 56.10564 g/mol

= 2.4 x 10^-15

I got a wrong answer what ma I doing that's incorrect?

Answer 1

pH = 11.5
pOH = 14 - 11.5 = 2.5
pOH = -log(OH^-) ] 2.5
(OH^-) = ??
KOH ==> K^+ + OH^-
This is a strong base.
You have the (OH^-) which is mols/L. Take 1/2 that to find the mols in 500 mL, Then grams = mols x molar mass. Post your work if you get stuck

[OH] = 1.0 x 0^-14 / 11.5 <b>This isn't correct. If the pH is 11.5, then the pOH = 14 - 11.5 = 2.5 = pOH and (OH^-) = 0.00316 M. It appears to me that you have Kw mixed up with pKw.</b>

= 8.69 x 10^-16 / 2

= 4.34 x 10^-16

g = 4.34 x 10^-16 x 56.10564 g/mol

= 2.4 x 10^-15