Question

100 mL of a 0.10 mol L^-1 solution of sodium hydroxide is diluted with distilled water. The pH of the diluted solution is 12.00. What is the volume of the distilled solution?

Answer 1

1. Find moles present in the 0.1M (molarity) solution
100mL = 0.1L
To solve for moles use the formula

Molarity = moles/Liters

2. Use these relations to find concentration of the new solution
pH + pOH = 14
pOH = - log([OH-])
Where the square brackets mean concentration so [OH-] is the concentration of hydroxide.

Realize that:
NaOH -> -OH + Na+
so moles of NaOH = moles of -OH
therefore, Molarity of NaOH = Molarity of -OH in the solution

3. Plug in the molarity of NaOH which you found in step 2 and moles of NaOH which you found in step 1 into:

Molarity = moles/Liters

Solve for Liters and you have the new volume of your solution

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If you have any further questions feel free to ask.

Answer 2

As an aside the reason Moles of NaOH = Moles of -OH is because NaOH is a strong base therefore it is assumed that when in aqueous solution (water) it completely dissociates into -OH and Na+ ions. If this a weak base or acid you could not make that assumption you would have to use dissociation constants.

Answer 3

oh SILLY ME xD... I forgot that it's [OH-] not [H+] xD
THANKS SO MUCH :)))
I know where i went wrong now LOL

Answer 4

For step 3 it should say moles not molarity in step 1

Answer 5

i ended up with a final volume of 1 litre O_O

Answer 6

moles = 0.10M*0.1L = 0.01mol
pOH = 2
10^-2 = [-OH] = 0.01M

0.01mol/x = 0.01M

x = 1L

good job

Answer 7

oh YAYY :)
Thanks a bunch :D !!