- #1

- 53

- 0

## Homework Statement

How many moles of OH–

are required to raise the pH of 4.00 liters of 25 mM glycine, pH 1.90, to a final pH of

9.70? Assume that the addition of OH–

does not change the volume of the solution.

## Homework Equations

I know at some point I will need to use the henderson hasselbalch equation, which is:

pH = pKa + log [Base]/[Acid].

## The Attempt at a Solution

I started by using the final pH of 9.70, the average pKa of glycine (the pKa of the isoelectric point) which is 5.97, and converting 25mM into 0.025M. This gives the equation of

9.70 = 5.97 + log [Base]/[0.025-Base]

If we set the Base equal to x. we get:

9.70 = 5.97 + log [X]/[0.025-X]

Which becomes

3.73 = log [X]/[0.025]

I am stuck here. My teacher gave us the answer as 0.12 mol of OH is needed, but there was no work shown on how to get there. Any help would be greatly appreciated. Thank you.