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Ph question, I'm stuck

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jmxwell:
What is the pH of a solution resulting from the addition of 0.2 moles of lactic acid in 1L of distilled water? pKa = 3.85. What will be the pH after adding 0.1 M NaOH? And after adding an additional 0.1 moles of NaOH? And after adding 100 mL of water?
My thoughts:
M= n/V = 0.2/1 = 0.2 mol/L
pH of weak acids ⇒ pH = ½ * (pKa) - ½ * ([[acid])
pKa = 3.85
pH = ½ *(3.85) - ½ *log (0.2) = 1.925 + 0.35 = 2.27
After add NaOH
pH = 3.85 + log [(0.2+0.1/0.2-0.1)] ⇒ ph = 3.85 + 0.477 = 4.327

I would love to know if Im' doing well and how can I find last ph after 100 mL H20, Im' stuck with no toughts on it.

AWK:
For the second part do correct  stoichiometry of neutralization.

jmxwell:
But I can't understand, How does ph will decrease if he/she is adding a strong base to solution?
I can't figure out where is my error

AWK:
And if you add alkali to the water, the pH does not rise?

jmxwell:
Will increase, but you told my calculous are wrong in second part. ???

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