February 20, 2017

Homework Help: Dr Bob

Posted by Andrew on Sunday, January 11, 2009 at 7:15pm.

What is the pH of the solution that results from mixing 5 ml of 0.2 M NaOH and 100 mL of 0.05 M lactic acid? (Pka of lactic acid= 3.86)

Use the Henderson-Hasselbalch equation. The mixture you have indicated will react to form a buffer, the base will be the sodium lactate and the acid will be the lactic acid not neutralized by the NaOH. Post your work if you get stuck.

I know that I'm supposed to use the equation:

pH= pKa+log(deprotnated, which case the lactic acid not neutralized)/(protonated, sodium lactate)

but I'm not sure where the numbers come into play. i got that initally there are 0.001 mol of NaOH and 0.005 mol of lactic acid. I tried doing limiting reagents and got that the products each get 0.001 mol? which would give the ratio of 1, which i don't think is right...

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