Maleic acid is used to retard the breakdown of fats. Imagine that you prepared a

Question

Maleic acid is used to retard the breakdown of fats. Imagine that you prepared a buffer by adding 14.35 millimoles of maleic acid and 20.57 millimoles of sodium hydrogen maleate to a 250.0mL volumetric flask which you brought to the mark with DI water. What is the pH of the soultion after your lab partner adds 10.00mL of 0.1336M KOH to the flask? Ka values for maleic acid are Ka1=1.20x10^-2 and ka2=5.96x10^-7

Explanation / Answer

Since ka2 is very small, we will ignore the second equilibrium where the disodium maleate is formed. Assuming equilibrium 1 Maleic acid -----> maleate + H+ conc of maleic acid = [MA](Maleic acid) = 14.35/250 (since total volume is 250 ml) [maleate] = 20.57/250 on adding KOH MA + OH- ------> MA- + H20 [OH]=0.1336*( 10/1000) since OH is a strong base the above reaction goes to completion. Now [MA] = 14.35/250 - [OH] [MA-] = 20.57/250 + [OH] using pH = pka1 + log ([MA-]/[MA]) pH = 1.747

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