For all points show work Determination of Ka for a Weak Monoprotic Acid What is

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For all points show work

Determination of Ka for a Weak Monoprotic Acid What is the equilibrium constant expression for a weak acid? When is the equilibrium constant, Ka equivalent to the hydronium concentration? Explain What is pKa? What are the two methods to determine its value in the lab? What are the differences and similarities in the graph of pH versus volume of titrant for a strong acid compare to that of a weak acid? What is the buffer region in a graph of pH versus volume of titrant? What is the pH at the equivalent point in the titration of a weak acid versus a strong base? Why? What is a monoprotic acid? Diprotic acid? Give an example of each. Using the following graph estimate the Ka of the acid:

Explanation / Answer

8.

WE have the following:

At 10 mL, pH = 4.2
At 25 mL, pH = 8.0

(15.1 mL - 10 mL) / (25 mL - 10 mL) =0.34 . . .[15.1( 10+(25-10)*0.34) mL is 34%of the way between 10 mL and 25 mL.] Now find the pH that is 34% of the way between 4.2 and 8.0

8-4.2 = 3.8; 0.34 x 3.8 = 1.292; pH at 15.1 mL = pH at 10 mL + 1.292 = 4.2+1.292 = 5.492

pKa = 5.492 and Ka = 10^-pKa = 10^-5.492=3.22 * 10^-6

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