Phenylacetic acid (C6H5CH2COOH) is one of the substances that accumulates in the blood of people with phenylketonuria, an inherited disorder that can cause mental retardation or even death. A 0.021 M solution of C6H5CH2COOH has a pH of 2.99. Calculate the Ka value for this acid.

Question

what equation do i use?

Answer 1

Call that long name HP (which doesn't have anything to do with pH).

pH = 2.99
2.99 = -log(H^+)
(H^+) = 0.00102

.........HP ==> H^+ + P^-
I.....0.021.....0......0
C........-x.....x.....x
E......0.021-x..x.....x

Ka = (H^+)(P^-)/(HP)
Substitute 0.00102 for x and 0.021-0.00102 for HP and solve for Ka.

Answer 2

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