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Inessa05 [86]
3 years ago
12

What is the percent dissociation of 0.187 M weak acid (HA) with a Ka of 4.3x10-7 at 18.9°C? Enter to 2 decimal places.

Mathematics
1 answer:
Fudgin [204]3 years ago
5 0

Explanation:

Let the reaction equation for the dissociation of weak acid is as follows.

                      HA \rightarrow H^{+} + A^{-}

Initial:         0.87            0         0

Change:      -x               +x         +x

Equilibrium:  0.87 - x    +x         +x

Hence, expression for the dissociation constant will be as follows.

           k_{a} = \frac{[H^{+}][A^{-}]}{[HA]}

Now, putting the given values into the above formula as follows.

        k_{a} = \frac{[H^{+}][A^{-}]}{[HA]}

       4.3 \times 10^{-7} = \frac{x \times x}{(0.187 - x)}

               x = 0.000283

Hence, at equilibrium the concentration of hydrogen ions is 0.000283.

or,     [H^{+}] = 2.83 \times 10^{-4}

            [H^{+}] = C \times \alpha

Also,   \alpha = \frac{[H^{+}]}{C}

                      = \frac{0.000283}{0.187}

                      = 0.00151

And, the percentage of dissociation is 0.00151 \times 100 = 0.151%

Thus, we can conclude that percent dissociation of given weak acid is 0.151%.

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