Explanation:
Let the reaction equation for the dissociation of weak acid is as follows.
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]}](https://tex.z-dn.net/?f=k_%7Ba%7D%20%3D%20%5Cfrac%7B%5BH%5E%7B%2B%7D%5D%5BA%5E%7B-%7D%5D%7D%7B%5BHA%5D%7D)
Now, putting the given values into the above formula as follows.
![k_{a} = \frac{[H^{+}][A^{-}]}{[HA]}](https://tex.z-dn.net/?f=k_%7Ba%7D%20%3D%20%5Cfrac%7B%5BH%5E%7B%2B%7D%5D%5BA%5E%7B-%7D%5D%7D%7B%5BHA%5D%7D)

x = 0.000283
Hence, at equilibrium the concentration of hydrogen ions is 0.000283.
or, ![[H^{+}] = 2.83 \times 10^{-4}](https://tex.z-dn.net/?f=%5BH%5E%7B%2B%7D%5D%20%3D%202.83%20%5Ctimes%2010%5E%7B-4%7D)
![[H^{+}] = C \times \alpha](https://tex.z-dn.net/?f=%5BH%5E%7B%2B%7D%5D%20%3D%20C%20%5Ctimes%20%5Calpha)
Also, ![\alpha = \frac{[H^{+}]}{C}](https://tex.z-dn.net/?f=%5Calpha%20%3D%20%5Cfrac%7B%5BH%5E%7B%2B%7D%5D%7D%7BC%7D)
= 
= 0.00151
And, the percentage of dissociation is
= 0.151%
Thus, we can conclude that percent dissociation of given weak acid is 0.151%.