Hello!
The chemical equation for the dissociation reaction is the following:
CH₃CH(OH)COOH + H₂O ⇄ CH₃CH(OH)COO⁻ + H₃O⁺
The expression for the equilibrium constant Ka is the following:
[tex]Ka=\frac{[CH_3CH(OH)COO^{-}][H_3O^{+}]}{[CH_3CH(OH)COOH]} [/tex]
For calculating the concentration of H₃O⁺ we need to clear from this last equation:
[tex]Ka=\frac{[CH_3CH(OH)COO^{-}][H_3O^{+}]}{[CH_3CH(OH)COOH]} \\ \\ Ka=\frac{[x][x]}{[1,75M-x]} ---(1,75M-x\approx 1,75M) \\ \\ \sqrt{6,4*10^{-5}*(1,75M)}=x=0,0106M=[ H_3O^{+}][/tex]
So, the concentration of H₃O⁺ will be 0,0106 M
Have a nice day!