Hypochlorous acid is a weak acid, as indicated by the extremely small ionization (Ka) value.
As such, when the acid is an aqueous environment, the following equilibrium reaction will occur:
HClO + H2O <---> H3O+ + ClO-
Create an ICE table, which is a useful organization tool in equilibrium chemistry.
HClO + H2O <---> H3O+ + ClO-
I 0.0684 0 0
C -x +x +x
E 0.0684 x x
I stands for initial concentrations; C for change; and E for equilibrium concentrations. The reason why E for HClO is the same as I is because the dissociation constant is much smaller than the initial concentration, which means assuming the HClO concentration did not change is acceptable.
Ionization constant = [H3O+][ClO-] / [HClO]
[H3O+] = sqrt(3.5e-8 x 0.0684)
pH = -log[H3O+] = 4.31
English
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Thanks, but it's too late. I already failed both the assignment and my most recent quiz. Friggin' hell.