In a 0.738 m solution, a weak acid is 12.5% dissociated. calculate ka of the acid.

Ka == 1.153 × 10^-4

Weak acid is HA;

Equilibrium: HA(aq) + H2O(l) <=> H3O^+(aq) + A^-(aq)

Ka = [H3O^+][A^-]/[HA]  

[H3O^+] = [A^-] = (0.0125)(0.738)

                         = 0.00923 M and [HA]

                         = 0.738 M - 0.00923 M = 0.738 M because the value 0.00923  is insignificant in this case.  

Ka = (0.00923)^2/(0.738)

     = 1.153 × 10^-4

organisms are more likely to be more preserved in mud than sand because mud is moist and wet, while sand is very dry.