Answer to Question #125918 in Physical Chemistry for Cole

Question

A 0.187 M weak acid solution has a pH of 3.99. Find Ka for the acid.
Express your answer using two significant figures.

Answer 1

A 0.187 M weak acid solution has a pH of 3.99.

pH of 3.99. = 4 ( approx ) .

[H⁺] = 10^-4 M .

A 0.187 M weak acid solution = C .

CONCENTRATION OF H⁺ = UNDER ROOT ( C* Ka ) . .

So , Ka = [H⁺]² / C . .

So , K_a = 10^-8 / 0.187 . = ( 5.347 * 10 ^-8 ) .( Approx . ) . Answer .........