Question

Enough of a monoprotic acid is dissolved in water to produce a 1.67 M solution. The pH of the resulting solution is 2.54. Calculate the Ka for the acid.

Answer 1

write a dissociation equation and it's equilibrium expression

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Equilibrum expression.

e.g. aA + bB \(\rightleftharpoons\) cC + dD

\(K_{fwd}=\dfrac{[C]^c*[D]^d}{[A]^a*[B]^b}\)
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you're given pH, so you can figure out \([H_3O^+]\), also written as \([H^+]\), with:

\(pH=-log[H_3O^+]\)

then figure the rest of the concentrations in the expression.