Acids & Bases - Chemistry

Acids & Bases 38Example: What is the pH of a 0.1 M solution ofammonia? K b ≅ 1 × 10 −5Init: 0.1 M 0 M 0 M:NH 3 (aq) + H 2 ONH 4 + (aq) + OH − (aq)@ Eq: 0.1 - x x xSubstitute our x values into the equilibriumexpression and solve for x:[ NH+ −4 ][ OH ]− 5Kb= = 1×10[N H ]( x)( x)(0.1 − x)3= 1×10− 5But, this will be a quadratic expression and thequadratic formula is needed to exactly solve for x(ugh!).But lets use the very good approximation fromweak acid equilibria problem solving that willdramatically simplify the algebra.