A solution contains 4.25 g ammonia per 250.0 ml of solution. Electrical conductivity measurement at 25°C show that 0.40% of the ammonia has reacted with water. The pH of the solution is (log 2 = 0.3)

Question

Prashant Kotian · Accepted Answer

Correct answer: A. Molar mass of = 17 g/mol. Moles of = 4.25 / 17 = 0.25 mol. Volume of solution = 250 mL = 0.25 L. Concentration C = 0.25 / 0.25 = 1.0 M. Degree of dissociation α = 0.40% = 0.004. [OH-] = C × α = 1.0 × 0.004 = 4.0 × 10^-3 M. pOH = -log[OH-] = -log(4.0 × 10^-3) = 3 - 2 log 2 = 3 - 0.6 = 2.4. pH = 14 - pOH = 14 - 2.4 = 11.6.

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