Question: The pH is defined for our present purposes as pH = - log 10 ([H + ]/c). Find the pH of a solution formed from

The pH is defined for our present purposes as

pH = - log10 ([H+]/c°).


Find the pH of a solution formed from 0.075 mol of NH3 and enough water to make 1.00 l of solution. The ionization that occurs is

NH3 + H2O ⇋ NH+4 + OH-.


The equilibrium expression in terms of molar concentrations is

([NH1/c°) ([OH 1/c°) x (H2O)([NH3]/c°) (INH]/c°)([OH-]/c°) ([NH3]/c°)


where x(H2O) represents the mole fraction of water, which is customarily used instead of its molar concentration. Since the mole fraction of the solvent in a dilute solution is nearly equal to unity, we can use the approximate version of the equation. The base ionization constant of NH3, denoted by Kb, equals 1.80 × 10-5 at 25°C.

([NH1/c) ([OH 1/c) x (H2O)([NH3]/c) (INH]/c)([OH-]/c) ([NH3]/c)

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