Question

What ratio of concentration of ammonia and ammonium chloride should be mixed to
prepare a buffer solution of pOH 5? (Kb for NH3 =1.8 x 10-4)​

Answer 1

The ratio of concentration of ammonia and ammonium chloride : 0.05

Further explanation

Given

pOH=5

Kb for NH3 =1.8 x 10-4

Required

The ratio of concentration of ammonia (NH₃) and ammonium chloride(NH₄Cl)

Solution

Solutions containing ammonia and its salt: ammonium chloride are called alkaline buffers

Can be formulated : ( for the same of the volume, mol=concentration)

$\tt \displaystyle [OH-]=Kb\times\frac{weak\:base\:mole}{salt\:mole\times valence}$

pOH=-log [OH⁻]

pOH=5⇒[OH⁻]=10⁻⁵

Valence for NH₄Cl = 1, so the concentration ratio :

$\tt 10^{-5}=1.8\times 10^{-4}\times \dfrac{[~NH_3]}{[NH_4Cl]}\\\\0.05=\dfrac{[~NH_3]}{[NH_4Cl]}$