Question & Answer: Calculate the pH of a buffer that is 0.321 NH_3 AND 0.123M NH_4Cl……

Calculate the pH of a buffer that is 0.321 NH_3 AND 0.123M NH_4Cl.

Expert Answer

Answer

This solution is a buffer solution. And a buffer solution is one which maintains a fairly constant pH.

Kb for NH3 = 1.8 x 10^-5 from literature

Calculate PKb from Kb
pKb = -log Kb
pKb = -log 1.8 x 10^-5
pKb= 4.7447
By using Henderson-Hassel Balch Equation for base.

Given Conc of NH3= 0.321 M & NH4Cl = 0.123 M

pOH = pKb + log10 (BH+ / B )

pOH = 4.7447 + log(0.123 / 0.321 )
pOH = 4.7447 + log(0.3831) = 4.7447 – 0.4166

pOH = 4.33

We know PH + pOH =14

pH =14 – 4.33

pH = 9.67

 

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