Question

Calculate the pH of the following aqueous solution: 0.37 M NH4Cl (pKb for NH3 = 4.74)

Answer 1

Calculate the pH of the following aqueous solution: 0.37 M NH4Cl (pKb for NH3 = 4.74)

Ammonium chloride is a salt of Weak base(NH3) and strong acid (HCl)

In aqueous medium the hydrolysis of NH4Cl is given as,

NH4Cl + H2O < --------- > NH4⁺ + Cl^-

NH4⁺ + HO-H < ------- > NH4OH + H⁺

Because of this the aqueous solution of NH4Cl is acidic.

For aqueous solution of weak base-strong acid pH is given as,

pH = 7 – ½(pKb)- ½ (log[salt])

We have, pKb = 4.74, [salt] =[NH4Cl] = 0.37 M

So, pH = 7 – ½(4.74)- ½ log[0.37]

pH = 7 – 2.37 – ½ (0.432)

pH = 4.63 – 0.216

pH = 4.414.

pH of aq. 0.37 M NH4Cl solution is 4.414.

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