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In: Chemistry

The Kb of NH3 at some temperature is 4.54 x 10-5. What is the pH of...

The Kb of NH3 at some temperature is 4.54 x 10-5. What is the pH of a solution prepared by combining 34.26 mL of 1.94 M NH3(aq) and 50.0 mL of 1.00 M NH4NO3 (aq) at that temperature?

Expert Solution

Concentration of [NH3] in solution = 1.94 M x 34.26 ml/84.26 ml

= 0.80 M

Concentration of [NH4NO3] in solution = 1.00 M x 50 ml/84.26 ml

= 0.59 M

This is a buffer solution of weak base NH3 and its conjugate acid NH4NO3

So using Hendersen-Hasselbalck equation,

pH = pKa + log(base.acid)

where,

pKa = 14 - pKb

with,

pKb = -log[Kb]

= -log(4.54 x 10^-5)

= 4.343

So,

pKa = 14 - 4.343 = 9.66

Thus, pH of this solution would be,

pH = 9.66 + log(0.80/0.59)

= 9.79

queen_honey_blossom answered 2 years ago

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