Homework Answers
1. Kb of NH3 = 1.8 * 10-5 .
pKb of NH3 = -log(Kb) = - log (1.8 * 10-5) = 4.74
pKa + pKb = 14
So pKa = 14 - 4.74 = 9.26
A buffer works best within a pH range of + or - pKa.
So ammonia buffer works best in pH = 9.
2. Gas molecules always have a higher entropy than solids or gases as they are more disordered. We can see the reaction proceeds from a gaseous state to a solid state. Thus there is decrease in disorderliness of the system. So delta S for this reaction will be negative.
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