In the laboratory, you have been studying various ways to separate and identify
ID: 822260 • Letter: I
Question
In the laboratory, you have been studying various ways to separate and identify the cations present in a mixture. In one portion of the separation scheme, the separation of Fe3+ and Ni2+ is brought about by adding both NH3 and NH4+ to the mixture to create a buffer and control [OH-]. The procedure calls for the addition of 0.5 mL of 1 M NH3 and 1 ml of 1M NH4Cl. What will be the pH of this buffer solution?
if you could give me a step by step that would be great. I dont really just want an answer I want to understand how to do it.
Explanation / Answer
NH3 + NH4Cl
NH4Cl = NH4+ + Cl-
NH3 is a weak base with Kb of 1.8 x 10^-5
conectration of NH3 = moles of NH3/ total volume = 0.5x1/1.5 = 1/3
conectration of NH4+ = moles of NH4+/ total volume = 1x1/1.5 = 2/3
NH3 + H2O = NH4+ + OH-
pOH = pKb + log[NH4+]/[NH3]
pOH = 4.74 + log(2/3)/(1/3)
pOH = 4.74 + 0.3
pOH = 5.04
pH = 14 - pOH = 14-5.04
pH = 8.95 ans
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