Hi Genius! Please answer all parts: Buffers ;-) a) Which of the following acids
ID: 902736 • Letter: H
Question
Hi Genius!
Please answer all parts:
Buffers ;-)
a) Which of the following acids would be most suitable for preparing a buffer of pH = 3.50?
PIPES (Piperazine- N,N’- bis (2-ethanesuflonic acid) pKa = 2.67
Citric Acid pKa = 3.13
Glycylglycine pKa = 3.14
PIPPS (Piperazine –N,N’ – bis(3-propoanesulfonic acid) pKa = 3.79
PIPBS (Piperazine-N,N’- bis (4-butanesulfonic acid) pKa = 4.29
b) Which of the following bases would be most suitable for preparing a buffer of pH 9.00?
Ammonia Kb = 1.76 x 10 -5
Aniline Kb = 3.99 x 10-10
Hydrazine Kb = 1.05 x 10-6
Pyridine Kb = 1.58 x 10-9
c) Calculate the pH of a buffer solution prepared by mixing 0.0400 moles of ammonia with 0.0600 moles of ammonium chloride in 1.00 L of water? pKb = 4.75
d) Consider the titration of the weak Acid HA with NaOH. At what fraction of the Ve does the pH = PKa – 1 if the concentration of HA=Aninilinium bromide is 0.100 M and NaOH is 0.100 M?
e) What is the maximum buffer capacity?
f) At What point in the titration of a weak base with a strong acid is the maximum buffer capacity is reached?
Thanks in advance!
Explanation / Answer
a) Which of the following acids would be most suitable for preparing a buffer of pH = 3.50?
You should choose any substance with a pKa = 3.5
Best acid that will suit the buffer is
PIPPS (Piperazine –N,N’ – bis(3-propoanesulfonic acid) pKa = 3.79
b) Which of the following bases would be most suitable for preparing a buffer of pH 9.00?
if you want pH = 9 then pOH = 14-9 = 5
choose any pKb near 5, that is 10^-5
NH3, ammonia will be a goof buffer, since pKb = 4.75
c) Calculate the pH of a buffer solution prepared by mixing 0.0400 moles of ammonia with 0.0600 moles of ammonium chloride in 1.00 L of water? pKb = 4.75
n = 0.04 mol of NH3
n = 0.06 mol of NH4Cl
V = 1 L therefore, all other moles may be considered as concnetration as well
pOH = pKb + log(HB+/B)
pOH = 4.75+log(0.06/0.04) = 4.93
pH = 14-pOH = 14-4.93 = 9.07
d) Consider the titration of the weak Acid HA with NaOH. At what fraction of the Ve does the pH = PKa – 1 if the concentration of HA=Aninilinium bromide is 0.100 M and NaOH is 0.100 M?
the fraciton will be 1:1 since moralirites are the same 1:1
C = (10*[HA] - [A-] )/ 11
Capacity = 10(0.1)-0.1) / 11 = 0.08
f) pH = pKa +/- 0.08