Question

"Acid-base buffers are most effective when the target pH of the buffer solution is close (within one unit) to the pKa of the conjugate acid in in the conjugate acid/base pair to be used in the buffer. This is called the buffer range for a particular acid/base system. For the three questions below, select the two compounds from the list which could be most effectively combined to create a buffer at the target pH. You will not need to use all of the compounds - and should need to use each compound only once.: 1. pH 4 buffer 2. pH 7 buffer 3. pH 9 buffer sodium acetate, Na(CH3COO)
	pyridinium chloride, (C5H5NH)Cℓ
	ammonium chloride, (NH4)Cℓ
	ammonia, NH3
	pyridine, C5H5N
	formic acid, HCOOH
	sodium formate, Na(HCOO)
	hypochlorous acid, HCℓO
	sodium hypochlorite, NaCℓO -Please provide explanation with answer if possible :)

Answer 1

pyridinium chloride, (C5H5NH)Cℓ --> pKa = 8.75

ammonium chloride, (NH4)Cℓ --> pKa = 4.75

ammonia, NH3 --> pKa = 9.25

pyridine, C5H5N --> 5.25

formic acid, HCOOH --> pKa = 3.75

sodium formate, Na(HCOO) --> pKa = 10.25

hypochlorous acid, HCℓO --> pKa = 7.5

sodium hypochlorite, NaCℓO --> pKa = 14-7.5 = 6.5

now, compare:

1. pH 4 buffer -> pKa = 4 -->

ammonium chloride, (NH4)Cℓ --> pKa = 4.75

formic acid, HCOOH --> pKa = 3.75

2. pH 7 buffer -> pKa = 7

hypochlorous acid, HCℓO --> pKa = 7.5

sodium hypochlorite, NaCℓO --> pKa = 14-7.5 = 6.5

3. pH 9 buffer pKa = 9

pyridinium chloride, (C5H5NH)Cℓ --> pKa = 8.75

ammonia, NH3 --> pKa = 9.25