Prepare a buffer by direct addition. Consider how best to prepare one liter of a
ID: 1028221 • Letter: P
Question
Prepare a buffer by direct addition. Consider how best to prepare one liter of a buffer solution with pH-7.72 using one of the weak acid/ conjugate base systems shown here. Weak Acid Conjugate BaseK C,0,2 HPO 62x10 co pk. 64 x 104.19 7.21 48 x 10 10.32 HC 04 HCOs How many grams of the potassium salt of the weak acid must be combined with how many grams of the potassium salt of its conjugate base, to produce 1.00 L of a buffer that is 1.00 M in the weak base? grams potassium salt of weak acid- grams potassium salt of conjugate base-Explanation / Answer
Given that:
pH = 7.72
pKa of H2PO42-= 7.21
H2PO4- + HPO4-2 mixture can act as best buffer , Because its pKa value nearer to its pH value.
pH = pKa + log [K2HPO4 / KH2PO4]
7.72 = 7.21 + log [K2HPO4 / KH2PO4]
log [K2HPO4 / KH2PO4]=0.51
[K2HPO4 / KH2PO4] = 3.24
1 / KH2PO4 = 3.24
KH2PO4 = 0.31 moles
KH2PO4 = 0.31 x 136.086 = 42.2 g
grams Potassium salt of weak acid = 42.2 g
K2HPO4 = 1 x 174.2= 174.2g
grams poatssium salt of conjugate base = 174 g