Question

Design a buffer that has a pH of 4.77 using one of the weak acid/conjugate base systems shown below.

Weak Acid	Conjugate Base	Ka	pKa
HC2O4-	C2O42-	6.4×10-5	4.19
H2PO4-	HPO42-	6.2×10-8	7.21
HCO3-	CO32-	4.8×10-11	10.32

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 =  g

grams potassium salt of conjugate base =  g

Design a buffer that has a pH of 4.77 using one of the weak acid/conjugate base systems shown below. pka 6.4x10-5 4.19 Weak Acid HC204 H2PO4 HCO3" Conjugate Base C2042 HPO42- CO32- 7.21 6.2x10-8 4.8x10-11 10.32 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 = ol grams potassium salt of conjugate base = 09

Answer 1

Since the given pH (4.77) is nearer to ionization of HC2042 The buffer must be prepared by HC204- (acid component) and C204-2(base component) pH = pK, + log [base] *[acid] >> 4.77 = 4.19+log 1930 1 [HC0,-) log [C,0,?] -0.58 10% [HC,0,-) [C204] -100.58 = 3.801894 [HC,0,-) Given that conc. of weak base = 1.00 M that is [C,0,?]=1.00M [HC,0,-1- [90,?] 1.0M -= 0.263027M 3.801894 3.801894 [HC,0,-]=0.263027M [0,0,?]=1.0M Volume of the buffer solution = 1.00 L Number of moles of [HC,0,-) present in the solution = M*V = 0.263027Mx1.00 L = 0.263027 mol Number of moles of [C,0,?] present in the solution = M*V =1.00Mx1.00 L = 1 mol mass of [KHCO,]=moles x mol.wt. =0.263027 molx128.13 g/mol = 33.70 g mass of [K,CO,]=moles x mol.wt. =1 molx166.22 g/mol = 166.22 g potassium salt of weak acid = 33.70 g potassium salt of conjugate base=166.22 g 0 =