A buffer of pH 4.1 is to be prepared from a weak acid and its salt. The best aci
ID: 1050130 • Letter: A
Question
A buffer of pH 4.1 is to be prepared from a weak acid and its salt. The best acid from which to prepare the buffer is phthalic acid, K_1 = 1.3 times 10^-3 (first ionization) hydrogen phthalate, K_1 = 3.9 times 10^-5 (second ionization of phthalic acid) benzoic acid, K = 6.3 times 10^-5 hydrocyanic acid, K = 4 times 10^-10 The addition of solid Na_2SO_4 to an aqueous solution in equilibrium with solid BaSo_4 will cause no change in [Ba^2+] in solution. more BaSO_4 to dissolve. precipitation of more BaSO_4. an increase in the K_sp of BaSO_4. The solubility of silver acetate, AgC_2H_3O_2, is 1.02 g per 100 mL. What is the K_sp? 3.7 times 10^-5 1.0 times 10^-4 2.8 times 10^-4 3.7 times 10^-3Explanation / Answer
29. The pKa should be close to pH needed for the buffer to be prepared.
Thus for a buffer with pH 4.1, we would use,
(C) benzoic acid (pKa 4.2)
30. The addition of Na2SO4 to BaSO4 will cause more of BaSO4 to form, by common ion effect according to LeChatellier's principle,
BaSO4(s) <==>Ba2+(aq) + SO4^2-(aq)
(C) precipitation of more BaSO4
31. With solubility of AgC2H3O2 = 1.02 g/167 g/mol x 0.1 L = 0.0611 M
Ksp = [Ag+][C2H3O2-] = (0.0611)^2 = 3.7 x 10^-3
(D) 3.7 x 10^-3
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