8.To the nearest tenth, what is the pH of a 1.0 M solution of trifluoroacetic ac

Question

8.To the nearest tenth, what is the pH of a 1.0 M solution of trifluoroacetic acid (CF3CO2H) with a pKa = 0.2? a. 0.9 b. 0.7 c. 0.5 d. 0.3 e. not a.-d.

9. Given that for aspirin pKow = -1.2, starting with 1 gram (two extra-strength tablets) of aspiring in 8 ounces (a cup) of water, to the nearest tenth of a gram, how much aspiring is extracted into a tablespoon (1/2 an ounce) of octan-1-ol? a. 0.9 b. 0.7 c. 0.5 d. 0.3 e. not a.-d.

11. Knowing which way the equilibrium is favored, which oxygen of question 10 is the strongest nucleophile? a. Oe b. Od c. Oc d. Ob e. Oa

Explanation / Answer

Q8.

CF3CO2H is a weak acid so

CF3CO2H <-> CF3CO2- + H+

Ka = [CF3CO2-][H+]/[CF3CO2H]

so

Ka = 10^-pKa = 10^-0.2 = 0.63095

in equilibrium:

[CF3CO2-]= x

[H+] = x

[CF3CO2H] = M-x = 1 -x

substitute

Ka = [CF3CO2-][H+]/[CF3CO2H]

0.63095 = x*x/(1-x)

x^2 + 0.63095x -1*0.63095 = 0

x = 0.5392

therefore

[H+] = x = 0.5392

so

the pH = -log(0.5392) =0.26825

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