6 Using the method that we learned in class to estimate specific gravities and g

Question

6 Using the method that we learned in class to estimate specific gravities and given the following atomic weights (C 12, H 1. N 14. o 6), which compound has a density closest to that of water? 7. Compound 6 a. will? sink in water b make an emulsion with water d, dissolve in water float on water e, not a -d 8. Given that for aspirin pKew 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-l ol e, not a, d d, 0.3 a, 0.9 b, 0,7 c, 0,5 9. To the nearest tenth, what is the pH ofa 1.0 M solution of trifuoroacetic acid (CFyCO2H) with a pK. 0.2? d, 0,3 e, not a, d, b, 0,7 a. 0.9 c, 0,5 10, Given (from left to righ) the pKas of salicylic acid (aspiring precursor), sodium bicarbonate, sodium salicylate, and carbonic acid; use the correct pKas to determine the concentration of carbonic acid produced (to the nearest hundredth) from 1.0 M concentrations of both starting materials. The subscripts on the oxygens are for the next question d, 0.99 e, not a, d c, 0.97 b, 0.95 a, 0,93 11. Knowing which way the equilibrium is favored, which oxygen of question 10 is the strongest nucleophile? Na d, Od

Explanation / Answer

9. pKa of trifluoroacetic acid (CF3COOH) is 0.2; therefore, Ka = antilog (-0.2) [Pka = -log (Ka)]

===> Ka = 0.631

Write down the dissociation of CF3COOH as

CF3COOH (aq) <=====> H+ (aq) + CF3COO- (aq)

Ka = [H+][CF3COO-]/[CF3COOH] = (x).(x)/(1.0 – x)

===> 0.693 = x2/(1.0 – x)

Since Ka is small, x is much smaller than 1.0; hence write

0.693 = x2/1.0

===> x2= 0.693*1.0 = 0.693

===> x = 0.832

Therefore, [H+] = 0.832 M and pH = -log [H+] = -log (0.832) = 0.0798 0.08 (ans).

Ans: (e) not a-d

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