E2ps11key - CH302 Practice Exam 2Answer Key 1 If 500 ml of each of the following solutions is combined which will not produce a buffer a.1 M

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CH302 Practice Exam 2—Answer Key 1. If 500 ml of each of the following solutions is combined, which will not produce a buffer? a. .1 M trichloroacetic acid + .1 M sodium trichloroacetate b. .3 M trichloroacetic acid + .15 M barium hydroxide c. .3 M trichloroacetic acid + .2 M sodium hydroxide d. .2 M sodium trichloroacetate + .18 M hydrochloric acid Option b neutralizes to produce a weak base solution. 2. Consider the following table of acids and their pKa values. Rank these acids in order of increasing strength of their conjugate bases. Acid pKa CHOOH 3.77 CH 3 COOH 4.75 HF 3.20 a. HF < CH 3 COOH < CHOOH b. CHOOH < CH 3 COOH < HF c. CH 3 COOH < CHOOH < HF d. HF < CHOOH < CH 3 COOH The stronger an acid, the weaker its conjugate base. The lower the pK a , the stronger the acid. So, rank the acids in order of increasing pK a s. 3. What is the pH of a 100 mL of a buffer solution containing .25 M formic acid and .30 M sodium formate if you add .01 mols of Ba(OH) 2 ? The pKa of formic acid is 4. a. 3.7 b. 4 c. 4.4 d. 5 R HA + OH - --> A - I .025 .02 .03 C -.02 -.02 +.02 E .005 0 .05 [H + ] = 10 -4 (.005/.05) = 10 -5 pH = 4 4. Consider the following titration curve of an acid, H 2 A:
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a. H 2 A b. HA - c. A 2- d. No species is predominant, [H 2 A] = [HA - ] At the first equivalence point, all of H 2 A has been converted to HA - . 5. If 25 mL of a .17 M solution of barium hydroxide is titrated with 75 mL of a .1 M nitric acid solution, what is the final pH? a. 12 b. 1.5 c. 11 d. 7 R H+ + OH- --> H2O I .0075 .0085 ~ C -.0075 -.0075 ~ E 0 .001 ~ [OH-] = .001/.1 = 10-2 pOH = 2 pH = 12 6. A 100 mL solution of .25 M (CH 3 ) 3 NHCl is titrated with 80 mL of a .25 M solution of NaOH. What is the pH of the final solution? The pKa of (CH
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This note was uploaded on 09/17/2011 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas at Austin.

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E2ps11key - CH302 Practice Exam 2Answer Key 1 If 500 ml of each of the following solutions is combined which will not produce a buffer a.1 M

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