e2ps10key

# e2ps10key - 1 What is the pH of a 1 L solution made with...

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1. What is the pH of a 1 L solution made with 3.26 g of trichloroacetic acid and 37.0 g of sodium trichloroacetate? The K b of sodium trichloroacetate is 10 -12 . Molecular weights of tichloroacetic acid and sodium trichloroacetate are 163 g/mol and 185 g/mol respectively. a. 4 b. 3.5 c. 3 d. 2 mols of acid = 3.26/163 = .02 mols of base = 37.0/185 = .2 pK a = pK w - pK b = 14 - 12 = 2 K a = 10 -2 [H + ] = 10 -2 (.02/.2) = 10 -2 * 10 -1 = 10 -3 pH = -log(10 -3 ) = 3 2. 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. 3. Consider the following table of acids and their pK a values. Rank these acids in order of increasing strength of their conjugate bases. Acid pK a CHOOH 3.77 CH 3 COOH 4.75 HF 3.20 a. HF < CH3COOH < CHOOH b. CHOOH < CH3COOH < HF c. CH3COOH < CHOOH < HF d. HF < CHOOH < CH3COOH 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 pKas. 4. What volume of 1 M calcium hydroxide could be added to 500 mL of a buffer that is 0.4 M ammonia and 0.6 M ammonium chloride before exhausting the buffer? a. 600 mL b. 300 mL c. 150 mL d. 400 mL e. 200 mL When a strong base such as Ca(OH) 2 is added to a buffer, it will react with the acidic species, in this case ammonium. The buffer contains 0.3 moles of ammonium, and this will be exhausted by 150 mL of calcium hydroxide. 5. 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 -

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I .025 .02 .03 C -.02 -.02 +.02 E .005 0 .05 [H + ] = 10 -4 (.005/.05) = 10 -5 pH = 5 6. Consider the following titration curve of an acid, H 2 A: At the point indicated by the arrow, which species is predominant? 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 H2A has been converted to HA - . 7. If 25 mL of a .17 M solution of barium hydroxide is titrated with 75 mL of a .1 M nitric
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## This note was uploaded on 09/12/2010 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas.

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e2ps10key - 1 What is the pH of a 1 L solution made with...

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