You have a summer job as an intern in an analytical chemistry laboratory. You ar

Question

You have a summer job as an intern in an analytical chemistry laboratory. You are about to titrate a solution of nicotine (pK_s = 6 0). which is a base similar to ammonia, with a standard hydrochloric acid solution. Two pH indicators are available for you to use thymol blue (pK_a = 3.47) and phenolphthalein (pk_b = 9.4). Which indicator do you select as being the more appropriate one to use? a Both indicators would work equally well because at the equivalence point the pll of the solution changes very sharply from strongly bask to strongly acidic, b. Phenolphthalein is the better choice because it is one of the most commonly used pH indicators. C. Neither of these indicators would work because their pA, values are not close to 7.00. which is the pH of the solution at the espies alliance point, d Phenolphthalein is the better choice because the sample pH at the equivalence point will be close to the pK, value of 9.4. e Thymol blue is the better choice because the sample pH at the equivalence point will be close to the pA. value of 3.47. In a titration of monoprotic acids and bases, there is a large change in pH____ a. at the point where pH = pA, of the acid. b. when the volume of acid is exactly equal to the volume of base. c. w hen the concentration of acid is exactly equal to the concentration of base. d. when the number of moles of acid is exactly equal to the number of moles of base, c. at the point where pH - pK_b of the base. When an acetic acid solution is titrated with sodium hydroxide, the slope of the titration curve (pH versus volume of NaOH added) increases when sodium hydroxide is first added. This change shows that a. nothing is happening during this pan of the titration. b. the reaction is very slow during this part of the titration. c. a more concentrated solution of NaOH needs to be present to initiate the reaction. d. acetic acid is being converted to sodium acetate. e. the pH is not affected until all the acetic acid is consumed. Halfway to the equivalence point in a titration curve of a weak acid with a strong base. ____ a. nothing is happening yet. d. pH = pK_a of the indicator. b. the pH = pK_a, of the weak acid. c. the pH has not vet changed. c. pH = 3.5 exactly.

Explanation / Answer

Answer:-

10.

e. Thymol blue is the better choice because the sample pH at the equivalence point will be close to the pKa value of 3.47 .

11.

d. when the number of moles of acid is exactly equal to the number of moles of base.

12.

d. acetic acid is being converted to sodium acetate.

13.

b. The pH = pKa of the weak acid.

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