13. Which one of the following would be the best choice as an indicator in the t

Question

13. Which one of the following would be the best choice as an indicator in the titration of a 0.100 M ammonia solution (NH3) with a 0.100 M hydrochloric acid solution (HCI)? [a] thymol blue, Ka = 1.58x 10-9 a] thymol blue, Ka 1.58 x 10 9 [bl methyl orange, Ka - 1.58 x 10 4 [d] thymolphthalein, Ka 1.26 x 1010 cresol red, Ka 1.26 x 10-8 e] All indicators listed below would work equally well. 9) Consider a titration between a common weak acid (HA) titrated with the strong base (NaOH). The pH at the equivalence point is determined by what species in solution? b] NaOH [c] A [d] Na+ ,because ce poin acid/base titration at 25 C

Explanation / Answer

13.

the pKb = 4.75

so, in the neutralization

there is weak acid," NH4+" so

pH = pKb = 4.75

then, choose a color nearest to that pKb value, i.e methyl orange will be a very good option since it is low ins Ka

9.

the pH of the equivalence point must be determined essentially due to

A- conjguate base

since

HA + OH -- > H2O + A-

A- + H2O <--> HA + OH-

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