Chp7_TitrnProb

# Chp7_TitrnProb - Consider a 0.168 M aqueous solution of a...

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Consider a 0.168 M aqueous solution of a monoprotic weak acid, HA, characterized by an acid- dissociation constant, Ka = 3.9e-9. A 25.0 mL aliquot of this solution is titrated with 0.0945M NaOH. a. Calculate the initial pH of the analyte solution; b. Determine the volume (in mL) of base needed to reach the endpoint; c. Determine the pH at the endpoint; d. Determine the pH after the addition of 10.4 mL of titrant; e. Determine the pH after the addition of 54.4 mL of titrant; f. Determine the pH in the limit of a large excess of titrant. (a) Initial pH. At this point, we have 25 mL of a weak acid solution. We know from previous work: x c x K a - = 0 2 where x is the [H 3 O 1+ ] Thus: x x - = × - 168 . 0 10 9 . 3 2 9 ( 29 ( 29 o C x << × = × - - 5 9 10 56 . 2 168 . 0 10 9 . 3 pH = 4.59 (b) At endpoint the number of moles of titrant (base) = number of moles of analyte (acid) ( 29 ( 29 mL M M mL V C V C V T A A T T 4 . 44 0945 . 0 168

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Chp7_TitrnProb - Consider a 0.168 M aqueous solution of a...

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