1306 Exam III Spring 2016 Print Name (Legibly) Student ID Number: (Last) (First)

Question

1306 Exam III Spring 2016 Print Name (Legibly) Student ID Number: (Last) (First) A. (16 points). how tini Show how you do the calculation and then determine the pH when 200. mL of 0.15 M HCI ml. of 0.26 M NaAc (sodium acetate). For acetic acid. K-1.8x 10 is mixed with 400. B. (24 points) Consider the reaction in aclosed container 2 sotg) 0; (g) + 2 SO, (g) Suppose at time zero there are no SO, molecules and the stated products both start at 4.0 M. i.e. [O: (g). -ISO, (g)). 4.0 M. The reaction proceeds to equilibrium. Sketch reasonable curves as a function of time for the concentrations for all species in the reaction if the equilibrium constant, K, - K for this reaction is 3.0. Show concentrations versus time based on the data (show your calculation, ie. show how you arrived at your answer for an of value 3.0). The concentration axis should be linear- show in lv

Explanation / Answer

Question 1

this is a buffer

mmol of acid = MV = 200*0.15 = 30

mmol of acetate = 0.26*400 = 104

after reaction

mmol of acetic aicd formed = 30

mmol of acetate left = 104-30 = 74

this is a buffer so

pH = pKa + log(acetate/Acid)

pH = 4.75 + log(74/30) = 5.14

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