PS6_2011

# PS6_2011 - Name Section Rec TA Side 1 of 4 Ch 1b, Problem...

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Name Ch 1b, Problem Set Six Section Side 1 of 4 Due Friday, Feb. 18, 2011 Rec TA at 4 PM PST in the Drop Box 1. Buffer Solutions (21 points) An aqueous buffer is prepared by dissolving 0.13 mol of sodium sulfanilate (NaNH 2 C 6 H 4 SO 3 ) into 1.00 L of 0.20 M sulfanilic acid (NH 2 C 6 H 4 SO 3 H; K a =5.9x10 -4 ) at 25 ° C. (a) Calculate the pH of the buffer solution at equilibrium. (b) Suppose 0.040 mol of HCl is added to the buffer. Calculate the pH of the resulting solution. (c) Briefly describe two changes you could make to improve the capacity of the buffer solution described in the problem statement, without changing the chemicals used to make the buffer. (Note: Buffer capacity is defined as the number of moles of strong acid, or strong base, needed to change the pH of one liter of buffer solution by 1 pH unit.) (d) A good rule of thumb is that “The useful pH range of a buffer is usually considered to be pK a ± 1 pH unit.” Using this statement, determine the range through which the ratio of the concentration of the acid to the concentration of the conjugate base is most effective. 2. More pH Calculations (20 points) In this problem, you will consider a system containing two weak acids. Calculate the pH of a solution at 25 ° C that is prepared by dissolving 0.23 mol of hydrofluoric acid (HF) and 0.57 mol of hypochlorous acid (HClO) in water and diluting to 3.60 L. 3. Reversible Work: Fuel Cells vs. Heat Engines (20 points)

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## This note was uploaded on 03/21/2011 for the course CHEMISTRY 1b taught by Professor Reisman;heath during the Winter '11 term at Caltech.

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PS6_2011 - Name Section Rec TA Side 1 of 4 Ch 1b, Problem...

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