HW 3 Solutions

# HW 3 Solutions - 53:050 Natural Environmental Systems...

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53:050 Natural Environmental Systems Solutions to Homework No. 3 – Spring 2011 1. What are the molar concentrations of H + and OH - in a solution with pH = 7.7? Use equations 2-36 and 2-37 and assume T = 25 o C. pH = -log[H + ] so, [H + ] = 10 -pH = 10 -7.7 = 2.00 x 10 -8 [OH - ] = ] [H K w + = 8 - -14 10 x 2.00 10 = 5.00 x 10 -7 2. instead of HCl, add 200 mg of HNO 3 . Assume T = 25 o C. TOT NO 3 = /mol HNO mg 63,000 L / HNO mg 200 3 3 = 3.17 x 10 -3 M HNO 3 is a strong acid. Thus, it completely dissociates when added to water as we discussed in class. This means [NO 3 - ] = 3.17 x 10 -3 M. So, from the charge balance: [H + ] = [OH - ] + [NO 3 - ] [NO 3 - ] = 3.17 x 10 -3 M pH = -log(3.17 x 10 -3 ) = 2.50 3. instead of sodium acetate, add 11. 1 g of sodium propionate (CH 3 CH 2 COONa). The pK a of propionic acid (CH 3 CH 2 COOH) is 4.89 at 25 o C. TOT

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## This note was uploaded on 06/03/2011 for the course 53 50 taught by Professor Parkin during the Spring '11 term at University of Iowa.

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HW 3 Solutions - 53:050 Natural Environmental Systems...

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