q4ps11key - CH302 Practice Quiz 4 TA StyleAnswer Key 1 What...

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CH302 Practice Quiz 4 TA Style—Answer Key 1. What is the molar solubility of Be(OH) 2 in a solution with a pOH of 2? The Ksp of Be(OH) 2 is 7x10 -22 . a. 7x10 -24 b. 7x10 -18 c. 7x10 -20 d. 7x10 -22 A pOH of 2 corresponds to [OH-] of 0.01, and OH- is our common ion. Ksp = [Be 2+ ][OH - ] 2 7x10 -22 = x(0.01 + 2x) 2 , assuming that 2x is small relative to 0.01 7x10 -22 = x(0.01) 2 x = 7x10 -18 2. Which of the following cations would be hardest to separate by addition of OH - ? Be(OH) 2 K sp = 7x10 -20 Co(OH) 2 K sp = 6x10 -15 Ca(OH) 2 K sp = 5x10 -6 Mg(OH) 2 K sp = 5.6x10 -12 a. Be 2+ and Co 2+ b. Co 2+ and Mg 2+ c. Mg 2+ and Ca 2+ d. Be 2+ and Ca 2+ Since all of the salts are of the form MX 2 , a single divalent cation and 2 hydroxide anions, all of the K sp s can be directly compared. The two most difficult to separate metal ions will be the two with the closest K sp s. In this problem, that is Co 2+ and Mg 2+ , whose Ksps differ by only 3 orders of magnitude, approximately. 3. Write the correct charge balance for an aqueous solution of BaSO
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This note was uploaded on 09/17/2011 for the course CH 302 taught by Professor Holcombe during the Spring '07 term at University of Texas.

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q4ps11key - CH302 Practice Quiz 4 TA StyleAnswer Key 1 What...

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