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HW3_31

# HW3_31 - 2 Cl 1(Note the Cl 1-is a spectator ion in this...

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Homework due 3/31 Calculate the pH at which Co(OH) 2 will start to precipitate from a solution that is 0.010 M in CoCl 2 . (K sp Co(OH) 2 = 2.2x10 -20 ) To solve this problem one first needs to calculate the maximum allowable OH 1- concentration, before precipitation will take place, i.e. the case where the Q sp = K sp . Form this one can then determine the pH and the pOH of the solution. CoCl 2 Co 2+
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Unformatted text preview: + 2 Cl 1- (Note: the Cl 1-is a spectator ion in this problem.) Co(OH) 2 Co 2+ + 2 OH 1-Ksp = [Co 2+ ][OH 1-] 2 Since the CoCl 2 ionizes completely to give 1 mole of Co 2+ /1 mole CoCl 2 the [Co 2+ ] = 0.010 M. Thus, K sp = [Co 2+ ][OH 1-] 2 = (0.010)[OH 1-] 2 = 2.2x10-20 [OH 1-] = 1.48x10-9 pOH = -log[OH 1-] = 8.83 pH = 14 - pOH = 14 - 8.83 = 5.17...
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