ma Recitation Quiz 6- 2011-1-1

ma Recitation Quiz 6- 2011-1-1 - Chemistry 106 Recitation...

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Chemistry 106 Recitation 2-24 Name: Section: 1. (2 points) Which of the following compounds dissolve in water? (Circle if soluble) Na 2 CO 3 CaCO 3 CaS NH 4 S PbSO 4 Cd(OH) 2 NaCl 2. (2 points) What is the solubility of cadmium hydroxide? K sp = 2.5 × 10 -14 K sp =[Cd 2+ ][OH - ] 2 Cd(OH) 2 Cd 2+ + 2OH - I ------ 0 0 C ------- +x +2x E ------- x 2x K sp =[x][2x] 2 =4x 3 . . . simplify . . . 2.5E-14 = 4x 3 then [(2.5 E-14)/4)] 1/3 = x = 1.842E-5 Because ICE tables are in concentration, the x we just solved for was in moles/L. To get to just solubility instead of molar solubility we multiply by the molecular weight of Cd(OH) 2 which is 146 grams/mole. 1.842 E-5 mole Cd(OH) 2 x 146 grams = .00269 grams Liter mole Cd(OH) 2 Liter 3. (2 points) What is the solubility of cadmium hydroxide if it is placed in a solution with an constant pH of 8.2 ? Because it is a buffer that means that the pH will not change ie the [OH] and [H + ] in solution will not change. The means the we use the pH=8.2 to find
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ma Recitation Quiz 6- 2011-1-1 - Chemistry 106 Recitation...

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