study-note-6-63 - A chart with the Molar...

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What is often helpful when solving Ksp problems? A chart with the M olar ratios, [I nitial], [C hange], and [E quilibrium] of all products (as a mnemonic remember RICE, MICE, or ICE box). Since the reactant is a solid, it is ignored. PbF 2 (s) Pb 2+ (aq) F (aq) Mole ratio 1 2 [Initial] (M) 0 0 [Change] (M) + x + 2x You are told that the molar solubility of PbF 2 (s) is 2.15 x 10 –3 mol/L. Write the equilibrium chart that will assist you in calculating Ksp. [Equilibrium] (M) x (= 2.15x10 –3 ) 2x (= 4.30x10 –3 ) > solve for Ksp. Ksp = [Pb 2+ ][F ] 2 = [2.15x10 –3 ][4.30x10 –3 ] 2 = 3.98 x 10 –8 What is the common ion effect? When dissolving a solid in water, if one of the ions that the solid dissociates into is already present, less of the solid will dissolve. Explain the common ion effect using CaCl 2 (s) Ca 2+ (aq) + 2Cl (aq) as an example. By adding NaCl to this equilibrium, some CaCl 2 will come out of solution. (Or if the solution initially contains NaCl, less CaCl 2 will dissociate). Additional NaCl increases the concentration of Cl , shifting the equilibrium to the left (Le Chatelier’s principle).
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