Work Sheet 8+ CH302 Spring 2008 1. A solution is made with NaI and NaCl such that it is 0.01 M in both I- and Cl-. To 1 L of this solution 0.01 moles Ag(NO3) are added (you can ignore any volume change). The NaI, NaCl, and Ag(NO3) are completely soluble (as is NaNO3 but you already knew that). The KSP for AgI is 8.3 x 10-17 and for AgCl is 1.8 x10-10. After the solution has reached equilibrium what are the concentrations of the following? Will anything precipitate? Initial concentration of [Ag+] is 0.01 M, [I-] = 0.01 M, [Cl-] = 0.01 M Qsp = [Ag+][I-] = (.01)(.01) = 10-4 AgI could precipitate Qsp = [Ag+][Cl-] = (.01)(.01) = 10-4 AgCl could precipate However AgI is much less soluble than AgCl. Assume the AgI precipitates completely to equilibrium Then you have a saturated solution of AgI Concentration of Ag+ will be Ksp = [Ag+][I-] [Ag+] = sqrt(Ksp) = sqrt(8.3 x 10-17) = 9.11 x 10-9 Given this concentration will the AgCl precipitate? Qsp = [Ag+][Cl-] = (9.11 x 10-9)(.01) = 9.11 x 10-11 Qsp < Ksp so no AgCl will precipitate [Ag+] 9.11 x 10-9 M [I-] 9.11 x 10-9 M [Cl-] 0.01 M Are there any solid precipitates? If so how many grams of each. Only AgI will precipitate. Essentially all the silver will precipate as AgI. That is 0.01 moles. (0.01 mol)(234.8 g mol-1) = 2.35 g2. The Ksp of PbCl2 is 1.7 x 10-5. How many grams of PbCl2 will dissolve in 100 mL of a 0.1 M NaCl solution? Pb2+ Cl- I 0 .1 C +x +2x E +x .1+2x Ksp = [Pb2+][Cl-]2 = (x)(.1 + 2x)2 ~ (x)(.1)2 [Pb2+] = Ksp/[Cl-]2 = (1.7 x 10-5)/(.1)2 = 1.7 x 10-3 that will be (1.7 x 10-3 M)(.1 L) = 1.7 x 10-4 moles PbCl2 (1.7 x 10-4 moles)(278.1 g mol-1) = 0.047 g 3. Will CaF2 be more soluble in acid or base? F- is the conjugate base of the weak acid HF. In acid, F- will form HF allowing more CaF2 to dissolve. 4. Consider the following reactions AgCN(s) --- Ag+(aq) + CN-(aq) HCN (aq) --- H+(aq) + CN-(aq) You a saturated solution of AgCN, what will the effect of each of the following (nothing, more AgCN dissolves, some AgCN precipates) What is the concentration of A. Adding HNO3 Increasing H+ will cause more HCN to form lowering the CN- concentration. More AgCN will dissolve. (also the Cl- concentration will increase. If it get high enough AgCl will precipitate causing more AgCN to dissolve) B. Adding KCN Adding CN- will cause some AgCN to precipitateC. Adding KNO3 Adding K+ and NO3- will do nothing 5. A blast from the past ! AgBr(s) " Ag+(aq) + Br#(aq)Ag+(aq) + 2S2O32#(aq) " Ag(S2O3)23#(aq)S2O32#(aq) + H3O+(aq) " HS2O3#(aq) + H2O(l) What is the effect of each of these on the solubility of AgBr(s) 1. Adding the soluble salt Kbr This will decrease the solubility of the AgBr as the concentration of Br- will increase 2. Adding the soluble salt Na2S2O3 This increase the solubility of the AgBr. The S2O3- will react with the silver to form Ag(S2O3)23-. This will decrease the Ag+ concentration leading to more AgBr dissolving. 3. Adding HCl Adding HCl will casue the S2O32- to form HS2O3-. This will decrease in S2O32-. This will cause Ag(S2O3)3- to dissolve forming more Ag+. This will decrease the solubility of the AgBr 4. Adding solid AgBr This will have no
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