stoltzfus_chem123_Midterm1_page4

stoltzfus_chem123_Midterm1_page4 - (d) CuS, PbS, and SnS...

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12. [7 points] The Group II ions are precipitated from acidic solution as sulfides. The precipitating reagent is 5 % thioacetamide and heating to 80 ° C produces a saturated solution of hydrogen sulfide with the concentration of H 2 S being 0.10 M. Calculate the molar concentration of HS - in a solution that is saturated with H 2 S and made acidic with concentrated 0.3 M HNO 3 . H 2 S H + + HS - K 1 = 9.5 x 10 -8 HS - H + + S 2- K 2 = 1.0 x 10 -19 (a) 3 x 10 -8 (b) 3 x 10 -7 (c) 3 x 10 -6 (d) 3 x 10 -5 (e) 3 x 10 -4 13. [7 points] If the metal ion concentrations are estimated to be 0.01 M, which of the following sulfides would precipitate from the solution described in question 12? The K sp values shown below are determined from the following equation: MS(s) + H 2 O(l) M 2+ (aq) + HS - (aq) + OH - (aq) CoS 5.0 x 10 -22 PbS 3.0 x 10 -28 CuS 6.0 x 10 -37 SnS 1.0 x 10 -26 FeS 6.0 x 10 -19 (a) CuS only (b) CuS and PbS (c) CoS and FeS
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Unformatted text preview: (d) CuS, PbS, and SnS (e) CoS, CuS, FeS, PbS, and SnS A student was handed a test tube containing the following 12 cations in solution: Ag + , Pb 2+ , Bi 3+ , Cu 2+ , Sb 5+ , Sn 4+ , Fe 3+ , Al 3+ , Cr 3+ , Ni 2+ , Co 2+ , and Zn 2+ and performed the following analysis: 1. Cold, dilute HCl was added to the solution in the test tube forming a white precipitate and a clear decantate. The decantate was transferred to a clean dry test tube to be analyzed in step 2. 2. The decantate obtained in step 1 was treated with HNO 3 and H 2 S forming a dark precipitate and a colorless solution. The student again centrifuged and dumped the colorless decantate in a clean dry test tube for further analysis in step 3. 3. The solution obtained in step 2 was treated with NH 3 and NH 4 Cl forming a dark precipitate and a colored solution....
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This note was uploaded on 09/15/2008 for the course CHEM 123 taught by Professor Larosa during the Spring '06 term at Ohio State.

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