stoltzfus_chem123_Midterm1_page5

stoltzfus_chem123_Midterm1_page5 - and CoS as solids. (e)...

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14. [7 points] Which cations are present in the dark precipitate formed in step 3? (a) Al 3+ , Cr 3+ , and Fe 3+ (b) Ni 2+ , Co 2+ , and Zn 2+ (c) only Fe 3+ (d) Co 2+ and Ni 2+ (e) Fe 2+ and Cr 3+ 15. [7 points] What is the identity of the colored solution formed in step 3? (a) Al 3+ , Cr 3+ , and Fe 3+ (b) Ni 2+ , Co 2+ , and Zn 2+ (c) only Fe 3+ (d) Co 2+ and Ni 2+ (e) Fe 3+ and Cr 3+ 16. [7 points] How is Zn 2+ isolated from a mixture containing ZnS(s), NiS(s), and CoS(s)? (a) ZnS dissolves when concentrated NH 3 is added to form the Zn(NH 3 ) 4 2+ complex ion. (b) The solution is made to be distinctly acidic by adding concentrated HCl, which dissolves the ZnS and leaves the NiS and CoS as solids. (c) Due to the large difference in K sp values, dilute NaOH is carefully added to make the solution slightly basic, which dissolves the ZnS and leaves the NiS and CoS as a solid. (d) Ice cold 1 M HCl is added, which dissolves the ZnS and leaves the NiS
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Unformatted text preview: and CoS as solids. (e) Aqua regia is used because it will dissolve the ZnS and leave the NiS and CoS as solids. 17. [7 points] A solution contains 0.015 M Al 3+ and 0.015 M Ag + . Solid Na 3 PO 4 is slowly added to separate the two cations. The K sp for AlPO 4 is 9.8 x 10-21 and K sp for Ag 3 PO 4 is 8.9 x 10-17 . Which precipitate will form first and what concentration of PO 4 3- ion should be added to the solution to ensure the best separation? (a) AlPO 4 will form first; [PO 4 3-] = 6.4 x 10-19 M (b) AlPO 4 will form first; [PO 4 3-] = 2.5 x 10-11 M (c) Ag 3 PO 4 will form first; [PO 4 3-] = 6.4 x 10-19 M (d) Ag 3 PO 4 will form first; [PO 4 3-] = 2.5 x 10-11 M (e) a ppt will not form since solid Na 3 PO 4 is added...
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