A Short Qualitative Analysis Scheme without Hazardous Wastes John T. Petty\' Lon

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A Short Qualitative Analysis Scheme without Hazardous Wastes John T. Petty' Longwood College, Farmville, VA 23901 Most people who teach introductory chemistry would agree that actual laboratory experience is separation of lon Groups One of for helping the student u chemistry. 1. Place mLof known in a medium test tube. the best ways to introduce the student to some ofthe 2. Add 2 drops el 6 M HNO, then 1 ml of6MNHOH and stir. diverse behavior ofthe various elementa is through the use Centrifuge and decant the solution, to obtain solid A. a qualitative 3 To the remaining solution, add 2 1 M (NH The scheme safe mL of solid B. is virtually and fail solution and stir. Centrifuge and decant to give in more modern era it has flaws that A white reduce its utility. Many ofits ions and reagents are toxic or inogenic or form hazardous wastes. Proper collection 6 Test the ining solution for the Group C ions. and disposal of these wastes can even more Analysis of the Groups of Mons expensive than buying the reagents themselves. An Group A (AP, Mn' native was sou that would ght type of experience as the scheme sion into separations, clear testa) without its 1. Add 1 ml of the 1 M NaoH to the solid and stir vigorously accompanying problems in handling or disposal. with a glass stirring rod. Centrifuge and decant. ions initially chosen were limited to aluminum, the alkali the first-row elements Even 2 To the solution, add 2 MAcetie Acid dropwise until slightly acidie. A white precipitate indicates alumi a To the solid from step 1, add 2 add 6 MHNo, among this limited set ofions, several had to be eliminated until acidic. Divide the solution into two test tubes. from the scheme. Either their wastes could not be 4. To one test tube add a spatula tip of KSCN and stir until it all they difficult to separate and identify dissolves. A dark-red solution indicates iron. the presence of the ions. Aner much testing work modifications the following scheme was fo to for ions listed. the a spatula tip of KBio, stir vigorously for 30 s, and centrifuge A purple solution indieates color of the solution will iade on standing reacts in the air. as it Experimental Group B (Ba2 ca Analysis ofAP". Baa", ca ",Coa ,cuz ,Fea Mga Mna. ndd ml water to the and then slowly add a solution of 6 M HCI dropwise, until the has Preparation of Metal lon Test solutions and Unknowns 1 str. A white preeipitate, Solutions and unknowns were prepared aa shown in the indicates barium. Centrifuge and decant. mLofo the solution from step 2 add 3 drops of6 M NHOH and 1 The M NH for 1min. formation of a white precipitate indicates calcuim. table. Each of these solutions yields a ooneentration of about 10 mg mL of the metal ion, except Ba at 3 mgrmla Chloride salts may be used if some of the nitrates are unavailable, but they should be avoided as much as possi- CT reacts with some of the reagents used in the Group C (Co2, cu2., Ni2.) tests. Unknowns involving two or three ions and group test a 1. Pour the solution into an evaporating dish and heat gently in hood to dryness. dark residue remains heati until ng solutions can be made by combining equal amounts of the above solutions without adversely affect only a pale solid the solid from step 1 in 2 1 M HaPO Then ng the results. When more ions are used the solutions should be made by pour the solution back into a tube. dd 1 mL of the 1 M Na HPO, to the test tube and divide it equally into three test tubes. combining the salts in 1 Lof 0.1 M HNOa (aq). 4 To the first tube add a spatula tip of Kland tir. Abrow Per Liter of Soluton 39 g of AINOsls9HO in 0.1 M HNOs (aq) olution. A red precipitate indicate nickel 6 g of Ba(Nobla in 0.1 M HNO (aq) 6 To the third test tube, add 1 mL of 1 and stir. A red-brown precipitate indicates eobal 60 g of 43 g of Co(NOhlr6Hao in water M HNOs aql, 6 MNHOH (aq) 38 g of CuINOa2.3HzO in water 73 g of F in 0.1 M HNoy (aq) Current address: Alabama School of Mathematics and Science 105 g of Mg(NOhla 6H2O in water King, G. B. Caldwel W. E.: Epstein, L semimicro Qualtatve Analysis: Wadsworth, 19e6 Mn? 54 g of Min(NOhla-6H2O in water Textook of Denney, R c.; Jeffery, G. H Mendham, J. Vogels tific inorganic Analysis, 4th ed. Longman scien 48 g of NINOhlz-6H20 in water Journal of Chemical Education

Explanation / Answer

Qualitative analysis of cations,

Net ionic eqauations,

Mg2+ : Mg2+ + 2HPO4- --> Mg(HPO4)2 (ppt)

Al3+

Al3+ + 3OH- --> Al(OH)3 (white ppt)

Al(OH)3 + OH- --> Al(OH)4^- (soluble)

Al(OH)4^- + H+ ---> Al(OH)3 (ppt)

Fe3+ + 3OH- --> Fe(OH)3 (ppt)

Fe(OH)3 + 3H+ --> Fe3+ + 3H2O

Fe3+ + SCN- --> FeSCN^2+ (dark red ppt)

Mn2+ + 2OH- --> Mn(OH)2

Mn(OH)2 + 2H+ --> Mn2+ + 2H2O

5Mn2+ + 5BiO3- + 14H+ --> 2MnO4-(purple solution) + 5Bi3+ + 7H2O

Ba2+

Ba2+ + CO3^2- --> BaCO3 (ppt)

BaCO3 + 2H+ ---> Ba2+ + 2H2O

Ba2+ + SO4^2- --> BaSO4 (ppt)

Ca2+

Ca2+ + CO3^2- --> CaCO3 (ppt)

CaCO3 + 2H+ ---> Ca2+ + 2H2O

Ca^2- + C2O4^2- --> CaC2O4 (ppt)

Cu2+

Cu2+ + 2I- --> CuI2 (ppt)

Ni2+

Ni2+ + 2DMG- --> Ni(DMG)2

Co2+

Co2+ + 1-nitroso-2-naphthol --> Co(1-nitroso-2-naphthoate) (ppt) + 2H+

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