Chemistry lab help, we will be testing for the presence of the following ions: C

Question

Chemistry lab help, we will be testing for the presence of the following ions: Ca2+,Co2+, Cu2+, Fe3+, Mg2+, Pb2+ , and Zn2+ .
- each of the following procedures can be described by a single chemical equation. write one balanced chemical equation each for test:

1) Ammonia Test for Complexation of Cu2+ To a test tube containing 6 drops of 0.10 M Cu(NO3)2, add 6 M NH3 dropwise until a deep blue solution is formed. The blue species is an amine complex of cupric ion, Cu(NH3)4 2+, that forms only under basic conditions. If no blue solution is formed, check the pH of the solution by placing a drop of the solution on a piece of litmus paper. If the solution is basic (pH > 8) but colorless, then no detectable Cu2+ is present.

2) Ammonium Oxalate Test for Ca2+ To a test tube containing approximately 6 drops of a 0.10 M Ca(NO3)2 solution, add about 10 drops of 0.10 M (NH4)2C2O4, ammonium oxalate. Formation of a precipitate indicates Ca2+ in the form of CaC2O4. (Strategy hint: If Co2+, Cu2+, Pb2+, Zn2+ are present, they will also form precipitates in the Ammonium Oxalate Test. ) 3) S & O Test for Mg2+ To a test tube containing approximately 6 drops of 0.10 M Mg(NO3)2 solution, add 5 drops of distilled water and 2 drops of 1 M HCl. Add 2 drops of S & O reagent and then 6 M NaOH dropwise until a Mg(OH)2 precipitate is formed. (Do not confuse a dark solution color with a precipitate.) (Strategy hint: If present, Ca2+ will also form a precipitate in the S & O Test.) 6

4) Thiocyanate Reaction for Co2+ To 5 drops of Co(NO3)2 , add 1 drop of 1 M HCl followed by a small amount of solid NH4SCN and 0.5 mL of acetone. A blue color confirms Co2+ in the form of Co(SCN)4 2- .

5) Thiocyanate Reaction for Fe3+ Dissolve several crystals of Fe(NO3)3 in a half-full test tube of distilled water. Transfer 6 drops of this solution to a second test tube and add several drops of 0.10 M KSCN solution. A red solution indicates Fe3+, mainly in the form of FeSCN2+ .

Hint: It is possible to write a balanced "partial reaction" equation showing only the species that must be present to create the color change or precipitate associated with that test. You are not required to include all of the reactant and product species. In chemistry terminology, such equations are known as net ionic equations

Explanation / Answer

1. Cu(NO3)2. 3H2O + 4NH4OH ----> [Cu(NH3)4](NO3)2 + 7 H2O

2.Ca(NO3)2 + Na2C2O4 = CaC2O4 + 2 NaNO3

3. Mg(NO3) 2 + 2NaOH = Mg(OH)2 + 2NaNO3

4. Co(NO3)2 + 4NH4SCN = (NH4)2[Co(SCN)4] + 2NH4NO3

5. Fe^3+ + SCN^- ----------> Fe(SCN)^2+   (this is net ionic reaction)

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