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WALT’S PHARMACY

AND PHOTO STUDIO

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Santa Clara River

The River is Contaminated with metals

Possible contaminants are …

Ag+, Ni2+, Fe3+, Cr3+, Zn2+, and Ba2+

Ag+

Ni2+Cr+3

Zn2+

Fe+3

Ba2+

Who’s Guilty?

ObjectivesUltimately you are given a sample of the ions from the river water and you need to determine who is guilty and bring them to justice

First you will need to develop your own qualitative analysis scheme that can uniquely identify each ion in the mixture Ag+, Ni2+, Fe3+, Cr3+, Zn2+, and Ba2+

Creating your own Qualitative Analysis Scheme

You are going start by examining how each of the suspect ions reacts in a series of preliminary reactions

Reaction with dilute HClReaction with dilute NH3 and then conc NH3

Reaction with dilute NaOH and excess NaOHReaction with dilute H2SO4

You will then examine how each ion behaves in a pre-assigned confirmatory test

You will then use these results to create a flow diagram that helps to separate and uniquely identify the ions present in a mixture

Day 1: Preliminary TestsAg+, Ni2+, Fe3+, Cr3+, Zn2+, and Ba2+

To 10 drops of the solution add 20 drops 3M HCl Do you see any insoluble chlorides? What color are the solutions and the precipitates?

To 10 drops of the solution add 1M NH3 dropwise till basicDo you see any insoluble hydroxides (gels count)? What color are the solutions and the precipitates?add 10 drops of concentrated 15.0M NH3

To 10 drops of the solution add 1 drop 3M NaOH. (if not basic add 6M NaOH dropwise till basic)

Do you see any insoluble hydroxides (gels count)? Add 20 drops 3M NaOH and mix, do any ppts dissolve, color changes?add 10 3% H2O2 and heat of 5 mins in boiling water bath stir – note any changes

To 10 drops of the solution add 5 drops of 3M H2SO4

Do you see any insoluble sulfates?

Day 1: Confirmatory Tests

Ag+ testThe formation of white AgCl on addition of HCl is sufficient to confirm Ag+

Fe3+ testTo an Fe3+ solution (10 drops), add 5 drops of 0.2 M KSCN. This will form the complex ion Fe(SCN)6

3-,a deep red complex ion

Cr3+ testTo a CrO4

2- solution (10 drops), add 6.0 M HC2H3O2 until acidic; then add 2- 3 drops of 0.1 M Pb(C2H3O2)2 solution. A yellow precipitate of PbCrO4 will form

Ni2+ testTake 10 drops of Ni2+ solution; make it just basic with 6.0 M NH3. To this mixture, add 10 drops of dimethylglyoxime. The formation of red precipitate confirms Ni2+

Zn2+ testTo 10 drops of Zn2+ solution, add 6.0 M HNO3 until just acidic; then add 10 drops of K4Fe(CN)6. Formation of a pale yellow precipitate of K2ZnFe(CN)6 confirms Zn2+

Ba2+ testThe formation of white BaSO4 precipitate, on addition of 3.0 M H2SO4, is sufficient to confirm Ba2+.