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Lab Session 9

How can we use chemical reactions to identify substances?

(Two-Week Experiment)

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IYour Challenge

Imagine that you work for a mining company that is about to buy a new mine in Southern Arizona.

You have been asked to identify the metals present in samples of the ore extracted from the mine.

What different metals are present in the ore?

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Weak electrolyte

Solubility

Many ionic compounds dissolve in water, or can be dissolved

using acids, and the ions separate in solution.

When combined with other substances, the ions may recombine to form new products

(chemical reaction) with characteristic properties.

We can use some of these chemical reactions as differentiating characteristics to

identify the ions.

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Qualitative TestsIn order to identify the metal ions in a mineral, we need to first explore how known metal ions

react with different substances.

This week you will explore how known metal ions react with a variety of substances.

Your first task is to prepare the solutions of the known metal ions to be tested.

Al(NO3)3 9H2O Co(NO3)2 6H2OCu(NO3)2 3H2O Fe(NO3)3 9H2ONi(NO3)2 6H2O Ba(NO3)2

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Available resources: Balances; Volumetric glassware;

Ionic salts: Al(NO3)3 9H2O, Co(NO3)2 6H2O, Cu(NO3)2 3H2O, Fe(NO3)3 9H2O, Ni(NO3)2 6H2O Ba(NO3)2

You will have 30 minutesCalculationsPreparation

Your groups needs to prepare 100 mL of one 0.1 M of the metallic cations.

Save this solution in a labeled bottle (you will need it next week).

Discuss how the work will be divided among all of the different groups.

Skill Building Tests

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Now that we have solutions of the cations we can proceed to react them with solutions of

anions. You will use the following anion solutions

provided by the prep-room.

Na2SO4 – Sodium Sulfate Na2C2O4 – Sodium Oxalate NaOH – Sodium Hydroxide K3PO4 – Potassium PhosphateNa2CO3 – Sodium Carbonate

Other Solutions

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Combine all of the cations (6) with all of the anions (5) to determine if there is a

characteristic chemical reaction that can be used to identify them.

You have 45 minutes

Available resources:

Cation and anion solutions;

A well plate

Volumetric glassware.

Your First Challenge

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Present your results to the class. Decide as a group which data should be

shared to facilitate the analysis.

Share Results and Reflect

In your groups, discuss how you may identify any given ion. As a class discuss whether these set of reactions are enough to separate/identify all of the cations.

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Additional Tests

The reactions that you have observed may not be enough to build a full

SEPARATION/IDENTIFICATION scheme for all of metallic cations present in a

mineral. To enrich our set of analytical tools, let’s explore some other reactions.

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Perform at least four of the following reaction tests on each of the cations.

Create a table of your observations.

You have 60 minutes

Available resources:

Cation solutions;

Test solutions;

Well plates;

Glassware.

This Week’s Challenge

Alizarin S ReactionAluminon Reaction

Cinchonine ReactionDimethylglyoxime ReactionNitrosonaphthol ReactionHydrogen Gas Reaction

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Add your results to the chart on the board.

As a class, discuss whether you have

enough data to build an

identification scheme for all of

the cations.

Share Results and Reflect

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Qualitative Analysis Scheme

You should now have sufficient tools to create an analysis scheme.

Your scheme should be able to tell you

which of the cations are in a sample

regardless of what ever else is there.

Your scheme should be constructed as a

flow chart.

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Another Example

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Ba2+ , Al3+ , Ni2+, Cu2+

C2O42-Ni2+ , Al3+

Solution Precipitate

Ba2+, Cu2+

You can add an anion to precipitate some cations in a mixture, and leave others in solution;

You can separate the solid mixture by filtration or decantation and then re-dissolve it using an acid, such as nitric acid (HNO3).

Separate? Separate?

Re-dissolve HNO3

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Claims and Evidence

Based on the results of your experiments, present your proposed

analysis scheme and the evidence that you have to support your ideas.

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No Report of this Week

Week Two Pre-lab Assignment

You are to design and construct an appropriate analysis scheme for determining the presence of the selected cations in an ore sample.