1. Lab Session 9
This is a two-week experiment in which they will explore how to use chemical reactions to identify substances.
How can we use chemical reactions to identify substances? (Two-Week Experiment)

2. What different metals are present in the ore?
Your 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.
Present the challenge to be faced in this two-week experiment.
What different metals are present in the ore?

3. 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.
Link to the lecture in terms of now using chemical reactions to identify what substances are in a system.
We can use some of these chemical reactions as differentiating characteristics to identify the ions.
Weak electrolyte

4. Qualitative Tests
In 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 6H2O Cu(NO3)2 3H2O Fe(NO3)3 9H2O Ni(NO3)2 6H2O Ba(NO3)2

5. You will have 30 minutes Calculations Preparation
Skill Building Tests
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.
You will have 30 minutes Calculations Preparation
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
Stress that they will need the solution for this week and the next. The plastic bottle in their locker is for storing this solution. Make them show you their procedure before beginning. Make sure the calculated amount of salt is correct. ASK EACH GROUP TO PREPARE TWO OF THE SOLUTIONS>

6. Other Solutions
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 Phosphate Na2CO3 – Sodium Carbonate
Here’s the list of anion solutions M solutions of these are provided by the preproom.
Emphasize the importance of recognizing the names and formulas of these six anions. We will not be using the chloride.

7. Your First Challenge
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.
Available resources:
Cation and anion solutions;
A well plate
Volumetric glassware.
Show them the well plate and discuss its use. Send them into the lab to complete the challenge. Instruct them to return and post their results to the board. Emphasize the importance of make systematic observations and record their results.
You have 45 minutes

8. Share Results and Reflect
Present your results to the class. Decide as a group which data should be shared to facilitate the analysis.
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.
Discuss the results with the class. Students should develop a clear sense of how they can use the different precipitation reactions that they observed to identify the cations or anions involved.

9. - = no PPT 1 = small amount, 2 = med, 3 = lots
initial color
CO32-
C2O42--
OH-
PO43-
SO42-
Ba2+
clear
+2 white
+1 white
+2 white
+3 white
Al3+ -
Co2+
pink
+2 pink
+1 pink
+2 teal
+3 purple
Cu2+
blue
+2 blue
+1 blue
+2 blue
Fe3+
yellow
+2 orange
+1 orange
+3 yellow
Ni2+
green
+3 white
Example of expected results.
- = no PPT = small amount, 2 = med, 3 = lots

10. 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.
Solubility data is not enough to create an analysis scheme. We’ll give them a few more reactions to evaluate. They should think of the reactions as tools in their qualitative analysis tool box.

11. This Week’s Challenge
Perform at least four of the following reaction tests on each of the cations. Create a table of your observations.
Alizarin S Reaction Aluminon Reaction Cinchonine Reaction Dimethylglyoxime Reaction Nitrosonaphthol Reaction Hydrogen Gas Reaction
Available resources:
Cation solutions;
Test solutions;
Well plates;
Glassware.
This requires active management on your part. Each student in a group should complete one of the tests. Different groups should complete different tests in such a way that, when reporting results, there is data for all of the tests by at least two different groups.
You have 60 minutes

12. Share Results and Reflect 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.
Create a chart on the board for them to fill in. Once you have sufficient data, bring them all together to discuss.

13. (all evolved gas & heat upon Zn addition)
Alizarin
Aluminon
(NH4OH added to pH ≈ 8)
Cinch.
DMG
Nitroso
(reagent is yellow)
H2 Gas
(all evolved gas & heat upon Zn addition)
Ba2+
AL→2 PPT
acetic(5)→clear soln, red PPT
acetic→N/R
NH4OH→light peach soln
N/R
HCl→N/R
Al3+
AL→3 no PPT
acetic(4)→brightorange solution
NH4OH→+2 rose
Co2+
AL→orange PPT
acetic(5)→yellow soln, purple PPT which disappears over 5min
NH4OH→light pink soln
orange soln
+1 green
+3 red
HCl→bright blue soln
Cu2+
acetic(25)→ orange soln
NH4OH→light purple soln
+3 dark brown
+1 dark orange
HCl→yellow soln
Fe3+
AL→1 PPT
acetic(10)→clear soln, brown PPT
acetic→orange soln
NH4OH→clear soln, +2 brick red
+2 brick red
+3 black
Zn→black metal particles on liquid surface
Ni2+
AL→5 PPT
acetic(10)→ orange soln
+3 bright pink
Example of expected results.
N/R = no reaction (no visible change) soln = solution = PPT 1 = small amt, 2 = med, 3 = lots Alizarin Notation AL = Alizarin S reagent, purple color rating 1→5 (1=brick red, 3=purple, 5=royal blue), PPT=precipitate, acetic(n) = n drops acetic to remove violet color

14. 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.
NOW they should have enough information to be able to create an analysis scheme. This they will do as groups under your direction. Whatever they don’t finish in class will have to be done as homework.
Introduction of the concept of a flow chart. This is perhaps the most famous example. Although meant to be humorous, it does a nice job of illustrating how a flow chart works. A question is asked and the answer determines what the next question will be. A series of such questions leads the user through a maze of all possible outcomes.
Your scheme should be constructed as a flow chart.

15. Another Example
Here’s an example involving chemical reactions. This is roughly the complexity they should expect for their flow chart. They should all begin by creating a box at the top of the page that includes all ions they are considering.

16. Hints
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).
Ba2+ , Al3+ , Ni2+, Cu2+
C2O42-
Ni2+ , Al3+
Solution
Precipitate
Ba2+, Cu2+
Separate?
Separate?
Re-dissolve HNO3

17. 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.
Ask students to present part of their schemes. You need to help them in the development of the scheme; they are going to be lost and confused. See next slide as an example of a good flow chart for this experiment.

18. Co2+, Ba2+, Cu2+ Al3+, Fe3+, Ni2+ solution Al 3+, Cu2+ SO42-
excess 6M HCl
(4x volume of Ba 2+ Ca 2+ Co 2+ Cu 2+ Fe +3 Ni 2+
original solution)
blue or green solution
confirms Co 2+
PPT
Solution
Co2+, Ba2+, Cu2+
C2O42-
Al3+, Fe3+, Ni2+
PPT
solution
PPT
solution
Al 3+, Cu2+
SO42-
Fe3+, Ni2+ v Ba 2+
OH-
Al3+
redissolve
HNO 3
Example of expected flow chart based on the experiments done in this lab. There are many other possibilities.
solution
PPT H2
Gas
Cinchonine
Or Cinchonine
DMG
Cu2+
PO43-
solution
metallic
pink PPT
particles
PPT
Co2+
OH-
Co2+ v
Fe3+
Ni2+
Al3+

19. Week Two Pre-lab Assignment
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.
No report. If their scheme is already designed there is also no additional pre-lab assignment.