My Students are Joining the Army Corps of Engineers

Inquiry in Chemistry

...Is pretty difficult to pull off.  Here is why:

Inquiry education refers to letting students ask and answer their own questions, and arming them with the tools and some of the background knowledge to generate their own knowledge.  It's about putting them in charge- making them responsible- for their own learning.

An uncritical chemistry instructor bent on doing inquiry labs with inexperienced sophomores is likely to set his lab ablaze with a chemical fire or suffocate the southwest wing of the building with hydrogen sulfide.  You will find that many early chemists perished by means of their own experiments (one notable exception being Antoine Lavoisier, who was beheaded at the climax of the French Revolution after being [falsely] convicted selling adulterated tobacco and giving money to France's enemies).  But it was precisely this debonair chemical playfulness and curiosity that landed some of the greatest foundational discoveries of the chemical sciences.  How can a chemistry teacher encourage this curiosity without also encouraging a building evacuation?

Here I am going to put forward an example of how I am encouraging inquiry in chemistry, and propose a model for how it can be implemented in a wide array of science lessons.

Reactions and Stoichiometry

Being able to categorize reactions by their type is crucial for students of chemistry, because it helps them develop a framework for the behavior of compounds and elements when they combine, break apart, or rearrange.  In inorganic chemistry there are 5 recognized reaction types:

Synthesis- 2 or more elements combine to make a new compound.  A + B --> AB

Decomposition- A compound is broken down into smaller pieces.  EF --> E + F

Combustion- A compound is combined with oxygen to produce 2 or more oxides.  JK + O2 --> JO + KO

Single-replacement- An element reacts with a compound to replace one ion.  A + BC --> B + AC

Double-replacement- Two compounds react and exchange ions, resulting in a gas, precipitate, or water.  AB + CD --> CB + AD

The SUPER important thing to recognize with the last two bolded reactions is that they can be used to selectively remove an ion from a solution.  For instance, if my solution is contaminated with aqueous (dissolved) silver nitrate, I can add a little sodium chloride and form what is a called a precipitate, or the visible, white, insoluble compound silver chloride:

AgNO3(aqueous) + NaCl(aqueous) --> NaNO3(aqueous) + AgCl(solid)

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Now we can just filter out the white AgCl crystals, and the silver is gone forever!  

Or suppose the water is contaminated with iron(III) chloride, the same nasty stuff at the center of an earlier blog post.  I can perhaps selectively precipitate out the iron(III) ion if I can replace it with a metal that is higher in what is called the "activity series" of metals.  A metal higher on the activity series will kick out a lower metal, resulting in a precipitate, through a single-replacement reaction.  I might try the reaction below.

FeCl3(aqueous) + Ca(solid) --> CaCl2(aqueous) + Fe(solid)

As long as I add just enough calcium metal to the dissolved iron(III) chloride, I convert that acidic, carcinogenic substance into harmless calcium chloride salt, a common food preservative.  I would be able to tell whether this reaction worked because iron(III) chloride is a dirty ochre color; if it is removed from the solution and replaced with calcium chloride, then the solution should go from dark yellow to clear (or at least less yellow).

You need to have some background in chemical reactions- and a sense of creativity- to make the predictions I made above.

The aim is for my own students to see this on their own and realize that they can do the same thing with a little research and creativity.  For them to do this, they will have to have a clear sense of how replacement reactions work, understand the solubility rules (only certain compounds are soluble in water), and also predict if a reaction will happen based on the activity series of metals.

"Stoyk- Stoykee- wait, what?"

These are the words of one of my male students upon first hearing the term "stoichiometry" [stoyk-ee-om-etree].  This science combines a knowledge of molar mass and reactions to allow the chemically curious to predict the outcomes of reactions as far as reactant mass, yield, and percent yield.  In other words, stoichiometry allows you to know exactly how much of your ingredient substance(s) you should measure in order to get the desired amount (usually mass) of product(s).  We use a unit called the "mole," which represents 6.02x10^23 particles, to describe quantitative relationships in chemistry.  If we know how much a mole of a certain element or compound weighs, we can use this conversion to correctly assign masses to our substances in the reaction.

Now this is all a little abstract or abstruse to most, but understanding stoichiometry is absolutely essential to describing the mass-relationships of chemical reactions and how do do actual lab work.  There is literally no other way to do it.  And it is very math-intensive.

So how do we turn a stoichiometry lesson into an inquiry unit?  What follows is how I am going to try.

How My Students are Joining the Corps

I have come to find that one of the pillars of inquiry education is concrete goal-setting and, to a small extent, role-playing.  The goal is a freshwater lake cleanup, and the role is a chemist in the Army Corps of Engineers.

In class we will suppose that there has been a major spill of a toxic salt in Lake Saint Clair, indicated by the white X at left.  In 2003 there was a toxic vinyl chloride spill in Lake Saint Clair, and people had to stay out of the water and not eat any Saint Clair fish for a while.  We'll use that as a hook.

Each pair of students will act as a team to rid the water of the contaminant, using their knowledge of reactions and stoichiometry.  I will assign different chemicals to different groups, partly by difficulty (some salts are easier than others to clean up).  Below are the amounts and types of salts that students will be responsible for removing from Lake Saint Clair.

14,200 kg of copper(II) sulfate: CuSO4

19,900 kg of potassium chromate: K2CrO4

26,300 kg of barium chloride: BaCl2

11,150 kg of sodium hypochlorite: NaClO

27,500 kg of lead(II) nitrate: Pb(NO3)2 (maybe)

The bold ions are the toxic ones, so these are the particles that students are trying to remove from the water supply.  Free copper, barium, and lead ions are all pretty toxic, and chromate and hypochlorite are pretty nasty too.

Not only will students need to perform reactions that will remove the offending ions from a solution, they will then have to do stoichiometric calculations to predict the mass of reactant(s) they will need to perform this procedure.

The key to solving the problem lies in research, understanding reactions, and devising creative lab solutions.

What My Corps Engineers Will Do

The teams will first have to do some background research and make a general proposal of how to remove the toxic compound from the water.  Following are the steps they must take in this process.

1. Research the chemical's properties: taste/smell, color, density, solubility, toxicity, reactivity, etc.
2. Identify at least 2 reactions that can remove the offending ion from the water.  Any solution will (probably) require a single-replacement or double-replacement reaction.
3. Calculate how much reactant will be required to remove 2.0 g of the offending compound from a solution.
4. Identify how they will know whether they have removed the offending ion. 
5. Compile the above information into a formal lab proposal.

Next they will need to do some work in the lab.  After I have gone over their lab proposals and OK'd one of the reactions they think will work, they will perform that reaction to see if it is effective in removing the substance.  The steps they will need to take are as follows.

1. Dissolve 2.0 g of the toxic substance in a small amount (maybe 100 ml) of water.
2. Perform the reaction using the mass of reactant that they calculated in the formal lab proposal above.
3. Evaluate the effectiveness of their reaction.
4. Record all materials and methods of their lab procedure.
5. Propose how to scale up the successful reaction so that it can be used to remove the given mass of toxic substance.  Show calculations.
6. Compile the above information into a formal lab report.

What this Unit Will Look Like

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Let me put a human touch on the whole proposition so it is clear what I intend for this unit to look and feel like to me- and more importantly- to my students.

Students will immediately feel uncomfortable, because I will not be giving them a single set of instructions on how they are to perform their lab procedure.  Upon assigning the work, they will not be very strong with the whole idea of stoichiometry, but this will improve over the course of the unit.

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Students will have to collaborate closely in order to uncover how to remove their respective offending ions from the solution, and this is where I will have to put in a lot of effort in guiding them toward lab work that will be productive.  The purpose of the first research assignment is simply to let them explore their compound on their own, make predictions about reactions, then get my approval on how to proceed (I want them to succeed, so I will have some say on how they may wish to go about working in the lab).

The scary part will be when they get into the lab and start employing the methods they have devised.  They will have to be able to predict stoichiometric relationships so they do not waste chemicals or perform an inefficient reaction.  They will have to weigh and record their reactants and infer whether the reaction has worked, as I did in my examples above.  

They will have to work to express professionally what they are considering and what they have done to solve the problem.  They need to communicate their progress to a boss in writing.  

This is high-level depth of knowledge that I hope to see them achieve on their own.  It is the dream of every imaginative educator.

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The Proposed Model

I said I would propose a general model of what I do to support inquiry learning, and it is outlined below.

1. Students are presented with a clearly-defined problem that implies a clearly-defined goal.
2. Students are allowed the ability to research their problem independently, then refer to instructor for guidance and advice.  If working with others, this is a good opportunity for group collaboration.
3. Students attempt their solution in an "as-close-to-reality" setting as possible.
4. Students evaluate the efficacy of their solution.
5. Students may also make recommendations on how to enhance their solution: How to scale it up, How to improve its efficiency, How to apply it to other scenarios.