Problem-Based Labs


Many of the traditional labs we perform as instructors can be altered slightly to make them more of a problem based lab. Two instructors (David A. Tarcy and  Ellen Loehman) have made contributions in this area  Below are their suggestions.  If you have any send them in and I will add them to the list.  

1) Determine the rate equation for a 1st or 2nd order rxn and set the conditions to make the reaction happen in x sec.

2) Plan and perform an electrolysis of lead II bromide to obtain 2.500 g of lead. ( A favorite of mine as the molten lead soldifies in the bottom of the crucible, not on the cathode, and results are within 1 %)

3) Make a solution of "rust remover" by use of a redox table and evaluate its effectiveness.

4)Determine if the reaction between iron (steel wool) and copper sulfate solution produces iron II or iron III sulfate and copper. (Good lab for introductory stoich. students)

In my mind when I set "problem labs" I want to see evidence of planning and evaluating their chosen methods of approach. The problem should be a clearly defined goal: "Obtain 2.500 g of Pb", but it is the what they are doing and why they are doing it thinking which clearly takes time and is well worth it. I have seen many introductory students perform experiments without a clue of why they are using the apparatus given to them or understanding of many of the steps. Planning, or problem labs, is a definate help in overcoming this weakness.


Questions? Comments??
David A. Tarcy
Jakarta International School
Jakarta, Indonesia


1. Separation of a mixture
In the past, I gave students a mixture of CuSO4, sand and iron filings with a set procedure. The goal was to separate and find the % by mass of each component. This year I gave them various mixtures without a procedure with the same goals. They needed to use a CRC or Merck Index to look up properties and propose a method of separation. It took about a day longer, but it was worth it.

2. Energy in a peanut
I have used this lab that makes a calorimeter from a coke can, with a peanut as fuel. The goal is to calculate the kcal/g and compare it with the accepted value. This year, I gave them the same procedure, but asked them to modify it the second time to reduce the error. This was VERY instructive in exposing student misconceptions about heat content and transfer.

Questions?  Comments??
Ellen Loehman
Manzano High School
12200 Lomas Blvd NE
Albuquerque, NM 87112

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