Submitted by Marites (Tess) Guinoo / University of St. Thomas on Wed, 08/04/2010 - 17:16
##### Categories
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Description

Most of my first year students have a hard time understanding what a limiting reagent is.  I found this website through the Computational Chemistry for Chemistry Educators workshop I attended during summer 2011. This is one of the many interactive simulations from University of Colorado-Boulder.

Learning Goals

A student should be able

• to explain what a limiting reagent is
• identify what is the limiting reactant in a chemical reaction
Implementation Notes

Here is my typical script:

Me: I open the simulation in the sandwich shop tab, then say:

Our topic is Limiting Reagents, but before we talk about this, I want to make a cheese sandwich.  If I am making one cheese sandwich, how many pieces of bread do I need?

Class: 2  (I then place 2 next to the bread)

Me: How many cheese strips do I need?

Class: 1  (This number will vary, but for the sake of simplicity I normally guide them to tell me 1 here.  I place 1 next to the cheese)

Me: (They now see that I produce 1 cheese sandwich.) So, I need 2 bread and 1 cheese to make 1 cheese sandwich.

Me: If I have 6 pcs of bread and 2 pcs of cheese, how many cheese sandwiches do I have?

Class: 2 (Usually in chorus)

Me: Are you sure?  See I am not strong with my math skills.  I will need help with a simulation. (I will put 6 next to the bread and 2 next to the cheese)

You are right.  I have 2 cheese sandwiches.

What else do I have?

Me: Why?

Class: Because you do not have enough cheese. (At this point, some of the students are seeing where I am going)

Me: So, the cheese limits the sandwich making.  In chemistry language, it is the limiting reagent.

Me: Now if I have 6 pcs of bread instead, and keep 10 pcs of cheese.  How many sandwiches do I have?

Class: 3

Me: What else do I have?

Class: 7 pcs of cheese

Me: So which one is the limiting reagent?  Cheese or bread?

Me: I now switch to the real reaction tab, and use the make water button.

If I synthesize water, I need 2 moles of H2 and 1 mole of O2 to make 1 mole of water.

If I have 6 moles of H2 and 2 moles of O2, how many moles of water do I make?

Class: 4

Me: What is the limiting reagent?

Class: O2

Me: What if I have 6 moles of H2 and 10 moles of O2, how many moles of water do I make?

Class: 6

Me: What is my limiting reagent?

Class: H2

After this, I will tell them that the link to the website is posted and they can go back to it as much as they can.  I then proceed to do a sample problem from the end chapter of the book on the board.

##### Evaluation
Evaluation Methods

I do not have an evaluation method for this, but this concept will eventually be in a quiz or exam.

Evaluation Results

Most of my students like this web resource.  They like that they can go the simulation on their own to play around.