Chemistry Lab Handout 15   "Stoichiometry with Legos"

Your Name:    ___________________________________ Role:______________

Lab Partners: ________________Role:_____   ________________Role:_____

Problem:  How can you determine how many atoms or molecules or formula
          units are necessary for a chemical reaction to take place?

Hypothesis:   _______________________________________________________

     _________________________________________________________________

     _________________________________________________________________

Materials:                        assorted Legos

Caution: (no special concerns)

Procedure:
This Activity will use Legos to begin to help you to understand the relationship between the number of atoms and molecules/formula units in a reaction, as well as the ratios in which these molecules and atoms react. 

First of all, you will need to assign an atom to a Lego that has a certain size and color. The type of Lego you choose will represent that atom for the rest of the activity. For example, if you choose a red 2x4 Lego to represent oxygen, then it will represent oxygen for the entire activity. A different Lego (shape and/or color) must represent each atom.

These are the Atoms that you will use:

Type of Atom	Lego (your choice)	Type of Atom	Lego (your choice)
Copper (Cu)   2x		Aluminum (Al) 2x
Oxygen (O)    8x		Cobalt (Co)   6x
Hydrogen (H)  4x		Phosphorus (P)2x
Chlorine (Cl) 6x		Potassium (K) 6x
Bromine (Br)  4x		Sulfur (S)    3x

Okay, now that you have chosen Legos to represent your atoms, it is time to make models of certain reaction.

Draw reactions as if the Legos were the actual atoms.
Example:

          For the reaction  2H₂   + O₂  à  2H₂O 

The Legos may look like this:

H     H

                                     

H     H

H     H

H     H

O            O

           +         à            

O

O

    

After each reaction, there will be a few questions that you should answer before you proceed to another reaction.                   

Lets Get Started! (Everywhere you see a pencil box , you must draw.)

1. CuO  +  H₂ à  Cu   +   H₂O  

Draw the Lego models of this reaction.

Questions for Reaction #1.

(a) How many formula units of CuO did you make for the complete

reaction? ________

(b) If you used 2 CuO’s, then how many H₂’s would you need for the

reaction to be balanced? ________ 

Using Legos, make a model of 2 CuO’s reacting with 2 H₂’s. Draw the model below.

(c) How many Cu’s can you make from the reaction in question (b)?

________

(d) How many H₂0’s can you make? (use your drawing from b) ________

2. Cl₂   +   2KBr  à  2KCl   +   Br₂

Build the Lego Models and then draw models of this reaction.

Questions for Reaction #2.

(a) How many KBr’s did you make for the complete reaction?  ________

(b) How many Br₂’s did you build? ________

(c) If you used 4 KBr’s, then how many Br₂’s would you get? ________

Make a model of 4 KBr’s reacting with 2 Cl₂ ‘s. Draw the model below.

3. When you add aluminum to sulfur, you are basically combining 2 aluminums and 3 sulfurs.  Therefore, the reactant side of the reaction looks like this:

2Al   +   3S

Questions for Reaction #3

(a) Make the reactants with your Legos and draw the models below.

(b) Build the product of this reaction with your Legos and draw it below.

(c) How many sulfur’s do you need for every 4 Al’s? ________

Show this with a drawing.

This relationship between the sulfurs and the aluminums is called the MOLAR RATIO!
4. The reaction of potassium sulfate and cobalt(II) chloride is a double displacement reaction. It looks like this:

             K₂SO₄   +   CoCl₂  à  2KCl   +   CoSO₄

Make a model of this reaction with the Legos and find the mass of each reactant and each product.

Draw the model of each individual compound below.

Molecule	Molar Mass (g)
K2SO4
CoCl2
KCl
CoSO4

Questions for Reaction #4

(a) If you have 2 K₂SO₄ but only 1 CoCl₂ how many KCl’s could you make? ________

(b) Which is the limiting reactant? ______________________

Make the model of your answer and draw it below.

(c) If you wanted 2 CoSO₄ ‘s, how many CoCl₂‘s would you need? ________

(d) How many grams of CoCl ₂ would you need to make 2.00 moles of KCl?
Show your work:

 

 

(e) How many grams of KCl would you get if you started with 6.00 moles
of CoCl₂?
Show your work:

 

 

(f) If you wanted to produce 15.00 moles of CoSO₄, how many grams
of K₂SO₄ would you have to start with?
Show your work:

 

 

 

Conclusion: _________________________________________________________

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