S'mores Mole Ratios Lab
Materials
Electronic Balance, Paper Plates, Chocolate chips, Graham crackers, Marshmallows
Purpose
This activity is designed to allow students to understand the concept of limiting reagents in reactions.
Background
Imagine you are going on a camping trip with some of your friends. You are going to go hiking in the woods, swim in the lake and sing songs around the campfire. But that is not all the campfire is for. You and your friends planned ahead and brought supplies to make s’mores. One of your friends brought marshmallows, another brought graham crackers and yet another brought chocolate bars. Unfortunately, none of you planned out how much of each ingredient you would need to make the number of s’mores you wanted. So exactly how many s’mores can you make given the amount of ingredients you have? In this activity you answer that question and figure out which ingredient you need more of most, which will be termed the limiting reagent.
For this activity, each of the ingredients will represent a different element
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Marshmallow (M)
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Graham Cracker (G)
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Chocolate bar (Cb).
Since the Graham cracker is always used in pairs, it is a diatomic element and will be represented as G
2
in this activity.
Procedure:
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Decide how you are going to make your s’more and how much of each ingredient you will use. You can shirk conventions here—customize the s’more recipe and make it your own.
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Write down the empirical formula for your s’more using the element key above. Make sure you take into account what the chemical name of your product is.
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Write and balance the number of ingredients of each side of the equation for your s’more.
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Form as many s’mores as you can. How many s’mores were made?
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What was the first ingredient that you ran out of in this experiment? This was the limiting reagent. What ingredients did you have left over? These were excess reagents.
Stoichiometry lab
Purpose
To determine, through experimentation, the stoichiometric ratio of reactants that generate a gas.
Materials
Acetic Acid, Sodium Bicarbonate, Balloons, Erlenmeyer Flasks, Graduated Cylinder, String, Metric Ruler
Procedure
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Weigh out the following quantities of sodium bicarbonate, or baking soda. Use a funnel to add the baking soda to each balloon. Be sure to insert the funnel securely into the balloon so that the baking soda is deposited at the bottom of the balloon.
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Balloon #1 - 0.18g
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Balloon #2 - 0.35g
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Balloon #3 - 0.52g
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Balloon #4 - 0.70g
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Balloon #5 - 1.00g
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Balloon #6 – 3.00 g
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Measure 10 mL of acetic acid in a graduated cylinder
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Add 10mL of acetic acid to the beaker.
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Attach a balloon containing the sodium bicarbonate to each beaker, being careful not to let the sodium bicarbonate mix with the acetic acid.
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After the balloon is securely attached to the beaker, carefully and slowly lift the balloons to allow the sodium bicarbonate to mix with the acetic acid in the beaker. Repeat with all balloons.
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Observe, paying special attention to the size of the balloons after the reactions. You can measure the diameter of each balloon. Hold a ruler horizontally and measure the largest diameter across each balloon, being careful not to change the shape of the balloon.
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Record your observations for each trial in the table below.
Balloon #
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1
|
2
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3
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4
|
5
|
6
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Amount of sodium bicarbonate (g)
|
0.18 g
|
0.35 g
|
0.52 g
|
0.7 g
|
1.0 g
|
3.0 g
|
Diameter of balloon (mm)
|
|
|
|
|
|
|
Calculations to determine volume:
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Determine radius first by solving for ‘r’: 2r=diameter
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Use ‘r’ to solve for volume of balloon: Volume=4/3πr
3
Observations
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Does each balloon inflate to some degree? Why?
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Make a graph of the diameters vs. balloon number. Make balloon number the independent variable.
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Use your observations and the graph to compare the degree to which each balloon inflated.
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