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Definitions: Stoichio means element and metry means the process of measuring. The mass and quantity relationships among reactants and products in a reaction are found using the process of stoichiometry.
Problem:
If you are given one bag of large marshmallows, what is the maximum number of Smores that can be made?
How many boxes of graham crackers and how many chocolate bars are needed to make this many Smores?
Solutions:
1st Step: Write a chemical equation using the following symbols:
SubstanceSymbolUnit Mass Graham CrackerS7.00 gMarshmallowMm7.10 gChocolate PiecesOr3.30 gSmoreS2MmOr3________ g
Calculate the unit mass of the Smore (S2MmOr3)below:
2nd Step: Balance the equation: What does the equation tell us? What do the coefficients represent?
They represent the ratio of the ___________ or the ______________.
3rd Step: Calculating the number of units (or moles) given:
Determine the number of unit marshmallows that are available in the bag. If there are 454 g marshmallows in one bag, how many marshmallows do you have?
4th Step: Finding the units of other substances in the reaction:
Now, determine how many units of graham crackers and chocolate segments are needed to make the maximum number of smores available.
5th Step: Convert your number of graham crackers and chocolate segments into mass (gram) values:
When you go to the store, you cannot quickly determine the exact number of graham crackers or chocolate segments there are in a box or bar. The mass is easy to read, however. Using mass values, you can quickly determine how much you need to buy.
6th Step: Finally-convert the masses into your needed units.
In this case, if a box of graham crackers has a mass of 254 g, how many boxes do you need? Also, if one chocolate bar has a mass of 49.5 g, how many bars do I need?
Now we will transfer this process into the language of chemical reactions. When you complete this problem, get it checked by your teacher and you will be rewarded with the necessary items to make your Smore!
If we were to add a piece of solid Cu to an aqueous solution of silver nitrate, the Silver would be replaced in a single replacement reaction forming aqueous copper (II) nitrate and solid silver. How much silver is produced is 15.00 grams of Cu is added to the solution of excess silver nitrate? Show all work and dont forget to use significant figures.
Steps 1 and 2: Write and balance the chemical equation:
Step 3: Convert g Cu to moles Cu:
Step 4: Convert moles of Cu to moles of Ag produced:
Step 5: Convert moles Ag to grams of Ag produced:
Step 6: If silver metal sells for %4.50/ounce, could you get rich from this lab? (How much would it be worth?) Conversion factor: (1 gram = 0.0353 oz)
Extra: Try writing this entire stoichiometric process on one line. Remember to cancel out all necessary units!
Introduction to Stoichiometry
HASTI 2003
Objectives:
This lesson will serve as an introduction to reaction stoichiometry. The student will be able to predict the quantities of substances needed or produced in a chemical reaction by using stoichiometric relationships.
Prior Skills to Review:
Writing chemical formulas
Writing and balancing chemical equations
Mole/Mass conversions
Molar Mass determination
Molar ratios in a chemical reaction
Lesson Extensions
Calculate quantity of a substance produced or needed in a reaction given a balanced equation and a certain quantity of another substance in a reaction.
Perform a chemical reaction in lab between a known amount of sodium bicarbonate and excess acetic acid. Determine theoretical yield, actual yield, and percent yield of the sodium chloride produced. Report data and calculations on a lab report and be able to make the same calculations on a new data set.
Connections:
The Nature of Chemical Change
C.1.9 Describe chemical reactions with balanced chemical equations.
C.1.12 Demonstrate the principle of conservation of mass through laboratory investigations.
C.1.12 Use the principle of conservation of mass to make calculations related to chemical reactions. Calculate the masses of reactants and products in a chemical reaction from the mass of one of the reactants or products and the relevant atomic masses.
The most fun part of this lesson is when the students get to turn in their problem and then receive the material to make their own smores. You may wish to let them make the smore then place it in the microwave for 15-20 seconds. Be careful of it tipping over. This is a really boring way to do it, however, compared to letting them roast their marshmallows over a Bunsen burner. This is an activity your students will talk about when they see you years down the road. Why not let one of their fondest chemistry memories be about Smore Stoichiometry?
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Smore Stoichiometry Title
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