STOICHIOMETRY
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Transcript of STOICHIOMETRY
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STOICHIOMETRY
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• I CAN solve a stoichiometry (mass – mass) problem using a chemical equation and mass data.
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What is Stoichiometry?
• Stoichiometry is the quantitative study of reactants and products in a chemical reaction.
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What You Should Expect To Do?
• Given : Amount of reactant(s)
• Question: How much product(s) can be formed?
• Example • X A + Y B ? C
• “Given X grams of A and Y grams of B, how many grams of C can be produced?”
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What Skills Do You Need?
Some skills you will need to use:
• Molar Ratios (come from coefficients of a BALANCED equation).• Molar Masses (Formula Weight calculations).
• Balancing Equations
• Conversions between grams and moles
Note: This type of problem is often called "mass-mass."
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Steps Involved in Solving Mass-Mass Stoichiometry Problems
• Balance the chemical equation correctly.
• Convert GRAMS to MOLES of the starting substance.
• Set up a MOLE RATIO between starting and ending substances.
• Convert MOLES to GRAMS of ending substance.
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Mole Ratios
A mole ratio COMPARES moles of one compound in a balanced chemical equation to moles of another compound (look at their coefficients).
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ExampleIn the reaction between magnesium and oxygen to form magnesium oxide, what
is the mole ratio for the substances?
2 Mg + O2 2 MgO
2 moles : 1 mole : 2 moles
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Steps to Solve a Stoichiometry Problem
• Make sure the equation is BALANCED.
• Label the QUANTITIES GIVEN.• DRAW a DIMENSIONAL ANALYSIS • FRAME:
Grams starting
X FW starting, g
1 molestarting
Moles starting
Moles ending
1 mole ending
FW ending, g
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• Fill in the frame with the MOLES and FWs as indicated on the frame.
• Complete the math across the top of the frame, then across the bottom.
• Finally divide the TOP by BOTTOM and ROUND to SIGNIFICANT FIGURES.
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Practice Problem
• If 75.2 g of KClO3 decomposes, how many grams of O2 will be produced?
2 KClO3 2 KCl + 3 O2
75.2 g ? g
✔balanced✔balanced
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75.2g KClO3 =
FW KClO3
XX 122.55 g KClO3
122.55 g KClO3
1 moleKClO3
1 moleKClO3
2 moleKClO3
2 moleKClO3
3 moleO2
3 moleO2
1 moleO2
1 moleO2
31.998 gO2
31.998 gO2
FW O2FW O2
MoleRatioMoleRatio
______ g O2______ g O2
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75.2g KClO3 =
XX 122.55 g KClO3
122.55 g KClO3
1 moleKClO3
1 moleKClO3
2 moleKClO3
2 moleKClO3
3 moleO2
3 moleO2
1 moleO2
1 moleO2
31.998 gO2
31.998 gO2
7218.7488 g O2
____________________
245.1
7218.7488 g O2
____________________
245.1
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=29.45225 g ≈ 29.5 g O2
=29.45225 g ≈ 29.5 g O2
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MORE PRACTICE
• #1) If 75.2 grams of Calcium Sulfate are reacted with an unlimited amount of Sodium Phosphate, what mass of Calcium Phosphate will be formed according to the reaction:
• CaSO4 + Na3PO4 Ca3(PO4)2 + Na2SO4
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• #2) How many grams of Potassium are needed to form 125.6 grams of Potassium Carbonate according to the reaction below?
• K + Li2CO3 K2CO3 + Li