unit 6 stoichiometry. what exactly is stoichiometry? composition stoich – deals with mass...
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Unit 6 Stoichiometry
What Exactly Is Stoichiometry?
Composition stoich – deals with mass relationships of elements in compounds (review Ch 3)
Reaction stoich – deals with relationships between reactants and products
What You’ve Learned So Far…
•Unit Conversions•Naming Chemical Compounds•Writing Chemical Formulas •The Mole•Writing Chemical Equations •Balancing Chemical Equations
Mole Ratios•Conversion factor relating amount of moles of any two substances
Example(g)3O 4Al(s) (aq)O2Al 232
Al 4
OAl 2 32
32OAl 2
Al 4
Al 4
O 3 2
2
32
O 3
OAl 2
32
2
OAl 2
O 3
2O 3
Al 4
or
or
or
Molar Mass Ratios
Al2O3 – 101.96 g/mol
Al – 26.98 g/mol
O2 – 32.00 g/mol2
2
2
2
32
32
32
32
O g 00.32
O mol 1or
O mol 1
O g 00.32
Al g 26.98
Al mol 1or
Al mol 1
Al g98.26
OAl g 96.101
OAl mol 1or
OAl mol 1
OAl g 96.101
(g)3O 4Al(s) (aq)O2Al 232
Solving Stoichiometry
Problems
Must have:1. Correct molecular
formulas2. Balanced chemical
equation
Steps to Solving Problems
1. Write a balanced chemical equation
2. Identify information given in problem
3. Pick appropriate molar mass or mole ratio
4. Multiply numerators5. Multiply denominators
Reaction Stoichiometry
Mole-MoleMole-Mass or Mass-Mole
Mass-Mass
Type 1
• Given quantity and unknown quantity in moles
Quantity givengiven (in mol)
Quantity unknownunknown (in mol)
Stoichiometry Examples: Type 1 (mol-mol)Example 1: The combustion of 2.19
moles propane (C3H8) produces how many moles carbon dioxide?
Example 2: 41.8 mol lithium hydroxide is combined with carbon dioxide to produce lithium carbonate and liquid water. How much water is produced from this reaction?
Type 2
• Given amount is in moles and unknown is mass in grams
Amount givengiven (in mol)
amount unknownunknown (in mol)
mass unknownunknown (in g)
Stoichiometry Examples: Type 2 (mol-mass)
Example 3:In photosynthesis, plants use energy
from the sun to produce glucose C6H12O6, and oxygen from the reaction of carbon dioxide and water. What mass, in grams, of glucose is produced when 3.00 mol of water react with carbon dioxide?
Type 3
• Given is amount in grams and unknown is amount in moles
mass givengiven (in g) amount givengiven (in mol)
amount unknownunknown (in mol)
Stoichiometry Examples: Type 3 (mass-mol)NaHCO3 and Mg(OH)2 are both used as
antacids – which is more effective per gram?
Example 4: 1.00 g NaHCO3 reacts with hydrochloric acid to produce sodium chloride, water, and carbon dioxide
Example 5: 1.00 g Mg(OH)2 reacts with hydrochloric acid to produce magnesium chloride and water
Stoichiometry Examples:Type 3 (mol-mass)
Example 6What mass of carbon dioxide, in
grams, is needed to react with 3.50 mol of water in the photosynthetic reaction?
ObjectiveIII.A.3(i) – Use chemical equations
to perform basic mole-mole, mass-mass, and mass-mole computations for chemical reactions
Type 4
• Given is mass in grams and unknown is mass in grams
mass givengiven (in g) amount givengiven (in mol)
amount unknownunknown (in mol) mass unknownunknown (in
g)
Stoichiometry Examples:Type 4 (mass-mass)
Example 7Tin (II) fluoride is used in some
toothpastes. It is made by the reaction of tin with hydrogen fluoride according to the following equation.
Sn(s) + 2HF SnF2(s) + H2(g)
How many grams of SnF2 are produced from the reaction of 30.00 g of HF with Sn?
Limiting Reagents
III.A.3(j) – identify limiting reagents and use this information when solving stoichiometry problems
What is a “limiting reagent”?
• The reactant that is completely used up first in a chemical reaction
How to Find the Limiting Reagent
1. Analyze the question2. Identify the given
information3. Write a balanced chemical
reaction4. Convert given information of
Reactant 1 to Product A5. Convert given information of
Reactant 2 to Product A
Theoretical Yield
III.A.3(k) – compute theoretical yield, actual (experimental) yield, and percent yield
III.A.3(l) – calculate percent error and analyze experimental errors that affect
percent error
Theoretical Yield
Using the limiting reagent to calculate the amount of product produced is called the theoretical yield
This is how much product could be made if the limiting reactant was totally consumed
Experimental Yield
Also called the actual yield
The amount of product actually collected in the laboratory is called the experimental yield
Percent Yield
yieldpercent 100yield ltheoretica
yield actual
Example – Limiting ReactantAluminum reacts with chlorine gas to
form aluminum chloride.
In a certain experiment, 10.0 g of aluminum is reacted with 35.0 g of chlorine gas.
What mass of aluminum chloride will be produced, assuming a complete reaction?
What mass of which reactant is left after the reaction?
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