MOLAR MASS What is molar mass? How do you calculate molar mass?
Chemical Reactions Unit Learning Goal #3: Determine the molar proportions in a chemical reaction and...
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Transcript of Chemical Reactions Unit Learning Goal #3: Determine the molar proportions in a chemical reaction and...
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Chemical Reactions Unit
Learning Goal #3: Determine the molar proportions in a chemical reaction and use them to predict the mass of product produced in a simple chemical reaction that goes to completion
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The MoleThe Mole
6.02 X 6.02 X 10102323
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STOICHIOMETRYSTOICHIOMETRYSTOICHIOMETRYSTOICHIOMETRY
- the study of the - the study of the quantitative quantitative aspects of aspects of chemical chemical reactions.reactions.
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The MoleThe Mole
OA counting unitOSimilar to a dozen, except instead
of 12, it’s 602 billion trillion 602,000,000,000,000,000,000,000
O6.02 X 1023 (in scientific notation)OThis number is named in honor of
Amedeo _________ (1776 – 1856)Amedeo _________ (1776 – 1856), who studied quantities of gases and discovered that no matter what the gas was, there were the same number of molecules present
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Just How Big is a Mole?Just How Big is a Mole?
O Enough soft drink cans to cover the surface of the earth to a depth of over 200 miles.
O If you had Avogadro's number of unpopped popcorn kernels, and spread them across the United States of America, the country would be covered in popcorn to a depth of over 9 miles.
O If we were able to count atoms at the rate of 10 million per second, it would take about 2 billion years to count the atoms in one mole.
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The MoleThe Mole
O1 dozen cookies = 12 cookiesO1 mole of cookies = 6.02 X 1023 cookies
O1 dozen cars = 12 carsO1 mole of cars = 6.02 X 1023 cars
O1 dozen Al atoms = 12 Al atomsO1 mole of Al atoms = 6.02 X 1023 atoms
Note that the NUMBER is always the same, but the MASS is very different!
Mole is abbreviated mol
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= 6.02 x 1023 C atoms
= 6.02 x 1023 H2O molecules
= 6.02 x 1023 NaCl “molecules”(technically, ionics are compounds not
molecules so they are called formula units)
6.02 x 1023 Na+ ions and
6.02 x 1023 Cl– ions
A Mole of ParticlesA Mole of Particles Contains 6.02 x 1023 particles
1 mole C
1 mole H2O
1 mole NaCl
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6.02 x 1023 particles
1 mole
or
1 mole
6.02 x 1023 particles
Note that a particle could be an atom OR a molecule!
Avogadro’s Number as Avogadro’s Number as Conversion FactorConversion Factor
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1. Number of atoms in 0.500 mole of Ala) 500 Al atoms
b) 6.02 x 1023 Al atomsc) 3.01 x 1023 Al atoms
2.Number of moles of S in 1.8 x 1024 S atomsa) 1.0 mole S atomsb) 3.0 mole S atomsc) 1.1 x 1048 mole S atoms
Learning CheckLearning Check
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Mole Ratios
OA mole ratio converts moles of one compound in a balanced chemical equation into moles of another compound.
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Example
Reaction between magnesium and oxygen to form magnesium oxide. ( fireworks)
2 Mg(s) + O2(g) 2 MgO(s)
Mole Ratios:2 : 1 : 2
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OThe Mass of 1 mole (in grams)
OEqual to the numerical value of the average
atomic mass (get from periodic table)
1 mole of C atoms = 12.0 g
1 mole of Mg atoms = 24.3 g
1 mole of Cu atoms = 63.5 g
Molar MassMolar Mass
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Other Names Related to Molar MassOther Names Related to Molar Mass
O Molecular Mass/Molecular Weight: If you have a single
molecule, mass is measured in amu’s instead of grams. But,
the molecular mass/weight is the same numerical value as 1
mole of molecules. Only the units are different. (This is the
beauty of Avogadro’s Number!)
O Formula Mass/Formula Weight: Same goes for
compounds. But again, the numerical value is the same.
Only the units are different.
OTHE POINT: You may hear all of these terms which mean the SAME NUMBER… just different units
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Prozac, C17H18F3NO, is a
widely used antidepressant
that inhibits the uptake of
serotonin by the brain. Find
its molar mass.
Learning CheckLearning Check
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molar mass
Grams Moles
Calculations with Molar MassCalculations with Molar Mass
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Aluminum is often used for the structure of light-weight bicycle frames. How many grams of Al are in 3.00 moles of Al?
3.00 moles Al ? g Al
Converting Moles and GramsConverting Moles and Grams
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1. Molar mass of Al 1 mole Al = 27.0 g
Al
2. Conversion factors for Al
27.0g Al or 1 mol Al
1 mol Al 27.0 g Al
3. Setup 3.00 moles Al x 27.0 g Al
1 mole Al
Answer = 81.0 g Al
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The artificial sweetener aspartame (Nutra-
Sweet) formula C14H18N2O5 is used to sweeten
diet foods, coffee and soft drinks. How many
moles of aspartame are present in 225 g of
aspartame?
Learning Check!Learning Check!
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Atoms/Molecules and GramsAtoms/Molecules and Grams
OSince 6.02 X 1023 particles = 1 mole AND
1 mole = molar mass (grams)OYou can convert atoms/molecules to moles
and then moles to grams! (Two step process)
OYou can’t go directly from atoms to grams!!!! You MUST go thru MOLES.
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molar mass Avogadro’s number Grams Moles particles
Everything must go through Moles!!!
CalculationsCalculations
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Atoms/Molecules and GramsAtoms/Molecules and Grams
How many atoms of Cu are present in 35.4 g of Cu?
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Learning Check!Learning Check!
How many atoms of K are present in 78.4 g of K?
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Learning Check!Learning Check!
What is the mass (in grams) of 1.20 X 1024 molecules of glucose (C6H12O6)?
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Learning Check!Learning Check!
How many atoms of O are present in 78.1 g of oxygen?
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Calculating Masses of Calculating Masses of Reactants and ProductsReactants and Products
O Balance the equationBalance the equation.. O Convert mass to moles. Convert mass to moles. O Set up mole ratios. Set up mole ratios. O Use mole ratios to calculate moles of Use mole ratios to calculate moles of
desired molecule. desired molecule. O Convert moles to grams or to particles, if Convert moles to grams or to particles, if
necessary.necessary.
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Working a Stoichiometry Working a Stoichiometry ProblemProblem
O 6.50 grams of aluminum reacts with an excess of oxygen. How many grams of aluminum oxide are formed.
1. Identify reactants and products and write the balanced equation.
4Al + 3O2 2Al2O3
O b. What are the reactants?O a. Every reaction needs a yield sign!O c. What are the products?O d. What are the balanced coefficients?
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Working a Stoichiometry ProblemWorking a Stoichiometry Problem
6.50 grams of aluminum reacts with an excessof oxygen. How many grams of aluminum oxide are formed?
4 Al + 3 O2 2Al2O3
=6.50 g Al
? g Al2O3
1 mol Al
26.98 g Al 4 mol Al
2 mol Al2O3
1 mol Al2O3
101.96 g Al2O3
6.50 x 2 x 101.96 ÷ 26.98 ÷ 4 =
12.3 g Al2O3
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