The Mole and Stoichiometry
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Transcript of The Mole and Stoichiometry
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The Mole and The Mole and StoichiometryStoichiometry
Chemistry gets Real….Chemistry gets Real….
Tough that isTough that is
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The “mole”The “mole”
A term for a certain number of A term for a certain number of something.something.
Brainstorm other counting words!Brainstorm other counting words! Dozen = Dozen = Pair = Pair = Gross = Gross =
A “mole” of something is A “mole” of something is 6.02 x 106.02 x 102323 of something of something..
602, 000, 000, 000, 000, 000, 000, 000602, 000, 000, 000, 000, 000, 000, 000
12
2
144
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Molecular WeightMolecular Weight
M.W. = M.W. = the the weightweight (in grams) of a (in grams) of a molemole of of substancesubstance
On your periodic tablesOn your periodic tables Round to the nearest tenthRound to the nearest tenth
Hydrogen is 1.00797 Hydrogen is 1.00797 1.0 g/mol 1.0 g/mol
Mole Weight is an INTENSIVE propertyMole Weight is an INTENSIVE property—doesn’t depend on amount—doesn’t depend on amount
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Try these MW’sTry these MW’s
CaCa 40.140.1
HH22
2 (1.0) = 2.02 (1.0) = 2.0
BaFBaF22
[137.3 + 2(19.0)] = 175.3[137.3 + 2(19.0)] = 175.3
MW of 2BaFMW of 2BaF22 is still 175.3 is still 175.3
mol
g
mol
g
mol
g
1 mole of Ca weighs
40.1 grams
1 mole of H2 weighs 2.0 grams
mol
g
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1 penny = 2.681 penny = 2.68
6 pennies =6 pennies = g g
6 pennies = 6 pennies =
coin
g
coin
g2.68
2.68 X 6 = 16.08
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Avogadro’s NumberAvogadro’s Number
NNAA = 6.02 x 10 = 6.02 x 102323 of of anythinganything
Avogadro (1776-1856)
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1 mole K = 1 mole K = gramsgrams
MW of potassium = MW of potassium =
1 dozen K = 1 dozen K = atoms atoms 1 mole K = atoms 1 mole K = atoms
mol
g39.1
39.10
12
6.02 x 1023
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MW of COMW of CO22 = = 3 moles of CO3 moles of CO22 = =
3 moles of CO3 moles of CO22 = ____ g/mol = ____ g/mol
MW of nitrogen gas = MW of nitrogen gas = NN22 (g) = (g) =
mol
g44.0
2 ( 14.0) = 28.0 mol
g
gramsmol
gmoles 00.1320.443
mol
g44.0
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Which elements exist as diatomic Which elements exist as diatomic molecules?molecules?
HH2 2 NN22 OO22 F F22 ClCl22 BrBr22 II22
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How Big Is The Mole?How Big Is The Mole? One mole of marbles would cover the entire One mole of marbles would cover the entire
Earth to a depth of fifty milesEarth to a depth of fifty miles One mole of hockey pucks would equal the One mole of hockey pucks would equal the
mass of the moon.mass of the moon. One mole of rice grains is more than the One mole of rice grains is more than the
number of grains of all crops grown since the number of grains of all crops grown since the beginning of time.beginning of time.
If one mole of pennies was divided up equally If one mole of pennies was divided up equally between all the people on Earth, you would between all the people on Earth, you would have enough money to spend a million have enough money to spend a million dollars every hour, 24 hours a day, for your dollars every hour, 24 hours a day, for your entire life. When you died, you would have entire life. When you died, you would have spent less than half of your riches.spent less than half of your riches.
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Lab 11Lab 11
FormulaFormula Mass (g)Mass (g) MW MW MolesMoles MoleculMoleculeses
AtomsAtoms
AgNOAgNO33 15.0015.00 169.9169.9 0.0880.088 5.3 x 5.3 x 10102222
2.7 x 2.7 x 10102323
KOHKOH 18.9818.98 56.156.1 0.340.34 2.0 x 2.0 x 10102323
6.0 x 6.0 x 10102323
COCO 47.0047.00 28.028.0 1.681.68 1.0 x 1.0 x 10102424
2.0 x 2.0 x 10102424
NaNa22SOSO44 185.00185.00 142.1142.1 1.301.30 7.8x 7.8x 10102323
5.4 x 5.4 x 10102424
HH22 1.001.00 2.02.0 0.500.50 3.0 x 3.0 x 10102323
6 x 106 x 102323
NaNa22SS 13.7613.76 78.178.1 0.180.18 1.1 x 1.1 x 10102323
3.3 x 3.3 x 10102323
NaOHNaOH 214.75214.75 40.040.0 5.375.37 3.2 x 3.2 x 10102424
9.6 x 9.6 x 10102424
PbPb 6.506.50 207.2207.2 0.0310.031 1.8 x 1.8 x 10102222
1.8 x 1.8 x 10102222
PbPb33(PO(PO44))
22
18.7518.75 811.6811.6 0.0230.023 1.4 x 1.4 x 10102222
1.8 x 1.8 x 10102323
NaClNaCl 62.2562.25 58.558.5 1.061.06 6.6 x 6.6 x 10102323
1.3 x 1.3 x 10102424
mol
g
÷MW X NA X#atoms
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Percent CompositionPercent Composition
A. Determined from Formulas (“Accepted A. Determined from Formulas (“Accepted Value”)Value”)
Is NaCl 50.0% Na by weight?Is NaCl 50.0% Na by weight?
NoNo, Na is 23.0 g/mole and Cl is 35.5 g/mole , Na is 23.0 g/mole and Cl is 35.5 g/mole
To Prove, % Na =To Prove, % Na =
%3.39100 X )235.35(
23
100 NaCl
Na X
MW
MW
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Percent CompositionPercent Compositionfrom Formulafrom Formula
% oxygen in CaCO% oxygen in CaCO33??
Grams of Mg in 4.00 grams of MgO?Grams of Mg in 4.00 grams of MgO?
O%0.48%9520.47 100 X (100.1)
(48)
)]16(30.121.40[
)16(3
Mg%3.60%2977.60)163.24(
3.24
gMgg 41.2)00.4(603.0
First: Calculate % Mg in MgO
Second: Calculate g Mg in 4.00 g MgO
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B. Experimental Percent CompositionB. Experimental Percent Composition FROM DATA (“Experimental Value”)FROM DATA (“Experimental Value”) 4.00g of Ag4.00g of Ag22O is O is decomposeddecomposed to yield 3.65g Ag. to yield 3.65g Ag.
The Experimental % = ? The Experimental % = ?
The Accepted % = ?The Accepted % = ?
Your Experimental Error?Your Experimental Error?
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Experimental % AgExperimental % Ag
Equation:Equation:
AgAg22O O
Experimental % Ag:Experimental % Ag:
4.00 g 3.65 g
%3.91%25.9100.4
65.3
g
g
Ag + O22 4
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True (Accepted) %AgTrue (Accepted) %Ag
%9.1%9333.1100 X 1.93
1.933.91 100 X
valueaccepted
value)accepted - valuealexperiment(
%1.93%097.93 100 X 231.8
(215.8)
]16)9.107(2[
)9.107(2
100 Ag
Ag
2
XOMW
MW
Percent Error?
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Empirical FormulaEmpirical Formula
Definition:Definition:The The simplestsimplest formula indicating the formula indicating the
mole ratiomole ratio of elements in a compound of elements in a compound Examples:Examples:
HH22OO22 HO HO CC66HH66CHCH NN22OO44?? COCO22 ? ?
NO2
CO2
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Empirical Formula STEPSEmpirical Formula STEPS
1.1. Change grams to molesChange grams to moles
2.2. Divide by the least # moles for a Divide by the least # moles for a RATIORATIO
3.3. Apply ratio to the formulaApply ratio to the formula
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Solving Empirical Formula—Solving Empirical Formula—determined from gram compositiondetermined from gram composition
A compound contains 0.90 g Ca and 1.60 A compound contains 0.90 g Ca and 1.60 g Clg Cl
Camoles 022.01.40
90.0
2Ca 022.0
Cl 045.0
moles
molesCaCl2
Clmoles 045.05.35
60.1
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Try This…Try This…
0.556 g Carbon and 0.0933 g Hydrogen0.556 g Carbon and 0.0933 g Hydrogen
molesC046.00.12
0556.0 molesH0933.0
1
0933.0
2C 046.0
H 0933.0
moles
molesCH2
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Why is the Empirical Formula a Why is the Empirical Formula a ratio of small WHOLE numbers?ratio of small WHOLE numbers?
Can’t have half of an atomCan’t have half of an atom Atoms combine as Atoms combine as wholewhole units units Shows the simplest way that atoms Shows the simplest way that atoms
can paircan pair
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What formula would this ratio give?What formula would this ratio give?
K = 0.26 molesK = 0.26 moles N = 0.25 molesN = 0.25 moles O = 0.78 molesO = 0.78 moles Yields an Empirical Formula of…Yields an Empirical Formula of…
KNOKNO33
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Try This: 70.5 % Fe and 29.5 % OTry This: 70.5 % Fe and 29.5 % O
___ moles Fe, ___ moles O___ moles Fe, ___ moles O
Assume 100g of substance:Assume 100g of substance:
Femolesiron
molgIrongof
26.19.55
5.70
1.26
1.84
Fe2O3
Omolesoxygen
molgOxygengof
84.10.16
5.29
1.26 moles 1.26 moles
FeO1.5X 2
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Try This: 40.0% CTry This: 40.0% C 6.7% H 53.3% O6.7% H 53.3% O
___ moles C, ___ moles H, ___ moles O___ moles C, ___ moles H, ___ moles O
Assume 100g of substance:Assume 100g of substance:
molesCcarbon
molggofcarbon
3.30.12
00.40
3.3 6.7 3.3
After dividing by the least moles yields:
CH2
O
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Why doesn’t the ratio of the % give Why doesn’t the ratio of the % give the empirical formula?the empirical formula?
Must account for differing Must account for differing massesmasses of of elements.elements.
Why does the ratio of the moles give Why does the ratio of the moles give the empirical formula?the empirical formula? The ratio of the # of atoms normalizes The ratio of the # of atoms normalizes
for mass differences.for mass differences.
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Molecular FormulasMolecular Formulas
Definiton: Definiton: Formula of an actual Formula of an actual compoundcompound
as it exists in molecules.as it exists in molecules. Benzene exists as CBenzene exists as C66HH6 6 not CH. not CH. Hydrogen Peroxide exists as HHydrogen Peroxide exists as H22OO2 2
not HO.not HO.
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Empirical Empirical FormulaFormula
MW MW EmpiricalEmpirical
MW MW MolecularMolecular
Molecular Molecular FormulaFormula
HOHO 34 g/mol34 g/mol
CHOClCHOCl22 200 200 g/molg/mol
CClNCClN22 226.5 226.5 g/molg/mol
H2O217 g/mol17 g/mol
X 2
100 g/mol100 g/mol
75.5 g/mol75.5 g/mol
CC22HH22OO22ClCl44
CC33ClCl33NN66
X 2
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Why is the M.W. needed to Why is the M.W. needed to determine the molecular formula?determine the molecular formula? Need M.W. of actual compound to find Need M.W. of actual compound to find
how many each type of atom is in a how many each type of atom is in a molecule.molecule.
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Stoichiometry – The Big LeaguesStoichiometry – The Big Leagues
A. Define:A. Define:Problem Solving involving mass-mass Problem Solving involving mass-mass relationships in chemical changesrelationships in chemical changes Ex. How many grams of rust are formed Ex. How many grams of rust are formed
when 12.00 g of Fe reacts with oxygen.when 12.00 g of Fe reacts with oxygen.
B. Must use B. Must use balancedbalanced equations for equations for the correct mole ratiosthe correct mole ratios
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C. CoefficientsC. Coefficients yield the mole yield the mole ratio!!!ratio!!!
22 H H22 + O + O22 22 H H22OO
2 : 12 : 1 : 2 : 2
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D. ExampleD. Example
4 Fe + 3 O4 Fe + 3 O22 2 Fe 2 Fe22OO33
4 : 3 : 24 : 3 : 2
If 4 moles of iron rust, If 4 moles of iron rust, moles of Fe moles of Fe22OO33 will form will form
If 8 moles of iron rust,If 8 moles of iron rust, moles of Femoles of Fe22OO33 will form will form4
2
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Solving Solving Mass-Mass Mass-Mass ProblemsProblems
1) Determine the mole ratio (from the balanced equation)
2) Convert grams to moles
3) Apply the mole ratio
4) Convert moles to grams
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28.00 g of iron yields 28.00 g of iron yields ? ? g of rust? g of rust?
4 Fe + 3 O4 Fe + 3 O22 2 Fe 2 Fe22OO33
28.00 g 28.00 g FeFe
0.50 moles0.50 moles
molgg
8.55
00.28
2:1
molesmol
g25.00.160
0.25 moles0.25 moles
40.00 g 40.00 g FeFe22OO33
? g Fe2O3
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36.00 g of water resulted from 36.00 g of water resulted from ? ? g of methane? g of methane?
CHCH44 + O + O22 CO CO22 + H + H22OO
36.00 g 36.00 g HH22OO
1.00 moles1.00 moles
gmol
gmole 00.160.161
1:2
moles
molgg
20.18
00.36
2.00 moles2.00 moles
16.00g of 16.00g of methanemethane
2 2
Balance
? g CH4
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Variation:Variation:12 moles of oxygen combusting will yield 12 moles of oxygen combusting will yield
how many grams of COhow many grams of CO22??
12 moles12 moles 2:1
molesmol
g60.44
6 moles6 moles
264.00 g 264.00 g COCO22
CHCH44 + O + O22 CO CO22 + H + H22OO2 2
? g CO2