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Moles, Composition, Stoichiometry, and Reactions
Bring To Class EVERYDAY
Reference Table
Calculator
What’s a Mole?
What’s a Mole?
Humans have trouble with BIG amounts Picture something that has a mass of
80 MILLION milligrams Tough, eh?
Now picture something that has a mass of 80 kilograms
That’s the mass of an average Human We use metric prefixes to make
understanding big numbers easier
What’s a Mole?
Humans also use “representative terms” to stand for big numbers instead of using prefixes: Dozen = 12 Gross = 144 Pair = 2 Fortnight = 14 days Ream = 500 sheets of paper
What’s a Mole?
A “mole” simply is a word that represents a number Mole = 602,000,000,000,000,000,000,000
Do you really want to remember that many zeros?
6.02 x 1023
Much simpler using scientific notation A man named Amendeo Avogadro
discovered this useful number so we usually call it “Avagadro’s Number”
What can a mole represent? There can be a mole of:
“Particles” Atoms Ions Molecules Formula Units
We could use Mole for other things like: Eggs, doughnuts, chairs, people
It just doesn’t make sense to; it’s not a useful counting number for those things
Mole Practice
# “particles” = # of moles X 6.02 x 1023
Must be memorized How many atoms are there in:
.5 moles of Sodium? 2 moles of Carbon? 10 moles of Helium?
3.01 x 1023 atoms
1.204 x 1024 atoms
6.02 x 1024 atoms
What Else is Avogadro’s Number Useful for?
The Gram Atomic Mass for each element defined as the mass of one mole of atoms of that element. The mass of one mole of hydrogen atoms
(602,000,000,000,000,000,000,000 atoms) is ONLY 1g!
The Gram Formula Mass is defined as the mass of one mole of a molecule (Covalent) or formula unit (Ionic).
How Many Atoms Are In…
It is important to be able to determine how many atoms of each element are in a formula. H2O H - ____ O - ____ NaOH Na - ____ O - ____ H - ____ MgSO4 Mg - ____ S - ____ O - ____ Ca(CN)2 Ca - ____ C - ____ N - ____ Fe3(PO4)2 Fe - ____ P - ____ O - ____
2
1
1
1
3
1
1 1
1 4
2 2
2 8
Practice Determine the mass of 1 mole of the
following: (ROUND TO THE NEAREST TENTH) Hydrogen atoms Carbon atoms *Hydrogen molecules Oxygen molecules Sodium Chloride Iron (III) Sulfide Magnesium Sulfate Manganese (IV) Carbonate
1.0g12.0g2.0g
32.0g58.5g207.9g120.4g174.9g
•Remember the “Diatomic Elements”•Br I N Cl H O F•7-Up
What If There Isn’t Exactly 1 Mole?
TABLE - T # of moles = given mass (g)
Gram Formula Mass
Aka “Molar Mass”Aka “GFM”
Practice
If there is 80g of NaOH, how many moles are there? # moles = ? Given Mass = 80g GFM = 23 + 16 + 1 = 40g/mole # moles = 80g ÷ 40g # moles = 2
More Practice How many moles are there in the
following? 29.25 g NaCl 128 g O2
2.25 g H2O
What is the mass of the following? 2 moles MgCl2 8.5 moles HCl .11 moles Fe(OH)3
0.5 moles4.0 moles.125 moles
190.6 g310.25 g11.75 g
These are TOUGH!
# “particles”= # of moles X 6.02 x 1023
How many molecules are there in 30 g of sodium hydroxide?
What is the mass of 5 x 1023 molecules of Iodine?
# of moles = given mass (g)Gram Formula
Mass
4.5 x 1023 molecules
211 g
Percent Composition
By Mass, how much of each element is contained in a chemical?
How much of a chemical’s mass comes from one element opposed to another?
TABLE - T
% Composition By Mass = Mass of Part x 100 Mass of Whole
Percent Composition From A FORMULA
Must be able to calculate the GFM GFM = Mass of Whole
Find the percent by mass of each element in Glucose C6H12O6
C – 6 x 12 = 72 H – 12 x 1 = 12 O – 6 x 16 = 96 TOTAL GFM = 180
Percent Composition From A FORMULA
Mass of Part = GAM of each element multiplied by how many of each element there is. C = 72 H = 12 O = 96
( ÷ 180) x 100 = 40.0 %( ÷ 180) x 100 = 6.7 %( ÷ 180) x 100 = 53.3 %
Practice
Find the Percent composition of each element in the formula (NH4)HCO3. Total Mass – 79 g N – 17.7 % H – 6.3 % C – 15.2 % O – 60.8 %
Percent Composition From DATA
A 5.0 gram sample of C6H12O6
contains 1.99g of carbon, .33g of hydrogen, and 2.6g of oxygen. Calculate the % composition of each element.% C = 1.99g
5.0g x 100= 39.8%
% H = .33g 5.0g
x 100= 6.6%
% O = 2.6g 5.0g
x 100 = 52%
Percent Error
Finding % composition from the formula of a Substance is the Accepted value
Finding % composition from data is the Measured value (experimental value)
You can then find the % error
Percent Error
Using the previous glucose examples, find the students % error for Carbon.Accepted % C = 40.0%
Measured % C = 39.8%
% error = 39.8 – 40.0 40.0
x 100= -.5%
Hydrates
Some salts contain water molecules as a part of their structure.
The crystal lattice structure actually have water molecules as a part of them.
These are called hydrates.
Hydrates
Example: Cobalt (II) chloride hexahydrate CoCl2 • 6H2O
This means there is a CoCl2 with 6 waters attached
Percent Water in Hydrates
CoCl2 • 6H2O Mass of Part = Mass of Whole = % By Mass = 108 ÷ 237.9 x 100 = 45.4 % H2O
% Composition By Mass = Mass of Part x 100 Mass of Whole
Practice
Find the % water in the hydrate AlCl3 • 6H2O 44.7 % water
Molecular v. Empirical Formula
Empirical Formula The simplest integer ratio in which
atoms combine to form a compound. Reduce to simplest terms
Ionic compounds are always written as an empirical formula
Covalent molecules are not
Converting Molecular Formulas to Empirical Formulas
Molecular formula
C6H12O6 MgCl2 NO2 N2O4 C3H6O3
Empirical FormulaCH2O
MgCl2NO2
NO2
CH2O
Finding Molecular Formula Using Empirical Formula
A Molecule has a GFM of 138 and an empirical formula of NO2. What is the molecular formula?
Practice
A compound has a empirical formula of CH2 and a GFM of 84 g/mole. What is the molecular formula?
Reactants Products
yields, gives, or reacts to produce
Chemical Reactions
Word Equation
Iron + Oxygen Iron (III) Oxide
Skeleton Equation
Chemical equation that does not indicate the relative amounts of reactants and products
Fe(s) + O2(g) Fe2O3(s)
Practice
Word Equationlead (II) nitrate + sodium iodide lead (II) iodide + sodium nitrate
Skeleton Equation
Pb(NO3)2 + NaI
PbI2 + NaNO3
Symbols used in Chemical Equations
Symbol
Explanation
+ Used to separate two reactants or two products.
“Yields,” separates reactants from products.
Used in place of for reversible reactions.
(s), (l), (g)Designates reactants and products are in the solid, liquid, or gaseous state. Placed after the formula as a subscript.
(aq)Designates reactants or product as an aqueous solution; the substance is dissolved in water. Placed after the formula as a subscript.
Indicates that heat is supplied to the reaction.
A formula written above or below the yield sign indicates its use as a catalyst (in this case, platinum).
Heat
Pt
Balancing Chemical Equations
Balanced Equations Law of Conservation of Mass
Atoms can’t be created or destroyed All the atoms we start with we must end up
with A balanced equation has the same number
of atoms of each element on both sides of the equation.
Balancing Chemical Equations
1. Start with skeleton equation2. Use coefficients to balance the
equation (Conservation of Mass) coefficients represent moles
3. Make sure you have the same number of moles of each element on both sides of the arrow
___H2(g) + ___ O2(g) ___H2O(l)
Example
Make a table to keep track of where you are at
R PH
O
2
2
2
1Need twice as much O in the product
2Changes the OAlso changes the H
4
Need twice as much H in the reactant
2
Recount
4
The equation is balanced, has the same number of each kind of atom on both sides
H2(g) + O2(g) H2O(l)2
This is the answer
Not this
Tricky Regents Exam Question
Sometimes the Regents likes to be tricky with their questions.
What is the sum of the coefficients when the following equation is properly balanced?
2H2(g) + O2(g) H2O(l)2
5
+
___ Fe(s) + O2(g) Fe2O3(s)
R P
Fe
O
Fe
O
1
2
2
3
4
6
4
6
4 3 2
Practice: Balance Equations with Coefficients
__Pb(NO3)2 + __NaI __PbI2 + __NaNO3
__N2 + __H2 __NH3
__Fe + __H2SO4 __Fe2(SO4)3 + __H2
__SnO2 + __H2 __Sn + __H2O
__SeCl6 + __O2 __ SeO2 + __Cl2
1 2 1 2
1 3 2
2 1 33
22 11
311 1
Balancing Combustion Equations
Combustion is when there is a “hydrocarbon” reacting with oxygen (O2) Save Oxygen for LAST!!!
__C2H6 + __O2 __H2O + __CO2R P
C
H
O
C
H
O
2
6
2
1
2
3
2
2
5
3
6
77
3.5?
Coefficients Must BeWhole Numbers!
1 4672
44
1212
1414
Combustion Practice
__C4H10 + __O2 __CO2 + __H2O
__C5H12 + __O2 __CO2 + __H2O
__C3H6 + __O2 __CO2 + __H2O
__C4H6 + __O2 __CO2 + __H2O
2 13 8 10
1 8 5 6
2 9 6 6
2 11 8 6
Five Types of Reactions Synthesis Decomposition Single-Replacement Double-Replacement Combustion
Synthesis Reactions
A chemical change in which two or more substances react to form a single new substance.
Identified by having only ONE PRODUCT Example:
2 Bread + Mayo + 2 Turkey Sandwich Robert + Grace A Couple A + B AB 2Mg(s) + O2(g) 2MgO(s)
Synthesis Reaction
2Mg(s) + O2(g) 2MgO(s)
Mg
O
O
Mg
Decomposition Reaction A chemical change in which a single
compound breaks down into two or more simpler products.
Identified by having only ONE REACTANT Example:
Old Car Transmission + Doors + Radio +… AB A + B 2HgO(s) 2Hg(l) + O2(g)
Decomposition Reaction2HgO(s) 2Hg(l) + O2(g)
O OHg Hg
Single-Replacement Reaction A chemical change in which one
element replaces a second element in a compound.
Identified by having an element and a compound on each side of the reaction arrow.
Example: 2 people dancing and another cuts in A + BC AB + C 2K(s) + Ca(NO3)2(aq) 2KNO3(aq) + Ca(s)
Single-Replacement Reaction
2K(s) + Ca(NO3)2(aq) 2KNO3(aq) + Ca(s)
Metals replace metals in compounds
Nonmetals replace nonmetals in compounds
F2(g) + 2KCl(aq) 2KF(aq) + Cl2(g)
Na + KCl K + NaCl
Na K Cl
F2 + 2 LiCl 2 LiF + Cl2
F
Li Cl
FLi Cl
Li
Li
Reference Table J Activity Series
Only more active metals will replace less active metals in a compound.
Only more active nonmetals will replace less active nonmetals in a compound.
Table - J
Single-Replacement Reaction
Predict whether the following single-replacement reactions will occur. If so, predict products and balance equation.
Na + ZnCl2 I2 + KCl Br2 + NaI Mg + BaCl2
2NaCl + ZnNo Rxn
2NaBr + I2
No Rxn
2
2
Double-Replacement Reaction A chemical change involving an
exchange of positive ions between two compounds.
Identified by having two compounds on each side of the reaction arrow.
Example: AB + CD AD + CB The Show “Wife Swap” 3NaOH + FeCl3 Fe(OH)3 + 3NaCl
3NaOH + FeCl3 Fe(OH)3 + 3NaCl
Na+ O- H+
Na+ O- H+
Na+ O- H+
Fe3+
Cl-
Cl-
Cl-
Combustion
Combustion
An organic molecular compound that combines with oxygen to produce water and carbon dioxide Organic Molecules contain CARBON
and HYDROGEN
C3H8 + 5O2 4H2O + 3CO2
O O
O O
O O
O O
O O
CC
C
Dimensional Analysis
Using ratios to convert one unit into another. How many minutes = 1 year? Ratios we know:
1 year has 365 days 1 day has 24 hours 1 hour has 60 minutes
These are called “Conversion Factors”
Using Conversion Factors
1 yearX
365 days
1 YearX
24 hours
1 DayX
60 min.
1 hour=
1 year has 365 days1 day has 24 hours
1 hour has 60 minutes
525,600 min.
How many seconds old are you?
16 and 1 month = 16.08 years 16 and 2 months = 16.17 years 16 and 3 months = 16.25 years 16 and 4 months = 16.33 years 16 and 5 months = 16.42 years 16 and 6 months = 16.5 years 16 and 7 months = 16.58 years 16 and 8 months = 16.67 years 16 and 9 months = 16.75 years 16 and 10 months = 16.83 years 16 and 11 months = 16.92 years
15 years old = 473,040,000 seconds
17 years old = 536,112,000 seconds
16 years old = 504,576,000 seconds
Conversion Factors You Might Not Be as Familiar With as I am Harry Potter’s Wand Cost 7
Galleons How many Knuts did it cost? What! You don’t know how
many Knuts are in a Galleon??? 1 Galleon = 17 Sickles 1 Sickle = 29 Knuts 3,451
Stoichiometry
Stoichiometry deals with ratios between Reactants and Products.
Pb(NO3)2 + 2 NaI PbI2 + 2 NaNO3
The ratio of Pb(NO3)2 to PbI2 is _____ The ratio of Pb(NO3)2 to NaNO3 is _____ The ratio of NaI to PbI2 is _____ The ratio of NaI to NaNO3 is _____ or _____
1:1
1:2
2:1
1:12:2
Stoichiometry
Pb(NO3)2 + 2 NaI PbI2 + 2 NaNO3
This means (if enough of the other reactant is present) for every:
1 mole of Pb(NO3)2 reacted, 1 mole of PbI2 is produced 1 mole of Pb(NO3)2 reacted, 2 moles of NaNO3 are
produced 2 moles of NaI reacted, 1 mole of PbI2 is produced 2 moles of NaI reacted, 2 mole of NaNO3 are
produced
Using Stoichiometry Ratios
Pb(NO3)2 + 2 NaI PbI2 + 2 NaNO3 If 2 moles of Pb(NO3)2 are reacted with
excess NaI, how many moles of NaNO3 are produced?
4 moles If 1 mole of NaI is reacted with excess
Pb(NO3)2, how many moles of PbI2 are produced?
0.5 moles
Using Dimensional Analysis with Stoichiometry
2 C4H6 + 11 O2 8 CO2 + 6 H2O These ratios look tougher to do mental math
with If 7 moles of oxygen are reacted with excess
C4H6, how many moles of CO2 are produced?
7 moles O2X
8 moles CO2
11 moles O2
= 5.09 moles CO2
Practice:
2 C4H6 + 11 O2 8 CO2 + 6 H2O What is the minimum # of moles of C4H6 that
are needed to produce 17 moles of H2O?
How many moles of CO2 are produced when 9.5 moles of C4H6 are reacted with excess O2?
5.67 moles C4H10
38 moles CO2
17 moles H2O X
2 moles C4H6
6 moles H2O=
9.5 moles C4H6 X
8 moles CO2
2 moles C4H6=
MASS Moles
2 H2 + O2 2 H2O How many moles of water are produced if 8 grams
of oxygen are reacted with excess hydrogen?
8 grams O2X
1 moles O2
32 grams O2
= 0.5 moles H2OX2 moles
H2O
1 moles O2
Practice: 2 C4H10 + 13 O2 8 CO2 + 10 H2O
How many moles of CO2 are produced when 15 g C4H10 are reacted with excess oxygen?
How many moles of H2O are produced when 123 g of oxygen are reacted with excess C4H10?
What is the mass of CO2 produced when 5 moles of C4H10 are reacted with excess oxygen?
15 grams C4H10
X1 moles C4H10
58 grams C4H10
= 1.03 moles CO2X8 moles CO2
2 moles C4H10
123 grams O2
X1 moles O2
32 grams O2
= 2.97 moles H2OX10 moles H2O
13 moles O2
5 moles C4H10
X8 moles CO2
2 moles C4H10
= 880 grams CO2X44 grams CO2
1 moles CO2
