Download - Chapter 10 Chemical Quantities
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Chapter 10 “Chemical Quantities”
You will need a
calculator for this
chapter!
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Section 10.1 p. 287 The Mole: A Measurement of
Matter
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How do we measure items?
You can measure mass,
volume,
or count pieces
We measure mass in grams
We measure volume in liters
We count pieces in MOLES
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Other Ways to Measure Amount
Pair: 1 pair of socks = 2 socks
Dozen: 1 dozen donuts = 12 donuts
Gross: 1 gross of pencils = 144 pencils (12 dozen)
Ream: 1 ream of paper = 500 sheets of paper
Guided Practice Problem p. 289
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Practice Problem #2 pg. 289
• Assume 2.0 kg of apples is 1 dozen and
that each apple has 8 seeds. How
many apple seeds are in 14 kg of
apples? (work INDEPENDENTLY to solve)
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What is the mole?
Not this kind of mole!
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Moles (abbreviated mol) Derived from German word
molekül (molecule)
SI measurement of an amount
1 mole = 6.02 x 1023 of representative particles, or…..
# of carbon atoms in exactly 12 g of Carbon-12 isotope
Called Avogadro’s number
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What are Representative Particles?
(Table 10.1 p. 290)
The smallest pieces of a substance:
1) molecular cmpd - molecule
2) ionic cmpd - formula unit (made
of ions)
3) element: is the
• Remember the 7 diatomic elements?
(made of molecules) BrINClHOF
H2 N2 O2 F2 Cl2 I2 Br2
atom
Guided Practice Problem #3 p. 291
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Mole Video 3:49
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Quick Quiz • How big is a mole?
• If everyone in the world got a mole of pennies, how much $ would every person have?
• If you stacked a mole of paper how many times would it go from the Earth to the moon?
• How long would it take for every person in the world to eat through a mole of marshmellows?
6.02 x 1023
1 trillion bucks $1,000,000,000,000
80 billion times 80,000,000,000
40,000,000 years w/o a bathroom break!
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Consider these questions:
• How many oxygen atoms in the following?
CaCO3
Al2(SO4)3
• How many ions in the following?
CaCl2
NaOH
Al2(SO4)3
3 atoms of oxygen
12 (3 x 4) atoms of oxygen
3 total ions (1 Ca2+ ion and 2 Cl1- ions)
2 total ions (1 Na1+ ion and 1 OH1- ion)
5 total ions (2 Al3+ + 3 SO42- ions)
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The Mass of a Mole of an Element
Atomic mass of element (mass
of 1 atom) expressed in amu
- atomic masses - relative
masses based on mass of C-12
(12.0 amu)
- 1 amu is 1/12 mass of C-12
atom
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Molar Mass…. = mass of 1 mol of element in grams
(periodic table)
12.01 grams C has same # particles
as 1.01 g H & 55.85 g Fe
12.01 g C = 1 mol C
1.01 g H = 1 mol H
55.85 g Fe = 1 mol Fe
All contain
6.02 x 1023
atoms
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Molar Mass Practice Problems
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What about compounds? 1 mol of H2O molecules has 2 mol
of H atoms & 1 mol of O atoms (think
of a compound as a molar ratio)
To find mass of 1 mol of a cmpd:
odetermine # moles of elements present
oMultiply # times their mass (from periodic table)
oadd up for total mass
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Calculating Molar Mass
Calculate molar mass of
magnesium carbonate, MgCO3.
24.3 g + 12.0 g + 3 x (16.00 g) = 84.3 g
So, 84.3 g = molar mass for MgCO3
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Section 10.2 p. 297
Mole-Mass and Mole-Volume Relationships
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Molar Mass Molar mass - generic term for
mass of 1 mol of any substance
(expressed in grams/mol)
Same as:
1) Gram Molecular Mass (for molecules)
2) Gram Formula Mass (ionic compounds)
3) Gram Atomic Mass (for elements)
o molar mass is more broad term than
these other specific masses
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Examples Calculate the molar mass of:
Na2S
N2O4
C
Ca(NO3)2
C6H12O6
(NH4)3PO4
= 78.05 g/mol
= 92.02 g/mol
= 12.01 g/mol
= 164.10 g/mol
= 180.12 g/mol
= 149.12 g/mol
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Molar Mass is… # of g in 1 mol of atoms,
formula units, or molecules
Make conversion factors
from these
- To change btwn g of
cmpd and mol of cmpd
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Using the Mole Roadmap
How many moles is 5.69 g
of NaOH?
0.142 mol NaOH
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The Mole-Volume Relationship
gases - hard to determine mass
how many moles of gas?
2 things affect gas V:
a) Temp & b) Pressure
compare all gases at = temp &
pressure
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Standard Temperature and Pressure
0ºC & 1 atm pressure
- abbreviated “STP”
At STP, 1 mol of any gas has
V of 22.4 L
- Called molar volume
1 mol of any gas at STP = 22.4 L
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Mole Day
Celebrated on
October 23rd from 6:02
am until 6:02 pm
(6:02 on 10-23)
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Density of a gas D = m / V (density = mass/volume)
- for gas units are: g / L
find density of a gas at STP if
formula known
You need: 1) mass and 2) volume
Assume 1 mol, so mass is molar
mass (from periodic table)
At STP, V = 22.4 L
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Another way: If given density, find molar mass of gas
Assume 1 mol at STP, so V = 22.4 L
modify: D = m/V to show:
“m” will be mass of 1 mol, given 22.4 L
What is molar mass of a gas with
density of 1.964 g/L?
How about a density of 2.86 g/L?
= 44.0 g/mol
64.0 g/mol
m = D x V
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Summary • all equal:
a) 1 mole
b) molar mass (in grams/mol)
c) 6.02 x 1023 representative particles (atoms, molecules, or formula units)
d) 22.4 L of gas at STP
make conversion factors from these 4 values (p.303)
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Notice all conversions must go through the MOLE!
Copy this conversion map into your notes!
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Section 10.3 p. 305
Percent Composition and Chemical Formulas
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All percent problems:
part
whole 1) Find mass of each element,
2) Divide by total mass of cmpd; & x 100
x 100 % = percent
%mass of element = mass of element
x 100% mass of cmpd
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% composition from mass Calculate the percent composition
of a compound that is made of 29.0
grams of Ag with 4.30 grams of S.
29.0 g Ag
33.3 g total X 100 = 87.1 % Ag
4.30 g S
33.3 g total X 100 = 12.9 % S
Total = 100 %
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% comp from the chemical formula
If we know formula, assume
you have 1 mole,
Subscripts used to calculate
mass of each element in 1
mole of cmpd
sum of masses is molar mass
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% composition as conversion factor
We can also use % as
conversion factor to calculate
# grams of element in cmpd
Calculate % C in C3H8
What is mass of C in 82.0 g sample
of propane (C3H8) 67.1 g C
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What is an Empirical Formula?
• Like ingredients for recipe –
double recipe, you double each
ingredient, but ratio of
ingredients stays same
• Empirical formula: lowest
whole number ratio of atoms
in cmpd
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Calculating Empirical Find lowest whole number ratio
C6H12O6
CH4N
A formula is not just ratio of atoms, it
is also ratio of moles
1 molecule of CO2 = 1 atom of C
and 2 atoms of O
1 mol of CO2 = 1 mol C and 2 mol O
= CH2O
= this is already the lowest ratio.
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Calculating Empirical get a ratio from % composition
1) Assume you have a 100 g sample - the percentage become grams (75.1% = 75.1 grams)
2) Convert grams to moles.
3) Find lowest whole number ratio by
dividing each # of moles by
smallest value
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Example Calculate empirical formula of
cmpd composed of 38.67 % C,
16.22 % H, and 45.11 %N. Assume 100 g sample, so
38.67 g C x 1mol C = 3.22 mole C 12.0 g C
16.22 g H x 1mol H = 16.22 mole H 1.0 g H
45.11 g N x 1mol N = 3.22 mole N 14.0 g N
Now divide each value by the smallest value
CH5N
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Example
The ratio is 3.22 mol C = 1 mol C
3.22 mol N 1 mol N
The ratio is 16.22 mol H = 5 mol H
3.22 mol N 1 mol N
= C1H5N1 which is = CH5N
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What is a Molecular Formula?
• Molecular formula: true # of atoms of
each element in formula of cmpd
• molecular cmpds only
• Example: molecular formula for
benzene is C6H6 (note that
everything is divisible by 6)
• Therefore, empirical formula = CH (the
lowest whole number ratio)
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Formulas (continued)
ionic compounds ALWAYS
empirical (cannot be reduced).
Examples:
NaCl MgCl2 Al2(SO4)3 K2CO3
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Formulas (continued)
Formulas for molecular compounds
MIGHT be empirical (lowest whole
number ratio).
Molecular:
H2O
C6H12O6 C12H22O11
Empirical:
H2O
CH2O C12H22O11
(Correct formula)
(Lowest whole
number ratio)
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Empirical to molecular Since empirical formula is lowest
ratio, the actual molecule weighs more
Molar mass
Empirical formula mass
whole # to increase
each coefficient in
empirical formula
=
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Empirical and Molecular Formulas
3:29