chapter 10 chemical quantities
TRANSCRIPT
Chapter 10 “Chemical Quantities”
You will need a
calculator for this
chapter!
Section 10.1 p. 287 The Mole: A Measurement of
Matter
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
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
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)
What is the mole?
Not this kind of mole!
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
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
Mole Video 3:49
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!
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)
Practice problems
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
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
Molar Mass Practice Problems
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
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
Section 10.2 p. 297
Mole-Mass and Mole-Volume Relationships
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
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
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
Using the Mole Roadmap
How many moles is 5.69 g
of NaOH?
0.142 mol NaOH
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
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
Practice Examples
Mole Day
Celebrated on
October 23rd from 6:02
am until 6:02 pm
(6:02 on 10-23)
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
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
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)
Notice all conversions must go through the MOLE!
Copy this conversion map into your notes!
Section 10.3 p. 305
Percent Composition and Chemical Formulas
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
% 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 %
% 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
% Composition Examples
% 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
% Composition 4:15
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
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.
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
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
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
Practice Problem 36 p. 310
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)
Formulas (continued)
ionic compounds ALWAYS
empirical (cannot be reduced).
Examples:
NaCl MgCl2 Al2(SO4)3 K2CO3
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)
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
=
Empirical and Molecular Formulas
3:29