This preview shows page 1. Sign up to view the full content.
Unformatted text preview: Chapter 10
Chemical Quantities
Chemical
or How you measure how much?
How
You can measure mass,
You
s or volume,
s or you can count pieces.
s We measure mass in grams.
s We measure volume in liters.
s s We count pieces in MOLES.
We
MOLES. Moles
Moles
s Defined as the number of carbon
Defined
atoms in exactly 12 grams of carbonatoms
12. 1 mole is 6.02 x 1023 particles.
s Treat it like a very large dozen
s s 6.02 x 1023 is called Avogadro's
number.
number. Representative particles
Representative
The smallest pieces of a substance.
s For an element it is an atom.
For
atom
– Unless it is diatomic
s For a molecular compound it is a
For
molecule.
molecule
s For an ionic compound it is a
For
formula unit.
formula
s Conversion factors
Conversion
Used to change units.
s Three questions
– What unit do you want to get rid of?
– Where does it go to cancel out?
– What can you change it into?
s Calculation question
Calculation
s How many molecules of CO2 are the in
4.56 moles of CO2 ?
4.56 Calculation question
Calculation
s How many moles of water is 5.87 x 10 22
molecules?
molecules? Calculation question
Calculation
s How many atoms of carbon are there in
How
1.23 moles of C6H12O6 ?
1.23 Measuring Moles
Measuring
The amu was one twelfth the mass of a
The
carbon 12 atom.
carbon
s Since the mole is the number of atoms
Since
in 12 grams of carbon12,
in
s the decimal number on the periodic
the
table is
table
– The mass of the average atom in
The
amu
amu
– the mass of 1 mole of those atoms in
the
grams.
grams.
s Gram Atomic Mass
Gram
The mass of 1 mole of an element in
The
grams.
grams.
s 12.01 grams of carbon has the same
12.01
number of atoms as 1.01 grams of
hydrogen and 55.85 grams of iron.
hydrogen
s We can write this as
We
12.01 g C = 1 mole
s We can count things by weighing
We
them.
them.
s Examples
Examples
s How much would 2.34 moles of
How
carbon weigh?
carbon Examples
Examples
s How many moles of magnesium in
How
4.61 g of Mg?
4.61 Examples
s How many atoms of lithium in 1.00 g
How
of Li?
of Examples
s How much would 3.45 x 1022 atoms
of U weigh?
of What about compounds?
What
in 1 mole of H2O molecules there are
molecules
two moles of H atoms and 1 mole of
O atoms
atoms
s To find the mass of one mole of a
To
compound
– determine the moles of the
determine
elements they have
elements
– Find out how much they would
Find
weigh
weigh
– add them up
s What about compounds?
What
s What is the mass of one mole of CH4? 1 mole of C = 12.01 g
s 4 mole of H x 1.01 g = 4.04g
s s 1 mole CH4 = 12.01 + 4.04 = 16.05g Molar Mass
Molar
s The mass of 1 mole s What is the molar mass of Fe2O3? 2 moles of Fe x 55.85 g = 111.70 g
s 3 moles of O x 16.00 g = 48.00 g
s The GFM = 111.70 g + 48.00 g = 159.70g
s Calculate the molar mass of the
following
following
s C6H12O6 s (NH4)3PO4 Using Molar Mass
Using
Finding moles of compounds
Counting pieces by weighing Molar Mass
Molar
The number of grams in 1 mole of
The
atoms, formula units, or molecules.
atoms,
s We can make conversion factors
We
from these.
from
s To change grams of a compound to
To
moles of a compound.
moles
s Or moles to grams
s For example
For
s How many moles is 5.69 g of NaOH? 5.69 g 1 mole 40.00 g q need to change grams to moles
q for NaOH
q 1mole Na = 22.99g 1 mol O = 16.00 g
1 mole of H = 1.01 g
q 1 mole NaOH = 40.00 g For example
For
How many moles is 5.69 g of NaOH?
1 mole 5.69 g = 0.142 mol NaOH 40.00 g s need to change grams to moles
q for NaOH
q 1mole Na = 22.99g 1 mol O = 16.00 g
1 mole of H = 1.01 g
q 1 mole NaOH = 40.00 g
q Gases and the Mole
Gases s Many
Many Gases
Gases of the chemicals we deal with
are gases.
are
s They are difficult to weigh, so we’ll
They
measure volume
measure
s Need to know how many moles of gas
Need
we have.
we
s Two things affect the volume of a gas
s Temperature and pressure
s Compare at the same temp. and
Compare
pressure.
pressure. Standard Temperature and
Pressure
Pressure
s Avogadro's Hypothesis  at the same
temperature and pressure equal
volumes of gas have the same number
of particles.
of
s 0ºC and 1 atmosphere pressure
0ºC
s Abbreviated atm
s 273 K and 101.3 kPa
s kPa is kiloPascal At Standard Temperature and
At
and
Pressure
s abbreviated STP
s At STP 1 mole of gas occupies 22.4 L
s Called the molar volume
Called
molar
s Used for conversion factors
s Moles to Liter and L to mol Examples
Examples
sWhat
What is the volume of 4.59
mole of CO2 gas at STP?
mole Density of a gas
Density
D = m /V
/V
s for a gas the units will be g / L
s We can determine the density of any
We
gas at STP if we know its formula.
gas
s To find the density we need the mass
To
and the volume.
and
s If you assume you have 1 mole than
If
the mass is the molar mass (PT)
the
s At STP the volume is 22.4 L.
s Examples
Examples
s Find the density of CO2 at STP.
at Quizdom
s Find the density of CH4 at STP. The other way
The
s Given
Given the density, we can find the
molar mass of the gas.
molar
s Again, pretend you have a mole at
Again,
STP, so V = 22.4 L.
STP,
sm = D x V
s m is the mass of 1 mole, since you
is
have 22.4 L of the stuff.
have
s What is the molar mass of a gas with a
What
density of 1.964 g/L?
density All the things we can change
All Volume 22.4 L PT Mass Moles
6.02 x 10 23 Representative
Particles
Atoms
Count Ions Percent Composition
Percent
Like all percents
s Part x 100 %
Part
whole
whole
s Find the mass of each component,
s divide by the total mass.
s Example
Example
s Calculate the percent composition of
Calculate
a compound that is 29.0 g of Ag with
4.30 g of S.
4.30 Getting it from the formula
Getting
If we know the formula, assume you
If
have 1 mole.
have
s Then you know the pieces and the
Then
whole.
whole.
s Examples
Examples
s Calculate the percent composition of
Calculate
C2H4? Examples
Examples
s What is the percent composition of
What
Aluminum carbonate.
Aluminum Percent to Mass
Percent
Multiply % by the total mass to find
Multiply
the mass of that component.
the
s How much aluminum in 450 g of
How
aluminum carbonate?
s Empirical Formula
Empirical
From percentage to formula The Empirical Formula
The
s The
The lowest whole number ratio of
elements in a compound.
elements
s The molecular formula the actual
The
ratio of elements in a compound.
ratio
s The two can be the same.
The
s CH empirical formula
2
sC H
24 molecular formula sC H
36 molecular formula s H2O both Finding Empirical Formulas
Finding
s Just find the lowest whole number ratio sC H O
6 12 6
s CH N
42
s It
It is not just the ratio of atoms, it is also
the ratio of moles of atoms.
the Calculating Empirical Formulas
Calculating
s Means
Means we can get ratio from percent
composition.
composition.
s Assume you have a 100 g.
s The percentages become grams.
s Turn grams to moles.
Turn
s Find lowest whole number ratio by
Find
dividing everything by the smallest
moles.
moles. s Calculate
Calculate Example
Example the empirical formula of a
compound composed of 38.67 % C,
16.22 % H, and 45.11 %N.
16.22
s Assume 100 g so
s 38.67 g C x 1mol C
= 3.220 mole C
38.67
12.01 gC
s 16.22 g H x 1mol H
= 16.1 mole H
16.22
1.01 gH
1.01
s 45.11 g N x 1mol N = 3.220 mole N
45.11
14.01 gN
14.01 Example
Example
s The ratio is 3.220 mol C = 1 mol C
3.220 molN
1 mol N
s The ratio is 16.1 mol H = 5 mol H
3.220 molN
1 mol N
sC H N
151
s Caffeine
Caffeine is 49.48% C, 5.15% H,
28.87% N and 16.49% O. What is its
empirical formula?
empirical Empirical to molecular
Empirical
s Caffeine
Caffeine is 49.48% C, 5.15% H, 28.87% N
and 16.49% O. What is its empirical
formula?
formula?
s Since the empirical formula is the lowest
Since
ratio the actual molecule would weigh the
same or more.
same
s By a whole number multiple.
s Divide the actual molar mass by the the
Divide
mass of one mole of the empirical formula.
mass
s You will get a whole number.
s Multiply the empirical formula by this. Example
Example
s A compound has an empirical
formula of ClCH2 and a molar mass
of 98.96 g/mol. What is its molecular
formula? s A compound has an empirical
formula of CH2O and a molar mass of
180.0 g/mol. What is its molecular
formula? Percent to molecular
Percent
s Take the percent x the molar mass
–This gives you mass in one mole of
This
the compound
the
s Change this to moles
–You will get whole numbers
–These are the subscripts
s Caffeine is 49.48% C, 5.15% H, 28.87% N
Caffeine
and 16.49% O. It has a molar mass of
194 g. What is its molecular formula?
194 Example
Example
s Ibuprofen is 75.69 % C, 8.80 % H, 15.51
% O, and has a molar mass of about
207 g/mol. What is its molecular
formula? ...
View
Full
Document
 Fall '11
 Edwards
 Mole

Click to edit the document details