Transcript 6.02 x 10 23

Chapter 11
Mole
• SI base unit for measuring the amount of
substance
• The number of representative particles in
exactly 12 grams of pure carbon-12
• 1 mole = 6.02 x 1023 representative particles
Avogadro’s Number
• 6.02 x 1023 is called Avogadro’s number
• It is the number of representative particles
equal to 1 mole
• A representative particle is any kind of particle
and depends on the substance
– Water = molecule
– Copper = atom
– NaCl (salt) = formula unit
Molar/Formula Mass
• Molar/Formula mass is the mass in grams of 1
mole of any pure substance.
– units are g/mol
• Molar mass is equal to the atomic mass on the
periodic table
• Gram atomic mass: (found on periodic table)
– Ex: C = 12.011 amu
• This means 1 mole of Carbon = 12.011 g
• Let’s practice: Find the # of grams 1 mole of
the following is equal to
– Al
–H
–O
–P
Formula Mass/Molar Mass
• Formula or Molar mass is the mass of 1 mole
of a pure substance
H2O – covalent compound (metal/nonmental)
H
=
O
=
total =
2
1
moles
x
x
x
1g
16 g
=2g
= 16 g
avg. atomic mass= 18 g
• Let’s practice: Find the # of grams 1 mole of
the following is equal to
– H2O2
– NaCl
– Ca(NO3)2
– (NH4)3PO4
– N2O4
Percent Composition
• You can calculate the percentage of a certain
element in a compound
• Use the % Formula:
(Part/Whole) x 100 =
• 1st- we need the formula mass or the whole
• 2nd – we need the part found in the compound
• 3rd – divide and multiple by 100
• Example: What is the % of Hydrogen in H2O?
1st: Gram atomic Mass
– H2O – covalent compound (metal/nonmental)
H
=
O
=
total =
2
1
moles
x
x
x
1
16
=2
= 16
avg. atomic mass= 18 g
2nd: Hydrogen has a mass of 2g
3rd: %H = (2g/18g) x 100 = 11.11%
• What is the percent of oxygen in in H2O?
• The percent of each element in a compound
should add and equal 100.
• Lets practice: Find the percent composition of
each of the elements in the following
compounds.
– Fe2O3
– Cu2S
Molar Mass can be used as a Conversion
Factor
• What is the mass in grams of 2.5 mol of NaCl?
• Steps
– 1st : get the formula/molar mass of the compound
– 2nd: convert
Na = 1 x 23 = 23
Cl = 1 x 35.5 = 35.5
= 58.5g
?g = 2.5 mol NaCl
58.5 g NaCl =
1 mol NaCl
146 g NaCl
Avogadro’s number as a
conversion factor
• 1 mole = 6.02 x 1023 representative particles
• Representative particles can be atoms, molecules,
particles, formula units, pieces, etc
• How many molecules are in 3.5 moles of CO2?
?molecules = 3.5 mol CO2
2.1 x 1024 molecules CO2
6.02 x 1023 molecules =
1 mol NaCl
Volume Conversions
• At STP 1 mol = 22.4 liters of a gas
• What volume will 54.6 grams of CO2 occupy at
STP?
?liters = 54.6 g CO2
27.8 liters of CO2
1 mol CO2
44 g CO2
22.4 liters CO2
1 mole CO2
=
• Let’s practice:
1.How many grams are in 0.817 moles of
C2H2O6?
2.How many moles are in 60 grams of CaC03?
3.How many formula units of CaCl2 are in 45
grams?
Empirical Formulas
• The simplest whole number formula/ratio of a
compound. This means the equation cannot
be reduced anymore.
• Smallest whole number ratio
• Example: An unknown sample contains 25% H
and 75% C. What is the empirical formula
• Steps:
1st Convert % to grams 25 % = 25 grams H
(Assume you have 75 % = 75 grams C
100 grams total)
2nd Convert grams to 25 % = 25 g H x (1mol H/1g H)
moles by using the
= 25 mol H
atomic mass
75 % = 75 g C x (1mol C/12 g C)
= 6.25 mol O
3rd Divide by the smallest H = 25 mol/ 6.25 mol
# of moles to get the
=4
ratio
C = 6.25 mol / 6.25 mol
=1
4th Put numbers as
subscripts of elements CH
4
in formula
5th if a whole number is
not found after
dividing, multiply by a
factor to make it a
whole # (must multiply
all numbers by the
same factor)
Molecular Formula
• Indicates the actual amount of atoms present
• Must have molecular weight to determine
molecular formula
Steps:
1.Determine the empirical formula
2.Determine the empirical weight (molar mass
of the empirical formula)
3.Divide the molecular weight given by the
empirical weight you calculated
– If one, then the empirical formula is the same as
the molecular formula
4. If the answers from step 3 is a whole number,
then take the answer and multiply all
coefficients in the equation by the number.
5. If it is not a whole number you must multiple
by a factor to make it a whole number then
multiply each of the subscripts by it.
This will give the molecular formula.
Molecular Formula Example
• What is the molecular formula of a compound with
a molecular mass of 64 g/mol and an empirical
formula of CH4?
•
•
•
•
•
CH4
empirical mass = (12) + (4 x 1) = 16g/mol
Molecular mass = 64 g/mol
64 / 16 = 4
Multiply subscripts by 4
New formula is C4H16
Hydrates
• A compound that contains a certain amount
of water molecules
• Example:
CuSO4 . 5H2O
• Copper sulfate pentahydrate
• Hydrates can be dehydrated by heating
• The dehydrated form can be used to absorb
moisture from the air – like those packets you
find in your shoe boxes – deliquescent