How do you measure how much?
You can measure mass, volume,
or you can count pieces of a substance. We measure mass in grams. We measure volume in liters.
We count pieces in MOLES. No, not that kind of mole!!!
Moles Defined as the number of carbon atoms in
exactly 12 grams of carbon-12. 1 mole is 6.02 x 1023 particles. Treat it like a very large dozen. 6.02 x 1023 is called Avogadro's number. The units of Avogadro’s number can be
whatever particle you are counting.– Examples: atoms, molecules, ions, formula units,
etc…– In chemistry these are called Representative
Particles
What are Representative Particles?
The smallest pieces of a substance. For an element it is an atom.
– Unless it is diatomic
For a covalent compound it is a molecule. For an ionic compound it is a formula unit. If it has a charge, it is an ion.
How do We Use Moles? Moles are used as conversion factors. This means they are used to change units. Remember, when solving using conversion
factors there are 3 questions you want to ask yourself:– What unit do you want to get rid of?– Where does it go to cancel out?– What can you change it into?
Calculation question 1 How many molecules of CO2 are the in 4.56
moles of CO2 ?
Answer: 2.75 x 1024 molecules of CO2
Calculation question How many moles of water is 5.87 x 1022
molecules of water?
ANSWER: 0.0975 moles of water
Measuring Moles The atomic mass unit (amu) is one twelfth the
mass of a carbon 12 atom. Since the mole is the number of atoms in 12
grams of carbon-12, the decimal number on the periodic table is:– The mass of the average atom in amu.
This mass is equivalent to the mass of 1 mole of those atoms in grams.
Gram Atomic Mass
The mass of 1 mole of an element in grams. 12.01 grams of carbon has the same number
of pieces as 1.008 grams of hydrogen and 55.85 grams of iron.
We can write this as: 12.01 g C = 1 mole
We can count things by weighing them.
Examples
How much would 2.34 moles of carbon weigh?
28.1 grams of C How many moles of magnesium in 4.61 g of
Mg?
0.190 moles of Mg
What about compounds?
In 1 mole of H2O molecules there are two moles of H atoms and 1 mole of O atoms.
To find the mass of one mole of a compound: – Determine the moles of the elements they have.– Find out how much their mass is by using the
periodic table and then add them up.
Example What is the mass of one mole of CH4?
1 mole of C = 12.01 g 4 mole of H x 1.01 g = 4.04g
1 mole CH4 = 12.01 + 4.04 = 16.05g
The Gram Molecular mass of CH4 is 16.05g
Gram Molecular Mass or GMM The mass of one mole of a molecular
compound.
Gram Formula Mass - The mass of one mole of an ionic compound.
Calculated the same way as GMM. What is the GFM of Fe2O3?
2 moles of Fe x 55.85 g = 111.70 g 3 moles of O x 16.00 g = 48.00 g The GFM = 111.70 g + 48.00 g = 159.70g
Molar Mass
The generic term for the mass of one mole. The same as gram molecular mass, gram
formula mass, and gram atomic mass. This is the term we will be using in class.
I do NOT weigh that much! The balance must be lying!!!
Examples Calculate the molar mass of the following
and tell me what type it is (gmm, gfm, or gam).
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
149.12 g/mol
180.18 g/mol
Molar Mass
The number of grams in 1 mole of atoms, formula units, or molecules.
We can make conversion factors from these. It will allow us to change grams of a
compound to moles of a compound. Or moles to grams.
For example
How many moles is 5.69 g of NaOH?
g
mole NaOH g 69.5
need to change grams to moles for NaOH
For example
How many moles is 5.69 g of NaOH?
g
mole NaOH g 69.5
need to change grams to moles for NaOH
1mole Na = 22.99g 1 mol O = 16.00 g 1 mole of H = 1.01 g
For example
How many moles is 5.69 g of NaOH?
g
mole NaOH g 69.5
need to change grams to moles for NaOH
1mole Na = 22.99g 1 mol O = 16.00 g 1 mole of H = 1.01 g add these together to get the molar mass – use it to convert!
1 mole NaOH = 40.00 g
For example
How many moles is 5.69 g of NaOH?
g 40.00
mole 1 NaOH g 69.5
need to change grams to moles for NaOH
1mole Na = 22.99g 1 mol O = 16.00 g 1 mole of H = 1.01 g
1 mole NaOH = 40.00 g
For example
How many moles is 5.69 g of NaOH?
NaOH mol 0.142 = 40.00
mole 1 NaOH g 69.5
g
need to change grams to moles for NaOH
1mole Na = 22.99g 1 mol O = 16.00 g 1 mole of H = 1.01 g
1 mole NaOH = 40.00 g
Examples
How many moles is 4.56 g of CO2 ?
How many grams is 9.87 moles of H2O?
0.104 mol CO2
177.86 g H2O
GasesMany of the chemicals we deal with are gases.They are difficult to weigh, so we’ll measure
volume.We still need to know how many moles of gas
we have.Two things affect the volume of a gas:
– Temperature and pressure.So we have to compare at the SAME temp. and
pressure.
Standard Temperature and Pressure
Avogadro's Hypothesis - at the same temperature and pressure equal volumes of gas have the same number of particles.
0ºC and 1 atm pressureabbreviated STPAt STP, 1 mole of gas occupies 22.4 LCalled the molar volume.
ExamplesWhat is the volume of 4.59 mole of CO2 gas
at STP?
How many moles is 5.67 L of O2 at STP?
What is the volume of 8.8g of CH4 gas at
STP?
We have learned how to:
change moles to gramsmoles to atomsmoles to formula unitsmoles to moleculesmoles to liters
Percent Composition
Like all percents: Part x 100 %
whole Find the mass of each component, divide by the total mass.
Example
Calculate the percent composition of a compound that is 29.0 g of Ag combined with 4.30 g of S.
Percent to Mass Multiply % by the total mass to find the mass
of that component. How much aluminum in 450 g of aluminum
carbonate?
The Empirical FormulaThe lowest whole number ratio of elements in
a compound.The molecular formula is the actual ratio of
elements in a compound.The two can be the same. CH2 empirical formulaC2H4 molecular formulaC3H6 molecular formulaH2O both
Finding Empirical FormulasJust find the lowest whole number ratio.
C6H12O6 , CH4N2
It is not just the ratio of atoms, it is also the ratio of moles of atoms.
Calculating Empirical FormulasWe can get ratio from percent composition.Assume you have 100 g.The percentages become grams.Convert grams to moles. Find lowest whole number ratio by dividing
everything by the smallest moles.
ExampleCalculate the empirical formula of a compound
composed of 38.67 % C, 16.22 % H, and 45.11 %N.
Assume 100 g so: = 3.22 mole C
= 16.1 mole H
= 3.22 mole N
1 mol C38.67 g C
12.01 g C
1 mol H16.22 g H
1.01 g H
1 mol N45.11 g N
14.01 g N
Example Continued:The smallest number of moles is 3.22 mol so
divide your answers by 3.22 to get the mole ratio for the formula.
The ratio is:
So the formula is: C1H5N1
3.22 mol C = 1 C
3.22 mol16.1 mol H
= 5 H3.22 mol
3.22 mol N = 1 N
3.22 mol N
Additional Examples: A compound is 73.9 % Hg and 26.1 % Cl.
What is the empirical formula?
Caffeine is 49.48% C, 5.15% H, 28.87% N and 16.49% O. What is its empirical formula?
HgCl2
C4H5N2O
Empirical to molecularSince the empirical formula is the lowest ratio the
actual molecule would weigh the same or more.
This difference in weight would be by a whole number multiple.
To find this multiple: divide the actual molar mass by the the mass of one mole of the empirical formula.
You will get a whole number.
Multiply the subscripts of the empirical formula by this number.
Example A compound has an empirical formula of
ClCH2 and a molar mass of 98.96 g/mol. What is its molecular formula?
A compound has an empirical formula of CH2O and a molar mass of 180.0 g/mol. What is its molecular formula?
Cl2C2H4
C6H12O6
Percent Composition to Molecular Formula: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?
C13H18O2
Example: Caffeine is 49.48% C, 5.15% H, 28.87% N
and 16.49% O. It has a molar mass of 194 g. What is its molecular formula? C 0.4948*194g = 95.99 g C = 8 mol C
H 0.0515*194g = 9.99 g H = 10 mol H
N 0.2887*194g = 56.01 g N = 4 mol N
O 0.1649*194g = 31.99 g O = 2 mol O
1 mol C95.99 g C
12.01 g C
1 mol H9.99 g H
1.01 g H
1 mol N56.01 g N
14.01 g N
1 mol O31.99 g O
16.00 g O
C8H10N4O2