unit v: the mole concept v.2. the mole. the mole concept 1 mole = 602 000 000 000 000 000 000 000 a...
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The Mole Concept
1 mole = 602 000 000 000 000 000 000 000
A really BIG number
1 mole = 6.02 x 1023 molecules = Avagadro’s Number
Avagadro’s Number
It was long after Avogadro that the idea of a mole was introduced.
Since a molecular weight in grams (mole) of any substance contains the same number of molecules, then according to Avogadro's Principle, the molar volumes of all gases should be the same.
The number of molecules in one mole is now called Avogadro's number.
How big is Avogadro’s number? An Avogadro's number of standard soft drink
cans would cover the surface of the earth to a depth of over 200 miles
How big is Avogadro’s number? One mole of Kit-Kat bars (~1cm thick) piled
high would reach 6.02X 1018 km Pile of Kit-Kat bars is 1 billion times
the radius of the solar system
6 x 109 km
How big is Avogadro’s number? If Aliens came to Earth to distribute $1 mole
(Canadian) Each Canadian would get
149
23
101$106
106$
people
Mole Redefined
Strictly speaking a mole is the number of carbon atoms in exactly 12 g of carbon having a mass of 12 [C-12 isotopes]
Atomic Mass
The mass of 1 mole of atoms of an element Remember: 1 mole: 6.02 x 1023
Eg. The mass of 1 mole of “C” atoms is 12.0 g The mass of 1 mole of “Ca” atoms is 40.1g
Molar Mass (Molecular Mass) The mass in grams of 1 mole of molecules
of an element or compound
In most cases the molar mass of an element is the mass shown on the periodic table expressed in grams
Be careful here !!!!
Diatomic Elements: Molar Mass Molar Mass of our
diatomic elements will be different from their Atomic Masses
H2(g) O2(g) N2(g) F2(g) Cl2(g) Br2(l) I2(s)
Special Elements: Molar Mass Sometime Phosphorus is P And Sometimes it is P4
Sometimes sulphur is S And sometimes it is S8
Assume all the other elements are monatomic
Atomic Mass vs. Molar Mass
Element Symbol Formula Atomic
Mass
Molar
Mass
Neon Ne
Bromine Br
Silicon Si
Hydrogen H
Iodine I
Iron Fe
Atomic Mass vs. Molar Mass
Element Symbol Formula Atomic
Mass
Molar
Mass
Neon Ne Ne 20.2 20.2
Bromine Br Br2 79.9 159.8
Silicon Si Si 28.1 28.1
Hydrogen H H2 1.0 2.0
Iodine I I2 126.9 253.8
Iron Fe Fe 55.8 55.8
Finding the Molar Mass of Compounds Finding the molar mass of a compound
involves: using the periodic table to look up the mass of
every atom involved Adding up the masses of the atoms and
expressing the resulting mass in g/mol
Calculating Molar Mass of a Compound
H20
2(1.0) + 1(16.0) = 18.0 g/mol
Note: the units for molar mass = g/molAll atomic masses on the periodic table are
expressed to one decimal placeTherefore, your answers should be expressed
to one decimal place as well
Finding the Molar Mass of Compounds
Ca(NO3)2
1 Ca: 40.1 g/mol
2 N: 2(14.0 g/mol)
6 O: 6(16.0) g/mol
164.1 g/mol
Finding the Molar Mass of Compounds
ammonium phosphate
(NH4)3PO4
3 N: 3(14.0 g/mol)
12 H: 12(1.0 g/mol)
1 P: 1(31.0 g/mol)
4 O: 4(16.0 g/mol)
149.0 g/mol
Hydrated Compounds
Treat water like an element with a molar mass of 18.0g/mol
H20
2(1.0) + 1(16.0) = 18.0 g/mol
Find the molar mass of cobalt (II) chloride hexahydrate? CoCl2 ●6H20
58.9 + 2(35.5) + 6(18.0) = 237.9 g/mol
Grams Moles Conversion Units
MM = molar mass g = grams mol = mole
Conversion Factors
MM g
1 mol
1 mol
MM gOR
Example 1b: grams moles
How many moles are present in 6.34 x 10-5 g of K2SO4?
3.64x 10-7 mol of K2SO4
Example 1c: grams moles
Find the number of moles in a 391 g sample of nitrogen dioxide (NO2)
8.50 mol of NO2
Example 3a: mg moles
62.6 mg of C12H22O11 = ? moles Plan: mg g mol
0.000183 mol or 1.83x10-4 mol of C12H22O11
Finding the molar mass given mass and moles Trick to these questions is that there is no
formula given – it is an unknown compound containing
MM = mm (g)
moles
Example
For a compound of phosphorus and chlorine, it is found that 0.200 moles of the gas has a mass of 27.5 g
Find the molar mass of the gas
137.5 g/mol
Gases and Moles
The volume occupied by a certain amount of gas depends on the temperature and the pressure
Standard Temperature and Pressure (STP) Standard temperature 0◦C (273 K) Standard Pressure 101.3 kPa (1 atm)
Gases and Moles
The Molar Volume @ STP is
22.4 L
1 mol
1 mol
22.4 LOR
ONLY FOR GASES ONLY FOR GASES AT STPAT STP
Example 1a: Moles Litres Conversion Find the volume (L) occupied by 0.060 moles
of CO2 at STP
1.344 L
Example 1c: Moles Litres Conversion 3.96 x 10-5 mol N2O4 (g) = ? L at STP
8.87 x 10-4 L or 0.000887 L
Example 2b: Litres to Moles Conversion Find the number of moles in a 264.0 ml
sample of NO2 at 0◦C and 101.3 kPa.
0.0118 mol
Atoms and Molecules
(NH4)2CO3
2 “N” Atoms
1 molecule
8 “H” Atoms
1 molecule
1 “C” Atoms
1 molecule
3 “O” Atoms
1 molecule
14 Atoms
1 molecule
Example 1a. Moles molecules How many molecules are there in a 0.25 mol
sample of CO2?
1.505 X 1023 molecules
Molely Practice
Find the number of “H” atoms in 4.0 moles of ammonia (NH3).
Plan: moles molecules atoms
7.224 x 1024 “H” atoms