Transcript molar mass

Chem 11: Finish Unit 4 start
Unit 5
5-3
Writing Formulas for Ionic
Compounds
1.
2.
3.
4.
tin (IV) sulphate
ammonium sulphate
iron (II) sulphate
Hg2+ and Cl- forms an ionic compound
Common Acids (p74)
Memorize the following:
acid
name
HCl
hydrochloric acid
H3PO4
phosphoric acid
HNO3
nitric acid
H2SO4
sulfuric acid
CH3COOH
acetic acid
Daily Question
Complete the table
Cation(C)
Anion(A)
or
Neutral (N)
Sr2+
OHNH4+
Ar
Monoatomic(M)
elements
Diatomic (D)
Triatomic (T)
or Polyatomic (P)
Charge
The
and
!
1) Words for Numbers
 a “pair” of shoes
 refers to 2 shoes
 a “dozen” cats
 refers to 12 cats
 a “mole” of particles
 refers to (insert large number) of molecules
1) Words for Numbers
 a mole is simply just a word representing a
large number
 1 mole = 6.022 x 1023
 this number is often referred to as
“Avogadro’s number”
a - voe - ga - dro
REMEMBER
 a mole is just a really really big number!
6.02 x 1023
1 mol = Avogadro’s Number
4 mol = 4 x Avogadro’s Number
0.5784 mol = 0.5784 x Avogadro’s Number
we abbreviate mole to mol
(similar to kilogram to kg)
0 mol = 0
2) It’s really big…
 imagine a pea
 it has a volume of about 0.20 cm3
 how many peas would it take….?
to fill a fridge
to fill a 3 story home
1000 homes
106
1m deep across BC
1018
1m deep on all land
1m deep on entire planet
109
1012
1021
≈ to a mole
this is a large number of particles…
REMEMBER
just like a 1
equals 12
1
equals 6.022
x 1023
3) Why?
 why bother with a new unit?
 what’s easier to say:
 3 moles atoms
 1.807 x 1024 atoms
that’s a pretty good reason
4) Molar Mass
 atoms and molecules have mass
 we measure numbers of particles using the
mole
 a mole of atoms will have a mass
 this mass is called the molar
mass
4) Molar Mass
 molar masses are quoted in units of g/mol
g
3.2g
3.2

mol
1mol
there are 3.2 grams
in every 1 mole of substance
4) Molar Mass
 here are some molar masses:
 one mole of……
 has a mass of…
–oxygen
16.00 g/mol
–carbon
12.01 g/mol
–helium
4.00 g/mol
4) Molar Mass
 molecular weight is equivalent to molar mass!
 the periodic table lists all of the molar masses
molar
masses
in
g/mol
REMEMBER
a

represents big number
is the number of grams (it’s
mass) in a mole of substance
Try It
 if a dozen eggs weighs 15 g, how much
does 4 dozen eggs weigh?
15 g
= 6.0 x 10 g
4 dozen 
dozen
 how much does 4.0 moles of carbon weigh?
12.0 g
4.0 mol 
mol
= 48 g
use this “cancellation” method to ensure you are doing it properly!
4) Molecular Mass
 molecular mass is found by summing the
HO
molar mass of each atom in a molecule
 for example - the molar mass of Ca(HCO3)2
2
# atoms x molar mass of atom
molecule’s molar mass
5) Calculations
 a common theme of Chem 11 will be finding
mass, moles or molar mass
 MEMORIZE (and understand) this:
mass
recall units of molar mass
MM 
moles
MM  moles  mass
if you are EVER
mass
moles 
MM
unsure all you need to do is
CHECK the UNITS
5) Calculations
 for ALL CALCULATIONS I want to see you
CANCELLING UNITS!
 example:
how many moles are in 36.0 g of H2O?
 MM = 18.0 g/mol
 mass = 36.0 g
moles 
mass
MM
mol
36.0g
 36.0g 
moles 
18.0g
18.0g / mol
= 2.00 mol
it is a few extra steps, but it is worth it
when the answer comes out right!
Remember
 a mole is just a large number of particles
 consider the following chemical reaction:
2 H2 (g) + O2 (g)  2 H2O (l)
 you can now describe this as:
 2 molecules of hydrogen react with a molecule of
oxygen to produce 2 molecules of water
or equally well as
 2 mol of hydrogen react with 1 mol of oxygen to
produce 2 mol of water
Try Its
find….
 mass of 0.034 mol of Li
0.034 mol 
6.94 g
 0.26g
mol
 # atoms in 4 mol of hydrogen
6.02x1023 atoms
4.0 mol 
 2.4x1024 atoms
mol
 mass of 0.314 mol of CO2
(12.0 + 2  16.0) g
0.034 mol 
 13.8g
mol
 # atoms in 4 g helium
find moles helium, then convert to atoms