NOTES: 10.1-10.2 – Chemical Quantities (The Mole / Molar Mass)
All Roads Lead to the Mole
What is a mole?
● A unit of measure used to count
,
● A number:
(Avogadro’s number)
● 1 mol =
(conversion factor)
, or
Count Amedeo Avogadro
● 1776-1856
• Lawyer who became interested in math and physics
• Discovered that equal volumes of different gases
• 9 years after his death, Joseph Loschmidt determined a constant and named it after Avogadro.
.
.
AVOGADRO’S CONSTANT =
1 mole =
1 mole =
1 mole (of a gas at STP) =
Why such a BIG number?
● because atoms, ions, molecules…are SO small!
● 5 Pound Bag of Sugar contains
● 1 Liter bottle of Water contains
Types of representative particles:
●
(breaks down into atoms)
●
●
(breaks down into ions)
●
Naming Representative Particles (R.P.s):
Examples: Name the representative particle for each substance given. For each molecule, state how many atoms
are present. For each formula unit, state how many ions make up the ionic compound.
H+ :
Cl2:
C2H6:
Cu(NO3)2:
Al:
NaCl:
R.P. Example #1:
How many moles are represented by 1.4 x 1022 molecules of H2O?
R.P. Example #2:
How many molecules of CO2 are present in 2.6 mol CO2?
R.P. Example #3:
How many individual atoms are in 5.2 mol CO2?
Avogadro’s Number Practice Problems:
1) How many moles of magnesium are represented by 1.25 x 1023 atoms of magnesium?
ANSWER:
2) How many C3H8 molecules are in 2.12 mol of propane (C3H8)?
ANSWER:
How about MOLES and MASS?
● when we measure out substances in the lab, it is not practical to count individual molecules…
● instead, we can use a balance to weigh out a certain amount…
● it is therefore useful to have a way to convert from moles to mass (and vice versa!)
MOLAR MASS … a.k.a. Molecular Weight (MW)
• Molar mass =
• Molar mass can be determined by adding up the atomic masses from the periodic table.
Molar Mass Example #1: Find the molar mass of CH4.
Molar Mass Example #2: Find the molar mass of Mg(OH)2
Molar Mass Example #3: Find the molar mass of MgSO4•7H2O.
Molar Mass Practice Problems:
● Determine the molar mass of the following compounds:
1) H2O2
2) Carbon tetrabromide
3) (NH4)2CO3
4) Aluminum sulfate
5) Ca(NO3)2
Molar Mass Example #1: How many grams are in 7.20 moles of dinitrogen trioxide?
Molar Mass Example #2: Find the number of moles in 92.2 g of iron(III) oxide.
Gram ↔ Mole Conversion Practice Problems:
1) How many grams are in 9.45 mol of diphosphorus pentachloride?
2) Find the number of moles in 107.5 g of iron(II) chlorate.
3) Find the number of grams in 3.32 mole of KNO3.