MOLES!!!
Jan 02, 2016
MOLES!!!
Atomic mass Review
the mass of an atom expressed in atomic mass units
is an average of the isotopes for that element
listed on the periodic table
What is a mole?
A mole is a counting number (like a dozen or a gross)
the number of atoms in exactly 12 g of carbon-12
Molar mass
the mass in grams of one mole of a substance (g/mol)
same number as the atomic mass but the units are different
Example
The average atomic mass of an Fe atom is 55.85 amu.
The molar mass of Fe is 55.85 g/mol
Conversions
To convert between moles and mass:
mass = # of moles x ___g/1 mol
use molar mass
Directions
Add the examples to your 3.4 notes
Copy the problems and solve the problems.
Example #1
Find the mass of 3.000 moles of Fe.
Answer #1
3.000molFe x55.85g Fe = 167.6g Fe1 mole Fe
Example #2
Find the mass of 2.25 moles of Helium.
Answer #2
2.25 mol He x 4.00g He = 9.00 g He
1 mol He
Conversion #2
Converting from mass to moles.Mass (g) x 1 mole = # moles
molar mass (g)
Example #3
How many moles of carbon in 49.5 g of carbon?
Answer #3
49.5 g C x 1 mol C = 4.12 mol C
12.01 g C
Avogadro’s number
the number of atoms/particles in one mole of a substance
= 6.022 x 1023 atoms/particles
1 mole of anything is 6.022 x 1023 of that object
Conversion #3
Determine the number of atoms from # moles
# moles x 6.022 x 1023atoms = #atoms1 mole
Example #4
Determine the number of atoms in 4.00 moles of carbon.
The substance doesn’t matter if it is in moles.
Answer #4
2.41 x 1024 C atoms
4.00 mole C x 6.022 x 1023 C atoms1 mole C
Conversion #4
To convert number of atoms to moles9.05 x 1025 Fe atoms x 1 mol Fe
6.022 x 1023 Fe atoms = 150. moles of Fe
Example #5
Calculate the number of moles in 3.20 x 1023 atoms of iron.
The identity of the substances is not important when converting between moles & # of atoms.
Answer #5
0.531 moles of Fe
3.20 x 1023Fe atoms x 1 mole Fe
6.022 x 1023Fe atoms
Practice
Add to your notes:
Practice 1-4 p. 102 & practice 1-3 p. 103
Copy problem; Show work; Include units in work & answer.
0.850g H x 1 mol H = 0.842 molH
1.01g H
Practice Problem Answers
P. 102:
1. 238 g U 2. 1.2g U
3. 0.842 mol H, 0.859g H
4. 486.0 g Pb,
0.01132 mol Pb
p. 103
1. 4.2 x 1023 atoms Fe
2. 0.4796 mol Ag
3. 0.58 mol Os
Homework
p. 104: 4,5,6-10,12,13