Download CH 10 - sierackichem

Counting by weighing
• Calculate the amount of pennies in the cup by
weighing them. You may take 10 pennies out
of the cup to weigh them, but do not count
what is in the cup
• Atoms are too small to count so we weigh an
amount (mole) and calculate the number
Some words mean numbers
• Pair
• Dozen
• Baker’s dozen
• Gross
• Ream
Mole
1 mole = 6.02 x 1023 representative particles
( the number of carbon-12 atoms in 12.00 g
obtained by counting by weighing)
Atom, Molecule and Ions
• Representative particles – smallest
particle of that substance
Substance Representative Particle
element
molecular compound
(covalent bond)
ionic compound
atom
molecule
formula unit
Practice:
1. Determine the number of FU in
.866 moles of AgNO3?
2. Find the molecules in
0.98 moles of Cl2
3. Determine the moles in 7.83 x 1017
atoms of Fe
Molar Mass
(counting by weighing mass)
Mass of 1 mole of a substance
Element
atomic mass in g
Compound
add up all the atomic masses for
the atoms in the substance
all
Calculate the Molar mass
• Ca
• H2
• KNO3
• (NH4)2S
Remember
1 mole = 6.02 x 1023 r.p.
1 mole = molar mass(g)
Try these:
• Calculate the
• Calculate the
Fe(OH)3
• Calculate the
• Calculate the
of CO
moles of 1.2 g H2
moles of 5.6 x 1025 f.u.
grams of 6.7 moles SO3
molecules of 4.0 moles
Molar Volume
The volume of 1mole of a gas at
standartd temperature – 0oC
standard pressure – 1 atmosphere
(pressure at sea level)
1 mole gas at STP = 22.4 L
Remember
1 mole = 6.02 x 1023 r.p.
1 mole = molar mass(g)
1 mole = 22.4 L gas
Multistep problems
• How many atoms on 47.8L of Ar?
• How many fu in 18.9 g NaCl?
• How many g in 4.5 x 1013 atoms K?
Percent Composition
% element = g element x 100%
g total
Formulas
• Empirical
simplest whole number ratio
• Molecular Formula
actaul number of atoms in the
formula
Empirical formula
Get moles
• Use moles as subscripts
• Divide by common factor
(usually smallest number)
• Get whole number
Practice:
A compound has
13.5 g Ca
10.8 g O
.675 g H
What is its empirical formula?
Molecular formula
Set up table:
Empirical
Molecular
Molar Mass
formula
Reactions of an Iron Nail
• Do steps 1,2,3,4,5
• Return to class
• Do steps6,7,8,9,10,11
Chemical Measurements
• Atomic Mass
The weighted average of all the mass
numbers for all the isotopes of the atom
(a.m.u.)
• Formula Mass
The sum of all the atomic masses for all
atoms in the compound. (a.m.u.)
Calculate the atomic mass or formula
masses
• Na
22.99 amu
• Cl
35.45
amu
• Br2
159.80 amu
• NaCl
58.45 amu
• H2O
• Mg(OH)2
18.02 amu
58.33 amu
Molar mass element
The mass of 1 mole = atomic mass (g)
What is the mass of 1 mole of
He?
Pb?
Cl?
Molar Mass
=
=
=
The mass of 1 mole
( 6.02 x 1023) of
representative particles
The atomic mass in g
The formula mass in g