Transcript Chemical Composition … Moles

Chemical Composition …
Moles
Chemistry
Mr. Lentz
Standards Addressed
3.1.10 D Apply scale as a way of relating
concepts and ideas to one another by
some measure.
3.4.10 A Explain concepts about the
structure and properties of matter.
Unit Topics
1. Atomic mass
2. Mole definitions
3. Percent composition
4. Empirical formulas
5. Molecular formulas
Some Definitions
Atomic particles:
Atomic number:
Mass number:
Isotopes:
Atomic mass:
– Mass spectrometer …
Atomic Mass
May be better described as an average
atomic mass …
Carbon has two common isotopes …
C-12 … 99.89% (.9989)(12) = 11.8668
C-13 … 1.11% (.0111)(13) = 0.1443
12.011
Atomic Mass
Actual masses of elements …
– Hydrogen = 1.66 X 10-24 g
– Carbon = 1.99 X 10-23 g
– Oxygen = 2.66 X 10-23 g
Atomic Mass Scale (amu)
– Hydrogen = 1.0 amu
– Carbon = 12.0 amu
– Oxygen = 16.0 amu
Problem
There is no easy way to measure the
mass of one atom
Solution …
– Change amu to grams
– Determine how many atoms are in 12.011 g
of Carbon
– Give this number a name
Avogadro’s Number
Is the number of atoms in 12.011 g of
carbon
Is equal to 6.02 X 1023
OR
602,000,000,000,000,000,000,000.
The Mole
Scientists gave Avogadro’s number of
things a name …
a
MOLE
One Mole
1 mole of marbles would cover the earth
50 miles deep
1 mole of grains of sand would cover the
US 1 cm deep
Could you count to Avogadro’s number?
Moles Defined
1 mole = 6.022 X 1023 “things”
1 mole = mass in grams (usually called
molar mass)
Molar Mass
Units … grams / mole
For elements … it is the atomic mass in
grams
For compounds … it is the sum of the
masses of the elements present
Molar Mass
What is the molar mass of copper?
answer = 63.6 g
What is the molar mass of water?
H2O H (2)(1.0) = 2.0
O (1)(16.0) = 16.0
18.0 g/mole