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Transcript
Introduction to Quantities in Chemical
Formulas
4.1: Proportions in
Compounds
Compare carbon dioxide and carbon
monoxide
Carbon dioxide:
Chemical formula :
Physical Properties:
When does it form: when there is a large amount of O2
available
Affect to humans: plants use it to produce O2, which we
breathe
Oxygen Ratio:
Carbon monoxide:
Chemical formula :
Physical Properties:
When does it form: when there is a small amount of O2
available
Affect to humans: -binds to hemoglobin,
-not able to transport oxygen to the body
-tissue damage and organ failure
C
o
-O
-C
1:
ato
C
-C
-O
Oxygen Ratio:
1:
at
Law of Definite Proportions: the proportions of
elements
in a specific compound, are always the same,
no matter how the compound is made.
-The properties of a substance will depend on:
1) the elements in the compound
2) the quantity of each element in the compound
Ex. 2 : O2 vs. O3
So to analyze chemical reactions quantitatively….
Stoichiometry: the study of the relationships between the quantities of
reactants and products involved in chemical reactions
Law of Definite Proportions
Ex. 1 : Sort the following atoms and
determine the compound's chemical formula.
H
H
O
H
O
O
OH
H
O
O
H
H
H
H
H
O
H
O
H
H
H
O
H
H
H
H
O
H
H
O
H
H
H
Hydrogen Box
Oxygen Box
# of oxygens =
ratio:
O
H
# of hydrogens =
:
The compound's chemical formula is: _______________
Use the law of definitive proportions to
determine the unknown masses.
hydrogen + chlorine
?
Exp 1
2g
+ 71 g
73 g
6g
+ 213 g
219 g
?g
+ 17.75 g
18.25 g
Exp 2
Exp 3
Exp 4
150 g + ? g
?g
4.2 Relative Atomic Mass
-Relative atomic mass helps us to understand how the mass
numbers on the periodic table were found
-When John Dalton came up with the Billiard Ball model,
he also determined a way to express the mass of atoms
-What was the billiard ball model and what did it tell us
about the mass of atoms?
-Using this information and the law of definite proportions,
Dalton was able to express the masses of atoms
RELATIVE TO EACH OTHER!
-For example, if we obtain the following results from
the reaction of calcium and oxygen to form calcium
oxide:
calcium + oxygen
40g
16g
calcium oxide
56g
-Now, Dalton used hydrogen first because it was the
lightest element and gave it a mass of 1.
-he compared all the other element to this value
For ex. : when Dalton looked at water, he saw thta 1 g of
hydrogen combined with 8 g oxygen
-so he gave oxygen a mass of 8
-this was a mistake since 2 atoms of oxygen combines with
one atom of hydrogen
-So oxygen must have a relative atomic mass of 16
So what do we mean by relative atomic mass
Relative atomic mass: mass of an element that
would react with a fixed mass of a standard
element
-we are currently using carbon -12 as our standard
element
Why?
Units, Units, Units!
-Remember IUPAC and SI units, the proper units for
the mass of an atom are atomic mass units or "u"
Atomic mass unit: 1 u is equal to 1/12th the mass of a
carbon-12 atom
and just to put this into perspective:
1 u = 1.66´ 10-27 kg (thats really tiny!)
Ex.1 - What is the mass of 1 carbon-12 atom? Use
atomic mass units.
Ex.2 - If a titanium atoms weighs 4 times a carbon-12 atom,
calculate the atomic mass of titanium in u.
Bonus: Express this in kg
Homework
Pg.162 #1
Pg.164 # 1,3,4