Introduction to Quantities in Chemical Formulas4.1: Proportions in CompoundsCompare carbon dioxide and carbon monoxide

Carbon dioxide: Chemical formula :

Physical Properties:

When does it form: when there is a large amount of O2 availableAffect to humans: plants use it to produce O2, which we breatheOxygen Ratio:

Chemical formula :

Physical Properties:

When does it form: when there is a small amount of O2 availableAffect to humans: -binds to hemoglobin, -not able to transport oxygen to the body -tissue damage and organ failure

Oxygen Ratio:

Carbon monoxide:

CO2

-Colourless-Odourless

1: 2 (1 carbon atom for every 2 oxygen atoms)

1: 1 (1 carbon atom for every 1 oxygen atom)

CO

-Colourless-Odourless

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: 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 compound2) the quantity of each element in the compound

Ex. 2 : O2 vs. O3

Law of Definite Proportions

Ex. 1 : Sort the following atoms and determine the compound's chemical formula.

OO O

H

HH

H

H H

HH

HHH

HH

H

H

H

H H

HH

HH

HO O O

O O OO

H

OO

Oxygen Box Hydrogen Box

# of oxygens =

# of hydrogens = ratio: :

The compound's chemical formula is: _______________

Use the law of definitive proportions to determine the unknown masses.

Exp 1 2 g + 71 g 73 g

Exp 2 6 g + 213 g 219 g

Exp 3 ? g + 17.75 g 18.25 g

Exp 4 150 g +

? g ? g

hydrogen + chlorine

?

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 calcium oxide 40g 16g

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 #1Pg.164 # 1,3,4