molar mass, and other simple math!

1st of all, what is a molar mass? it is the sum of the masses of the atoms.We did this when we did molar mass, but not much.

for instance - what is the molar mass of CO2 ?you take the mass of the carbon- 12.011 and add the mass of 2 oxygens- 15.99 x 2

then add them up! 12.011 + 31.98=43.99 grams!

not too bad! try finding the molar mass of water!

great!

now, what if you had 5 moles of water, how much would that weigh?take the moles (5) x the mass of water ( 18.0158g/mole) and get a total mass of 90.079 grams

44.009

75.971C

HU?

O = 15.999 g/ mole

=12.011 g/ mol

=14.077 g/mol

OO O

How much do these compounds weigh?

C O

76.011C OOif these atoms have these weights...

great, now lets try percent composition. it is the part BY MASSthat each element is in a compound.All percents are just part over total. so there you go, find the part, find the total.

for instance, if I had a compound that had 33 grams of nitrogen and 45 grams of oxygen what is the percent composition of each?

1st find the total grams. 33 + 45= 78 grams.now divide eachthere is another way to do this, and that is from the formula itselfsay you knew you had some diphosphours decaoxide, and you wanted to know how much oxygen you had.

1st- P2O10 has a total mass of ...( yes molar mass of this) , P=30.974 x 2= 61.948and oxygen is 15.99 x 10 = 159.9 g total is 221.848 grams and oxygen % is 159.9/221.848=.72 so 72% oxygen by mass

OO O

= 15.999 g/ mole

=14.077 g/mol

what is the % nitrogen in this compound

if these atoms have these weights...

more math?

O

= 75.971

OO O

O = 15.999 g/ mole

=14.077 g/mol

=28.001

1st find the parts and the whole

O = 15.999 g/ mole

=14.077 g/mol

so the part that is Nitrogen is

=28.001

75.971OO O

this means "out of" it also means divided by

.3685, or 36.9 %

now lets try emperical formula- also called simplest formula it is the smallest ratio of the elements.

if you are given a formula, it may or may not be the simplest

CO2

S4O8 SO2H2OHNO3

C6H12O6 CH2O

How to do it:1st you are given grams amounts, or %s. either way, turn them into moles ( divide by molar mass)

2nd, looking at the answer from 1, divide all by smallest, this gives you whole numbers!

·Product-a substance that is produced by a chemical reaction.

Ca Br

Br

Ca

Br

Br

·Reactants- Substance that enters a chemical reaction.

Chemical Reactions

Chemical Reactions ·Reactants- Substance that enters a chemical reaction.

Ca

Br

Br

Ca

Br

Br

·Product-a substance that is produced by a chemical reaction.

Chemical Equation

·

Word Eqn. Have words in them Formula Eqn. Have symbols of the element

<http://en.wikipedia.org/wiki/Chemical_reaction

·Formula Equation - Ca +O2 → CaO

·Word Equation - Calcium + Oxygen = Calcium Oxide

3 things that must be true of chemical reactions include-

1. they must represent known facts( you can’t make them up, the reaction actually

has to happen)how do you know?

2. Formula’s must be correct ( balance ionic compounds, write covalent

compound correctly)

3. Law of conservation of massBalance reaction! Use coefficients to make

sure reactant amounts and product amounts are equal

H2 + O2 H2O

Nitrogen gas and Sulfer create Dinitrogen tetrasulfide

Na2O + H2O = NaOH

Ca(OH)2 + Na = NaOH + Ca

Fe + H2O = Fe2O3 + H2

Na + O2 = Na2O

MgO + K = K2O + Mg

Fe + O2 = Fe2O3

Ca

Br

Cl HH

Fe

Mg

Types of reactionsall reactions can be grouped into 5 general types

1. synthesis - 2 or more reactants turn into ONE product

+ Cl Cl

O HH O+Mg O HO H

2. Decomposition- the reverse of synthesis, thistakes ONE REACTANT and makes 2 or more products

N

O

O

O

C

N

H

H

H

H

O O

N

HHN

C O O

OO

CO3 ⇒ C + O2

NO2 ⇒ N2 + O2

N

N

Br

Ca

C

C OO

Cl H

H

Cl

O O

N

Mg

Fe

single replacement reactions

H

Cl H

Mg

Cl

Fe

O O

N

N

O O

N

O

O

Na

H

O

O

HO

O

C

H H

H

H

HO

H

H H

H

H

C C

C OO

C

H O H

O O

O OO O

H O H

H

O

H