### Percent Composition

Percent composition is the percentage by mass of a "species" in a chemical formula.  You are trying to find the percentage of how much one element is in a compound.  You can find this by using the molar mass of each compound.
**(sometimes the percentage may not add up to 100% because of the rounding.  If the percent is somewhere near 99.9% its ok.)**

Ex.1 What is the percentage composition of NaCl?
First we need the following:
Total Molar Mass of NaCl: 58.5g/mol
Molar Mass of Na: 23.0 g/mol
Molar Mass of Cl: 35.5 g/mol
Then we do the calculations like so:
% of Na = 23    g/mol   x  100% = 39.3%
58.5 g/mol

% of Cl = 35.5 g/mol   x   100% = 60.7%
58.5 g/mol
Total percentage: 100%

Ex.2 What is the percentage composition of ZnSO3?
Total Molar Mass of ZnSO3: 145.5 g/mol
Molar Mass of Zn: 65.4 g/mol
Molar Mass of S: 32.1 g/mol
Molar Mass of O: 16.0 x 3 = 48.0 g/mol

% of Zn = 65.4  g/mol  x  100% = 44.9 %
145.5 g/mol

% of S = 32.1   g/mol  x  100% = 22.1%
145.5 g/mol

% of O = 48.0    g/mol  x  100% = 33.0%
145.5 g/mol
Total percentage: 100.0%

Ex. 3 What is the percentage composition of Zn3(PO4)2?
Total Molar Mass of Zn3(PO4)2: 386.2 g/mol
Molar Mass of Zn3: 65.4 x 3 = 196.2 g/mol
Molar Mass of P: 31.0 x 2 = 62.0 g/mol
Molar Mass of O: 16.0 x 8 = 128.0 g/mol

% of Zn = 196.2 g/mol  x  100% = 50.8%
386.2 g/mol

% of P = 62.0    g/mol    x  100% = 16.1%
386.2 g/mol

% of O = 128.0 g/mol  x  100% = 33.1%
386.2 g/mol
Total percentage: 100%

Ex. 4 If a compound contains 54 grams of Al, 36 grams of C, 56 grams of N, some amount of O, and has a total molar mass of 226 grams, what is the percentage composition?
First, we need to find the molar mass of the amount of O.  To do this we do:
226 - 54 - 36 - 56 = 80  <--- this is the molar mass of O.

% of Al = 54.0   g/mol  x  100% = 23.9%
226.0 g/mol

% of C = 36.0   g/mol  x  100% = 15.9%
226.0 g/mol

% of N = 56.0   g/mol  x  100% = 24.8%
226.0 g/mol

% of O = 80.0    g/mol  x 100% = 35.4%
226.0 g/mol
Total percentage: 100%

Ex. 5 If a compound contains 21.6 grams of B, 57.0 grams of F, 80.8 grams of Ne, some amount of He, and has a total molar mass of 179.4, what is the percentage composition?
What is the molar mass of He?
179.4 - 21.6 - 57.0 - 80.8 = 20 <--- this is the molar mass of He.

% of B = 21.6   g/mol  x  100% = 12.0%
179.4 g/mol

% of F = 57.0   g/mol  x  100% = 31.8%
179.4 g/mol

% of Ne = 80.8   g/mol  x  100% = 45.0%
179.4 g/mol

% of He = 20.0   g/mol  x  100% = 11.1%
179.4 g/mol
Total percentage: 99.9%
(In this case, the total percentage was not 100% but was 99.9%.  It is just a 0.1% difference and not that big of a deal.  This is the result due to rounding.)

Video similar to Ex 2 & 3:

Video almost similar to Ex. 4 & 5

### More Mole Conversions

During class, we learned that there are more mole conversions.  You can convert from grams to particles!! Or moles to # of atoms in particles!! Seems like a lot...
The units in these conversions are:
-Grams
-Moles
-Particles/Atoms/Molecules/Formula Units
-# of Atoms in Particles

From Grams to Moles, you multiply using 1 Mole
MMg

From Moles to Grams, you multiply using   MMg
1 Mole
MMg = Molar Mass grams

From Moles to Particles/Atoms/Molecules/Formula Units, you multiply using
6.022 x 10^23 Particles
1 Mole

From Particles/Atoms/Molecules/Formula Units to Moles, you multiply using
1 Mole
6.022 x 10^23 Particles

From Particles/Atoms/Molecules/Formula Units to # of Atoms in Particles, you multiply using
# of Atoms
1 molecule

From # of Atoms in Particles to Particles/Atoms/Molecules/Formula Units, you multiply using
1 molecule
# of Atoms

Conversions from Particles to Mass
Ex. What is the mass of 2.78 x 10^22 Fe Atoms?
2.78 x 10^22 Fe Atoms x                 1 Mole                x      55.8 g (Molar Mass)
6.022 x 10^23 Fe Atoms                 1 Mole
= 2.58 g

Ex. What is the mass of 8.4 x 10^18 SO3 molecules?
8.4 x 10^18 molecules x                 1 Mole                 x 8.01 g (Molar Mass)
6.022 x 10^23 Molecules               1 Mole
= 1.1 x 10^-3 g OR 0.0011 g

Conversions from Grams to Particles
Ex. How many atoms of Iron in 20.0 g of Iron?
20.0 g x           1 Mole               x  6.022 x 10^23 Atoms
55.8 g (Molar Mass)               1 Mole
= 2.16 x 10^23 Atoms of Fe

Here is a video that demonstrates from Grams to Atoms (Skip to 4:10 in the video)

Ex. How many formula units of KMnO4 in 0.240 g of KMnO4?
0.240 g x 1 Mole    x  6.022 x 10 ^23
158.0 g             1 Mole
= 9.15 x 10^20 Formula Units

QUIZ NEXT CLASS (Nov.25) ON MOLE CONVERSIONS!!!!!
QUIZ HOOOOOOOOOOOOOOOOOOO! RIGHT ON! OKAYY!!!

### Mole Conversions

1. Conversions from particles <--> moles
(recall 6.022 x 10^23)

From particles --> moles
3.01 x 10^24 particles x (1 mole/ 6.022 x 10^23) = 5.00 moles

From moles --> particles/molecules/formula units
Ex. 0.75 moles of CO2 --> molecules
0.75 moles x (6.022x10^23/ 1 mole) = 4.5 x 10^23 molecules of CO2

Ex. 0.75 moles of CO2 --> atoms of Oxygen
4.5 x 10^23 molecules x 2 atoms of O = 9.0 x 10^23 atoms of oxygen.

2. Conversions between grams <-->moles

From moles --> grams
Ex. 2.04 moles of carbon --> grams
molar mass of Carbon = 12.0 g / mol
2.04 mole x 12.0 g/ 1 mole = 24.5 grams of Carbon

Ex. 0.341 moles of NO2 --> grams
Molar mass of NO2 = 46.0 g / mol
0.341 moles x (46.0 g / 1 mole) =  15.7 grams of NO2

Here is a video explaining how to convert moles to grams:

From grams --> moles
Ex. 3.45 grams of Carbon --> moles
Atomic mass of Carbon = 12 grams
3.45 grams x (1 mole / 12 grams) = 0.288 moles

Ex. 6.2 grams of MgCL2 --> moles
Molecular mass of MgCL2 = 95.3 grams
6.2 grams x (1 mole / 95.3 grams) = 0.065 moles

Here is a video explaining how to convert grams to moles:

### The Mole

Equal volumes of different gases have a constant ratio:
Oxygen             :  Hydrogen   16:1
Carbon Dioxide :  Hydrogen   21:1

Relative Mass:
-Expressed by comparing it mathematically to mass to the mass of another object.

-Equal volumes of different gases at the same temperature and pressure have the same number of particles.
-If they have the same number of particles, the mass ratio is due to the mass of the particles.
-We now use this principle for the relative masses of all atoms on the periodic table.

Atomic Mass:
-The mass of a specific isotope of a given atom. Expressed as amu (atomic mass unit)

Formula Mass:
All the atoms of a formula of an ionic compound.
Example:  Potassium Fluoride
K            +         F
39.1        +    19.0
KF = 58.1 amu

Molecular Mass:
-The mass of one molecule of a substance.  Expressed as amu.

Molar Mass
-Atomic/Molecular/Formula mass of any pure substance (in grams per mole)
Example: 1 mole of oxygen = 16.0 g/mol
1 mole of carbon = 12.0 g/ml
-The molar atomic mass of an element is the mass of 1 mole of that element.
This video explains how to find molar mass: