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.

Avogadro's Hypothesis:
-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:


Avogadro's Number
-The number of particles in 1 mole of any amount of substance is 6.022 x 10^23 particles/mol

-The mole is important because it allows chemist to count atoms and molecules 


A chemistry song

Density of Cold and Hot Water

The class went to the crick lab and were presented with a open office document that displayed numbers.  The next step was input the formula for density.  What would happen was that the formula used to calculate the density and it was then displayed on the graph.  Then we would change the colors of the graph to our personal preferences, add a title, and label the x and y axis.  Then we saved the file and handed it into  Mrs. Chen's handin folder.

density