Percent Composition

Percent Composition:
The percent composition of a compound is a relative measure of the mass of each different element present in the compound.



To calculate the percent composition (percentage composition) of a compound

1. Calculate the molar mass, MM, of the compound
2. Calculate the total mass of each element present in the formula of the compound
3. Calculate the percent composition: % by weight (mass) of element = total mass of element present ÷ molar mass x 100

Examples:

Calculate the percent by weight of sodium (Na) and chlorine (Cl) in sodium chloride (NaCl)

• Calculate the molecular mass (MM):

MM = 22.99 + 35.45 = 58.44

• Calculate the total mass of Na present:

1 Na is present in the formula, mass = 22.99

• Calculate the percent by weight of Na in NaCl:

%Na = (mass Na ÷ MM) x 100 = (22.99 ÷ 58.44) x 100 = 39.34%

• Calculate the total mass of Cl present:

1 Cl is present in the formula, mass = 35.45

• Calculate the percent by weight of Cl in NaCl:

%Cl = (mass Cl ÷ MM) x 100 = (35.45 ÷ 58.44) x 100 = 60.66%

    The answers above are probably correct if %Na + %Cl = 100, that is,  39.34 + 60.66 = 100.

http://www.youtube.com/watch?v=xbEeyT8nK84

By: Hikari Hoshika

HARDER Mole Conversions



(click to enlarge)



Conversions between: PARTICLES → MASS

E.g. WHAT IS THE MASS OF:  1.34x10²² Zn atoms?   

           

     1.34x10²² atoms  X  .  1 mole      . X      65.4g  .  =   1.46g  of Zn

                                                 6.022x10²³          1 mole

Conversions between: GRAMS → PARTICLES

E.g.  HOW MANY ATOMS WOUD YOU HAVE IF YOU HAVE 10.0g OF COBALT?

            10.0g   X     1 mole  .  X   6.022x10²³   =   1.02x10²³  atoms of  Co

                                      58.9g               1 mole

By: JZ

Mole Conversions

Refer to the mole map:

Particles ----> Moles

Ex.  How many moles of hydrogen molecules (H₂) are present in 9 x 10²³ molecules of hydrogen?

                                                                                  1 mole

9.0 x 10²³ molecules of hydrogen X  --------------------------------  =  1.5 moles

                                                                     6.022x10²³ molecules

*** Round to the correct significant figure!

Moles ---> Particles/Molecules/Formula units/atoms

Ex.  How many molecules are contained in 3 moles of water molecules, H₂O?

                           6.022x10²³ molecules

3.0 moles X  --------------------------------  =  1.8x10²⁴ molecules

                                       1 mole 

Moles ---> Grams

Ex.  Determine the mass in grams of 3.60 mole of H₂SO₄.

1. Find the molar mass of H₂SO₄.

H --> 1.0(2) =      2

S --> 32.1   =     32.1 +

O --> 16.0(4)=   64

                       ---------

                        98.1 g

     2.  Solve.

                           98.1 g

3.60 moles X  ------------  =  353g of H₂SO₄

                           1 mole 

♥  http://www.youtube.com/watch?v=NMdN1LtHuDA&feature

Grams ---> Moles

Ex.  How many moles of methane molecules, CH₄, are in 80 grams of methane?

C --> 12.0 =     12

H --> 1.0(4) =   4 +

                       ------

                        16 g

             

                 1 mole

80g X  ------------  =  5.0 moles

                  16g 

♥  http://www.youtube.com/watch?v=ehepBBtSbDc

By: Hikari Hoshika

Who wants some guacamole?

Unfortunately, I was kidding about the title


The mole = volumes of different gases, has a constant ratio.

 Amedeo Avogadro

His law states that equal volume of different gases at the same temperature and pressure have the same number of particles

So if the particles are the same then the mass ratio is the mass of the particles.

MOLAR MASS:

- molar mass can be used for atomic/molecular/formula mass and are written in the form of grams per mole (g/mol)

       ex. 1 mol of sodium = 23.0

Avogadro's number: 6.022× 10^{23  PARTICLES} 

                                                                                                           ^MOLE

^{Since Ms. Chen mentioned something about a mole day...}

^{http://www.youtube.com/watch?v=ReMe348Im2w}

not very original don't you think??

Post : JN

To Excel in Excel

Title basically means: to Exceed in Microsoft Excel
(If you didn't get it, it's fine. Not many people understood Kariodisonium-119 either)

Today, we went to the computer lab to learn(?) how to make a graph using Microsoft Excel.

Click here to see what we had to put on the graphs
So here's a video on how to make a graph using Microsoft Excel



By: JZ

LAB day. Measuring Thickness of Aluminum Foil

HOW TO FIND THE THICKNESS OF ALUMINUM FOIL

Remember the formula, 

                    

density = mass/volume

Also remember the formula, volume = length x width x height.  Thickness will substitute height, therefore making the formula, volume = length x width x thickness.  Since length x width = area, we could rewrite the density formula to: 

density of Al = mass of Al / area of Al x thickness of Al

The formula can be rearranged into:

thickness of Al = mass of Al / area of Al x density of Al

Information needed:

• length and width of aluminum square
• mass measured by a centigram measure

Exponential Error 

It expresses the future growth a very small error can become.

Formula:

Exponential error = your measurement - Accepted value / Accepted value x 100 --> %

 *It is written as a %

Accepted Value

A value of a substance accepted and approved by many

*given by instructor


By: Hikari H.

the knowledge of density can give oneself more knowledge

 formula for density is.. Density =Mass

                                                  volume

OR

V = m       OR     m = DV

       D

TIPS TO REMEMBER:
solid is g/cm3
liquid is g/mL
1 cm3 of water = 1mL

Density of water is 1000 g/L or 1.0 g/mL

If d of object is < than the d of liquid..then it should be floating on top

otherwise, it would be sinking!

Below is a colourful experiment involving density!

http://www.youtube.com/watch?v=7HNMiUH1Xkk

JN