Density

* Density is a measure of mass / volume
* When calculating density the following chart makes the task a lot easier to understand…


Density
* (D = m / v)
(Molar Mass) (Molar Volume)
Mass ------ Moles ------ STP

*
(Avogadro’s #)

Molecules
*
(Subscripts)
*
Atoms


* Here are some examples / solutions to density problems:


Ex. Compound “X” has a density of 3.0 g/ml. Determine the mass of 12 mL of X. How many moles are in 12 mL of X…?

Step # 1. 12 mL x 3g /1 mL = 36g


Step # 2. H2O ~ 2(1.0) + 16.0 = 18.0g


Step # 3. 36g x 1 mol / 18.0g = 2.0 mol


Ex. An unknown compound has a molar mass of 73.0 g/mol. If 0.15 mol occupies a volume of 50 mL, determine the compound’s density.

Step # 1. 0.15 mol x 73.0g / 1mol = 10.95g

Step # 2. 10.95g / 50mL = 0.219 g/mL ~ 0.22 g/mL

Cool Video :)

Moles to Atoms

To go to atoms from moles you must use Avogrado's number (6.02 x 10^23)

1. How many atoms are in 1.5 mol of Iron:

     1.5 mol x 6.02x 10^23 atoms = 9.0 x 10^23 atoms
                           1 mol

2. How much water molecules are there in 0.65 mol?

    0.65 mol x 6.02 x 10^23 molec  = 3.9 x 10^23 molec
                            1 mol

3. How many H2, Hydrogen atoms are there? How many Oxygen atoms? In H20

   i) 3.9 x 10^23 molec x 2 atoms = 7.8 x 10^23 atoms
                                         1 molec

  ii) 3.9 x 10^23 molec x 1 atoms  = 3.9 x 10^23 atoms
                                         1 molec

4. A cylinder of Helium contains 4.6 x 10^30 atoms. How many moles of Helium?
      4.6 x 10^ 30 atoms x 1mol   = 7.6 x 10^6 mol
                                       6.02 x 10^23 atoms


How many C atoms? How many H atoms? How many O atoms? How many in total? in CH3COOH?

1. 3.0 x 10^24 molec x 2 C atoms  = 6.0 x 10^24 C atoms
                                       1 molec

2. 3.0 X10^24 molec x 4 H atoms  = 1.2 x 10^25 H atoms
                                       1 molec

3. 3.0 x 10^24 molec x 2.0 atoms = 6 x 10^24 O atoms

4. 6.0 x 10^24 + 1.2 x 10^25 + 6 x 10^24 atoms = 2.4 x 10^25 atoms

Mole Conversions

Mole Conversions:
(Converting between Grams and Moles)


* To convert between moles & mass we use molar mass as the conversion factor
* Be sure to cancel the appropriate units!
* Use the chart below to help you with your conversions

Density
* (D = m / v)
(Molar Mass) (Molar Volume)
Mass ------ Moles ------ STP
*
(Avogadro’s #)

Molecules
*
(Subscripts)
*


Atoms

Ex. How many grams are there in 3.0 mol of O2?
* O2 = 2 x 16.0 ~ 36g / mol
* 3.0 mol x 32g / 1mol = 96.0g


Ex. Determine the # of moles of C5H12 that are in 362.8g of the compound.
* 5(12.0) + 12(1.0) = 72g / mol
* 362.8g x 1mol / 72g = 5.039mol


Ex. How many moles of magnesium bromide contain 5.38 x 10^24 formula units?
* 5.38 x 10^24molec x 1mol / 6.02 x 10^23molec = 8.39mol


Ex. Find the mass of 0.89mol of CaCl2.
* 40.1 + 2(35.5) = 111.1g / mol
* 0.89mol x 111.1g / 1mol = 99g


Ex. Find the mass of 0.159mol of SiO2.
* 28.1 + 2(16.0) = 60.1g / mol
* 0.159mol x 60.1g / 1mol = 9.56g

Percent Composition

Don't worry! we have easy instructions on how to plow through percent composition and become a professional at it! (:

Percent Composition - The percent composition of a component in a compound is the percent of the total mass of the compound that is due to that component.

****The percentage by mass of an element in a compound is always the same*****

To find the percentage by mass, determine the mass of each element present in one mole.

The percent composition (percentage composition) of a compound is a relative measure of the mass of each different element present in the compound.




To calculate the percent composition of a component in a compound:


1. Find the molar mass of the compound by adding up the masses of each atom
in the compound using the periodic table.
2.Calculate the mass due to the component in the compound you are for which you are solving by adding up the mass of these atoms.
3.Divide the mass due to the component by the total molar mass of the compound and multiply by 100.

Remember this!

Percent composition = mass due to specific component/ total molar mass                                                    of compound x 100%

here's a video on percent composition

Molar Volume

 STP?

• standard temperature (0°C) or (273.15 k) and pressure (1 atmosphere)  
• where one mole of gas occupies 22.4L 

Molar Volume?

• the volume occupied by one mole of gas

 How to find Molar Volume

Conversion from Moles to Molar Volume

Conversion from Molar Volume to Moles

Isn't that a simple task!?

Here is an online worksheet with some questions! don't look at the answers before you're finished so you can challenge yourself! (:

Molar Volume worksheet!

Do questions 6, 9, 10, 11 and 12

Here's a game you can play with Molar Volume!

FUN GAME! (:

Molar Mass

• The mass (grams) of 1 mole of a substance is called the molar mass
• It can be determined from the atomic mass on the periodic table
• Measured in g/mol

So what exactly is Molar Mass? 
 Molar mass is the atomic weight of an element expressed in grams is the mass of 1 mole of element.


How do you determine Molar Mass in a Compound?
To determine the molar mass of a compound you must ADD all the mass of the atoms together

Here's an explanation that will help you understand what Molar mass is:
 Follow these steps to find molar mass! What is the molar mass of H20? (water)

1. Identify how many atoms of each of the elements are in the chemical formula. In the example there are 2 atoms of Hydrogen and there is 1 atom of Oxygen.
2. Look at the periodic table and search for the elements given & then look at each of their atomic masses. The elements in H20 are Hydrogen and Oxygen. The atomic mass for Hydrogen is 1.0 amu and the atomic mass for Oxygen is 16.0 amu
3. Now multiply the number of atoms found in the chemical formula with the atomic mass.                        2 atoms of Hydrogen --->2(1.0) + 1atom of Oxygen-----> 16.0= 18.0 g/mol

So now that you have a basic foundation of what Molar Mass is now its YOUR TURN to do some practice problems! Answers will be provided at the bottom of the last question. ( but don't look straight into the answers you need to TRY some problems and then check if u understand it)  :)

• What is the molar mass of NO2?

• What is the molar mass of NaCl?

• What is the molar mass of FeO?

• What is the molar mass of NaNO3?

Answers:
NO2: 14.0 + 2(16.0)= 142.1 g/mol
NaCl: 23.0 + 35.5= 58.5 g/mol
FeO: 55.8 + 16.0= 71.8 g/mol
NaNO3: 23.0 + 14.0 + 3|(16.0)= 85 g/mol


Mole Conversions
To convert between moles & mass we use molar mass as the conversion factor. You must also be sure to cancel the appropriate units.

Here's an example: How many grams is there in 1.5 mol of 02?


1.5 Mol x     32.0   g   = 48.0 g
                     1 mol

Now you TRY!

How many moles are there in 115g of Fe203?


A sample of HCL contains 0.54 mol. How many grams of HCl is this?

Avagadro's Number and the Mole:

As we know, atoms and molecules are extremely small and microscopic objects contain too many of them to count or weigh individually. 

However, Amedeo Avogadro proposed a solution to this problem...

• the # of atoms in 12.00000 g of Carbon would be equal to a constant (this is = to 1 mole of carbon).
• this value is now called Avagadro's # and forms the basis of all quantitative chemistry

 So what is Avagadro's #?

1 Mole = 6.02 x 10^23


But What's a Mole?  

A mole is simply a multiple of things  

• 1 pair = 2
• 1 dozen = 12
• 1 century = 100  years
• So... 1 mole = 6.02 x 10^23              

How Big is a Mole?

• 1 mole of meters would cross the entire galaxy!
• $mole would be enough to give every person on earth 1 million billion dollars

You can also identify 1 mole as 602 000 000 000 000 000 000 000... 

                                                                             
Particle                                                                 
Atom:         Element            6.02 x 10^23
                                                 1 mole        Fe     
Molecule:   Covalent           6.02 x 10^23
                   Compound            1 mole        CO2  
Formula      Ionic                6.02 x 10^23
Unit:           Compound            1 mole        NaCl 

^ Example of using the mole:

• A sample of Carbon contains 3.78 x 10^24 atoms.  How many moles of carbon is this?

1. 3.78 x 10^24 atoms x 1 mole / 6.02 x 10^23 atoms
2. 3.78 x 10^24 / 6.02 x 10^23 (when doing this equation on your calculator you want to press "2nd ," which gives you EE.  This replaces the 10 and gives you a more precise answer)
3. this equation cancels out the unit atoms leaving us with the amount of moles...
4. thus your final answer is 6.28 moles

Another Example:

• Say you have 15.25 moles in a compound.  But you want to know the amount of molecules in the substance.  How would you solve this problem? 

1. 15.25 moles x 6.02 x 10^23/ 1 mole 

• But how did we figure our the ratio of molecules to moles?  You look at the chart above the first example!  Simple as that.  

    2.  15.25 moles x (6.02 x 10^23)... don't forget to use the "2nd ," instead of "x 10"
    3.  this equation cancels out the unit for moles and leaves you with the amount of molecules in the 
         substance 
    4.  your final answer is 9.1805 x 10^24 molecules