# molar-mass

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```					MOLAR MASS
Chapter 6, Section 2A
MASS OF CHEMICAL COMPOUNDS
 Like individual atoms, molecules have an mass.
 We can calculate the mass of a mole of any
molecule.
 We find the mass of molecules by adding the
adding the masses of the elements that make up
the molecule together.
 Example: What is the mass of one mol of CO2?
 Mass of 1 mol of C = 1 x 12.01 g = 12.01 g
 Mass of 2 mol of O = 2 x 16.00 g = 32.00 g
 Mass of 1 mol of CO2 = 42.01 g
MASS OF CHEMICAL COMPOUNDS
 The quantity that we just calculated is the molar
mass for carbon dioxide.
 The molar mass of any substance is the mass (in
grams) of 1 mol of that substance.
 The units of molar mass are g/mol

 You try:

 Calculate the molar mass of methane (CH4).
 Mass of 1 mol C = 1 x 12.01 g = 12.01 g
 Mass of 4 mol H = 4 x 1.01 g = 4.04 g
 Mass of 1 mole of CH4 = 16.05 g
 Molar mass = 16.05 g/mol
 Being able about calculate molar mass means
that you can calculate the number of atoms or the
number of moles in a molecule or compound.
 Use these steps (they should look familiar):

1. Find your starting and ending units

2. Calculate the molar mass of your compound

3. Identify the conversion factors you need. 1 mol
= 6.02 x 1023 molecules/atom, and 1 mol = mass
in grams of that substance
4. Set-up the problem so your units will cancel

5. Multiply the top, multiply the bottom, divide
the top by the bottom.
TYING IT TOGETHER
    How many moles are in a 5.69 g sample of NaOH
1.    Starting: grams; Ending: mol
2.    Calculate the molar mass of NaOH.
 1 mol Na = 22.99 g, 1 mol O = 16.00 g, 1 mol of H =
1.01 g.
 1 mol NaOH = 40.00 g

3.    Conversion factors: 1 mol = 40.00 g NaOH
4.    Set-up and Calculations

5.69 g       1 mol

40.00 g        = 0.142 mol NaOH
TYING IT TOGETHER
 Calculating how many molecules are in a sample.
 How many water molecules are in a 10.0 g
sample of water?
 Formula: H2O

1. Starting in: grams; Ending in: molecules

2. Calculate molar mass:
 2 mol H = 2 x 1.01 = 2.02 g H
 1 mol O = 1 x 16.00= 16.00 g O
 Molar mass = 18.02 g/mol
TYING IT TOGETHER CONT.
   Determining the # of moles:
10.0 g H2O      1 mol

18.02 g H2O            = 0.555 mol H2O

   Determining the molecules:
0.555 mol H2O           6.02 x 1023 molecules

1 mol H2O               = 3.34 x 1023 H2O
molecules

   You can have completed this as one long problem,
but I wanted to divide it up to show you the
smaller parts

```
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