Density and Moles

We told you how to convert from mass to moles and from moles to molecules, we event told you how to convert from mass to molecules. You thought you were finally finished, well you're not!
There's also Density.
Density or is measured in g/L or other variations such as kg/mL
well that's it for the non-gas density notes, how about a few example
How many moles are contained when the density of Li₂ O is 3.5 g/mL and the mass is 15 mL
15 mL  x           1 mol            = 29.9 mol
                 (2x6.94)+16.00

Thus you can now add this on to your growing number of possible conversions, exciting right?
Density of Gases
it's slightly different, you get a new formula (because we all love more new formulas)
molar mass over molar volume
  MMg/mol    = density g/L
22.4 L/mol

Oh boy, more examples!
Flourine gas at STP, find the density
2(19.00)g/mol  = 1.70 g/L
  22.4 L/mol

Now I want you to find the density of one Flourine at STP
1.70g/l  = 0.850 g/L (ridiculously simple)
    2

And so I leave you with a comic, so you can sit in your chair laughing while I go to sleep.
But remember conversions are important.

Moles to Volume

Finally, it's the long awaited post of MOLES TO VOLUME!!!!
Okay one quick thing you need to know
1 mole of any gas has the exact same volume at a specific temperature and pressure.
And what is this temperature and pressure you may ask?
At 0˚Celsius and 101.3 KPa 1 mole takes up 22.4 L
Very important stuff, however it's all very clear isn't it

Now on to the examples

What would you do if you had 3.2 L of some random unknowns substance we pulled out of a hat and you needed to figure out how many moles there are.

1.6 L x    1 mol      = 0.071 mol

              22.4 L

Now just to switch it up, let's say you had 7.2 mol of Ne, how many L of Ne are there at Standard Pressure and Temperature(STP)

7.2 mol  x    22.4    = 161.28 

                  1 mol

Making the answer (with significant digits) 1.6 x 10²

Mole to Atom/Molecule conversions

Today we learned how to convert, for example 2 moles of Iron into atoms.
To do this we cross multiply using avagadros number:

2 mol Fe x 6.02*1023    = 1.2*10 24 atoms of Iron
                      1 mol
This is just one of the many conversions we can do with avagadros number. Here are some more:


How many moles are present in 3.9*10 25 Nitrogen atoms?

3.9*10 25 Nitrogen atoms x 1 mol            = 64.8 moles
                                          6.02*10 23
or How many hydrogen atoms are there in 5.2 molecules of H2O?

5.2*10 13 molecules H2O x 2 Hydrogen atoms  = 2.6*10 13
                                          1 molecule H2O

These are just some of the different conversions we can do with moles!!!



Happy Calculating!!!!