Moles to Atoms/Molecules, Multistep Conversions and Density

Moles to Atoms/Molecules
Example: How many atoms are there in 1.3 moles of Iron?

Fe  1.3mol x  6.02x10²³atoms = 7.8x10²³ atoms 
                            1 mol

Multistep Conversions
Example: 11.5g of H2 are placed in a balloon at STP. Determine the volume of the balloon


11.5g  x  1 mol  x  22.4L = 129L
               2.0g       1 mol

Example: A cartire contains 25.0L of Nitrogen Gas at STP. How many grams of Nitrogen?

25.0L x 1 mol  x  28.0g = 31.3g
             22.4L     1 mol

Density
-Density is a measure of mass per volume d = m
                                                                      v
-Measured in either g/L or g/mL

Example: H20 has a density of 1.0g/mL. Determine the mass of 11.5mL of water. How many moles are in 11.5mL of water.

1.0g  x  11.5mL  = 11.5g = 12g
 mL

11.5g  x  1 mol  =  0.64mol
              18.0g 

Example: An unknown compound has a molar mass of 65.0g/mol. If 0.25mol occupies a volume of 50 mL, determine the compounds density

0.25mol  x  65.0g  =  16.25g
                  1 mol

16.25g  =  0.325g/mL  =  0.33g/mL
50mL