Multistep Mole Conversions!

Today Mr. Doktor wasn't there for class as he wasn't feeling well so we were forced to look at multistep conversions by ourselves. Not to worry though, we managed!


By now, we have a very handy map that can help to guide us on our journey to master the science of chemistry - particularly conversions involving the mole. It should look something like this:

As a review, to convert from mass to moles or moles to mass, we use molar mass; to convert from moles to volume or volume to moles, we use 22.4L/mol (@ STP); to convert from moles to molecules or molecules to moles, we use Avogadro's number; and to convert from molecules to atoms or atoms to molecules, we use the subscripts. Complete conversions usually involve more than one step. Shall we take up some examples?


EXAMPLES
-11.5g of H₂ gas are placed in a balloon at STP. Determine the volume of the balloon.
11.5g x 1mol/2.0g x 22.5L/1mol = 129L


-A car tire contains 25.0L of Nitrogen gas at STP. How many grams of Nitrogen is this?
25.0L x 1mol/22.4L x 28.0g/1mol = 31.3g


-How many formula units are there in 3.5g of Nickel (II) oxide?
3.5g x 1mol/74.7g x (6.02 x 10²³)molec/1mol = 2.8 x 10²²FU


-A sample of Oxygen gas contains 3.5 x 10²¹ molecules. How many grams of oxygen is this?
3.5 x 10²¹molec x 1mol/(6.02 x 10²³)molec x 32.0g/1mol = 0.19g


-A container holds 35.0L of Methane gas at STP. How many molecules of Methane is this?
35.0L x 1mol/22.4L x (6.02 x 10²³)molec/1mol = 9.41 x 10²³


-3.5 x 10²³ Chlorine atoms are present in a sample of Chlorine gas. How many litres of gas at STP is this?
3.5 x 10²³atoms x 1molec/2atoms x 1mol/(6.02 x 10²³) x 22.4L/1mol = 6.5L


-Determine the mass of 10 molecules of Carbon dioxide.
10molec x 1mol/(6.02 x 10²³)molec/1mol x 2atoms/1molec = 7.3 x 10^-22g


-A sample of NO₂ occupies 7.50L. How many Oxygen atoms are present in this sample?
7.50L x 1mol/22.4L x (6.02 x 10²³)molec/1mol x 2atoms/1molec = 4.03 x 10²³atoms


 
Next time: Mole Ratio Lab!