Converting Between Volume and Moles!

Last class we learned how to convert between grams and moles. Today, we learned how to convert between volume and moles. The volume, in this case, is that of a gas.

 At a specific pressure and temperature, one mole of any gas occupies the same volume.

This standard is: At 0^oC and 101.3kPa...

...1 mol = 22.4L

From this, we can assume that the volume occupied by one mole of oxygen gas is the same as the volume occupied by one mole of hydrogen gas, at the standard temperature and pressure (STP).
Thus, 22.4L/mol is the molar volume at STP. Memorize this number!



EXAMPLES
-How many litres will 2.5mol of H_2(g) occupy at STP?
2.5mol x 22.4L/1mol = 56L


-A certain gas is found to occupy 11.6L at STP. How many moles of gas are there?
11.6L x 1mol/22.4L = 0.51786mol or 0.518mol(to three significant digits)


-At a temperature and pressure where molar volume is 45.0L/mol...?
11.6L x 1mol/45.0L = 0.2578mol or 0.258mol (to three significant digits)


-At STP a sample of Oxygen gas contains 11.5mol. How many litres of oxygen gas are there?
11.5mol x 22.4L/1mol = 257.6L or 258L (to three significant digits)


-At STP an unknown gas (note that the fact that the gas is "unknown" does not make a difference) is found to occupy 150mL. How many moles of gas must there be?
150mL x 1L/1000mL = 0.150L
0.150L x 1mol/22.4L = 0.006696428mol or 0.00670mol (to three significant digits)


-Solve the above using an alternative method.
150mL x 1mol/22.4L = 6.70mmol or 0.00670mol


-A certain amount of Chlorine gas occupies 1.6L. Find the number of moles present and then determine the mass of Chlorine.
35.5 (refer to Chlorine in the periodic table for this number) + 35.5 (because Chlorine is diatomic) = 71.0
1.6L x 1mol/22.4L = 0.07143mol or 0.071mol
0.071428571mol x 71.0g/1mol = 5.071428571 or 5.1g (to two significant digits)




 Next time: Molar Volume Lab!