Amount of Substance
Amount of substance, n
n = mass / Mr
Solution calculations
The concentration of solutions are measured in mol dm-3
c= concentration in mol dm-3
V = volume in cm3
n = Vc / 1000
Many people find equations like this difficult to remember. You may prefer to remember an easy, obvious sentence and then learn how to use it.
Remember: "One litre of a one mole per litre solution contains one mole."
To find the number of moles in 15.6 cm3 of a 3.5 mol dm-3 solution.
1 dm3 of a 1 mol dm-3 solution contains 1 mole
1 cm3 of a 1 mol dm-3 solution contains 1/1000 mole
15.6 cm3 of a 1 mol dm-3 solution contains 15.6/1000 mole
15.6 cm3 of a 3.5 mol dm-3 solution contains 15.6 x 3.5/1000 mole
It is a bit longer but it is easier to follow......you decide what is best for you.
The Ideal Gas equation
Avogadro said that: providing that the pressure and temperature of gases are the same, equal volumes of two gases can be assumed to have the same number of moles.
At GCSE you may have used "1 mole of gas occupies 24 dm3 ". Strictly, this should have been quoted as being at 25oC and 1 atmosphere pressure.
The ideal gas equation takes all of this into account
pV = nRT
p is the pressure in Pa (normal atmospheri pressure is about 100 kPa)
V is the volume in m3 (There are 1000 dm3 in 1 m3)
T is the temperature in Kelvin (0 oC is 273 K)
R= 8.31 JK-1 mol-1
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