AQA AS CHEM1 - Amount of Substance Notes

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Amount of Substance
The Mole
Definition of a mole: The amount of substance that contains as many particles as there are in
12g of carbon-12 atoms.
Can also be described using Avogadro's constant - 6.023 X 1023 (this does not need to be
MR = Molar Mass.
Molar mass (MR) is the same as relative molecular mass ­ eg MR of CO2 = 12 + (2 x 16) = 44.
Mass of Susbstance = MR x No. of Moles
No. of Moles = Mass of Substance/MR
Number of Moles = Concentration x Volume (in dm3)
(1dm3 = 1000cm3)
Ideal Gas Equation
pV = nRT
p = pressure (Pa)
V = volume (m3)
n = number of moles
R = gas constant (8.31 J K-1 mol-1) ­ this is always given in questions
T = temperature (K)
Conversion Units
1 kPa = 1000 Pa
1 cm3 = 1 x 10-6 m3
1 dm3 = 1x10-3 m3
C + 273 = K
Remember: When dealing with questions about gases, volume is in m3 - when
dealing with questions on concentration of solutions, volume is always in dm3. Try
and remember that gases take up a larger volume, so use a larger unit.

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Formulas, Yield, Atom Economy
Empirical Formula = Smallest whole number ratio of atoms of each element in a
Molecular Formula = Actual number of atoms of each element in a compound
Eg: Hexane ­ Molecular Formula = C6H14
Empirical Formula = C3H7 (divided by 2)
Percentage Yield = Actual Yield x 100
Theoretical Yield
Atom Economy = Mass of Desired products x 100
Total Mass of Reactants…read more


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