# Chemistry

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• Created by: Katie
• Created on: 13-03-13 18:39

## Amount of substance

Relative Atomic Mass - the ratio of the average mass per atom of the naturally occurring form of an element to one-twelfth the mass of an atom of carbon-12.

Relative Molecular Mass - the sum of all the relative atomic masses of the atoms in a molecule; the ratio of the average mass per molecule of a specified isotopic composition of a substance to one-twelfth the mass of an atom of carbon-12

The Mole                          Mass
6x10(23)                  Moles x Molar Mass

Mass of CO, burning carbon with 16g of Oxygen?
1) Write balanced equation                            2C + O2 -> 2CO
2) Work out how many moles?                    2 moles C + 1 mole O -> 2 moles CO
3) Moles of ?element?                                  O2= mass/molar mass (16/32= 0.5 mol)
4) Moles of wanted in q?                    1 mole of O2, 2 moles of CO so moles O2 x 2 = 1 mole
5) Convert moles to mass.        Mass = moles x molar mass= 1 x(12+16) = 28g

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## Moles continued

1 mole of gas at room temperature and pressure is 24dm(3)

Moles and concentration
1 mole of a substance dissolved in 1dm(3) of water has a concentration of 1mol/dm(3)

Moles
Volume(dm3) / Concentration(mol/dm3)

Number of atoms in 12g of carbon-12

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## Ideal Gas Equation

PV=nRT
P = pressure (Pa, Nm-2)
V = volume (m3)
T = temperature (K) Always change to Kelvin +273
n = moles

R = 8.31 (JK -1 mol -1)

Volume = V=nRT
P

Moles = n=PV
RT

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## Empirical and Molecular Formulae

Empirical formulae - the simplest ratio of atoms of each element in a compound
1) Find the masses of each element present
2) Work out the number of moles of each element
moles = mass of element
mass of 1 mol of element

3) Convert the number of moles into a whole number
Molecular formulae - actual number of atoms of each element in one mole of the compound
Relative molecular mass
Relative mass of empirical formulae

Percentage by mass
1) atomic masses for the elements
2) how many grams of each element are present in one mole of the compound
3) work out mass of one mole
4) divide atomic mass by mass of one mole and times by 100

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## Atom Economy

% Atom Economy = mass of desired product   x 100
total mass of reactants

Yield of a chemical reaction =

the number of moles of a specific product                   x 100%
theoretical maximum number of moles of the product

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