# Quemedices

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Relative atomic masses, Moles, and mole calculations, p54-66

The masses of atoms are all different, but have to be compared to SOMETHING. That "something" is carbon. Carbon weighs exactly 12 unitsRelative atomic mass, Ar: the weighted average mass of all the isotopes in COMPARISON to carbon-12
(basically, the atoms mass number!)

Relative formula mass, Mr: (sometimes called relativemolecular mass). Used when talking about masses of COMPOUNDS, in comparison to carbon-12.
To find the Mr of a compound, simply add up their relative atomic masses. (Mr is unitless)
e.g. MgCO3
Mr = Mg =1 x 24
C = 1 x 12
O = 3 x 16
= 84
Find the Mr of the following compounds:
|1. CuO | |6. Al2O3 ||
|2. KI | |7. Al(OH)3 | |
|3. NaCl ||8. (NH4)2SO4 | |
|4. SO2 | |9. SO2 ||
|5. H2SO4 | |10. Al2(SO4)3 | |

1. 80
2.166
3.58.5
4. 64
5. 98
6. 102
7. 78
8. 132
9.461
10. 342

The mole p59-61
The "mole" is simply the measure of amount of substance.
In the following equation:
CH4 + 2O2 > CO2 + 2H2O
there are/is 1 mole of CH4
2 moles of O2
1 mole of CO2and 2 moles of H2O

1 mole of ANY substance is its relative formula mass, Mr, expressed in GRAMS

1 mole of CH4 = 16g
1 mole CO2 = 44g
but 2 moles of H2O = 36g (there are 2 x 18)

AND: 2 molesof O2 (NOT just O), each O has mass 16, so 2 x O=O (= 4 x 16) = 64g.
One O atom is 16g but one O2 MOLECULE is 32g

The above equation (and all equations) show that during a chemical reaction,...