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ISOTOPES:

-Takes into consideration he whole mass (all isotopes), this can also be referred to as the relative
abundance

MASS NUMBER X PERCENTAGE + MASS NUMBERS
E.G.
(75X35)+(75=37)

100
=35.3
ISOTOPES ­ atoms of an element with different numbers of neutrons



RAM ­ RELATIVE ATOMIC MASS: (Ar)

RAM- calculates the…

Page 2

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=89%




RFM ­ RELATIVE FORMULA MASS: (Mr)

RFM- finds out the mass of the whole formula

1. Write the formula of the compound.
2. Write the numbers of each atom in the formula.
3. Insert the relative atomic mass for each type of atom.
4. Calculate the total mass for…

Page 3

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Fe (iron) O (oxygen)
Mass=44.8g 19.2g
Ar=56 Ar=16
Mass = 44.8 19.2
Ar 56 16
=0.8 =1.2

0.8 = 1 1.2 = 1.5
0.8 0.8

1x2 because it gives
a simpler number

=3


Ratio of Fe to O is 1:3



Using the EF to calculate the MF (and visa versa)…

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Examples question 2:
A compound containing 62.7% C, 10.33% H and 27.6% O. what is the MF if the Mr is 58.0%?

C H O
Mass 62.07 10.33 27.60
Ar 12 1 16
Mass 62.07 10.33 27.60
Ar 12 1 16
=2.6725 =10.37 =1.725


Divide them all by the smallest…

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