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Slide 1

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Calculations... Double award
Remembering the formulas, putting numbers in... This
sounds like Maths to me. If you are good at Maths then
this will be a breeze. If you are not its just putting
numbers in a calculator.
So click on to find out more…read more

Slide 2

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There is something you need to know:
Ar = relative atomic mass
Mr = relative molecular mass/relative formula mass
Basically all atoms are relative (compared) to Carbon.
The relative atomic mass will be given in the question, you don't need to remember
For a compound:
To get the relative molecular mass you need to add the relative atomic
mass of all the elements.
E.g. Work out the molecular mass of Cu(OH)2 Given in the exam:
Ar of Cu = 64 Cu (Copper) = 64
Ar of O x 2 = 16 x 2 =32 O (Oxygen) = 16
Ar of H x 2= 1 x 2 =2 H (Hydrogen) = 1
Mr Cu(OH)2 = 98
Times two because it is inside the
bracket…read more

Slide 3

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If you didn't know it before well you know now!
Bracket ­ multiply everything inside
- only applies to the number
________ 4 ___________3
of the element on the left
2______________- number in front applies
to the whole formula in this case its two…read more

Slide 4

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The Mole
1 MOLE of any substance contains the same number of particles
If you must know its 6.02 x 10^23 (^ = to the power of)
a mple
NaCl [ Sodium Chloride]
Ar of Na (Sodium) = 23
Ar of Cl (Chlorine) =35 .5g
1 Mole of Sodium Chloride is 58.5g
Basically it has a unit on the end such as gram.
A'1M' solution contains one mole dissolved into one litre…read more

Slide 5

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Percentage mass
Relative atomic mass
Total relative molecular mass x 100
x a mple
An e
Percentage mass of Magnesium in Magnesium Oxide
Relative atomic mass of Magnesium = 24
Relative atomic mass of Magnesium Oxide = 24 + 16 =40
X 100 = 60 % Ar of Mg = 24
Ar of O = 16
So Magnesium makes up 60% of the mass of the
compound…read more

Slide 6

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An exam question on percentage of mass
Find the percentage mass of Nitrogen in Ammonium Nitrate
Relative molecular mass of Ammonium Nitrate is 80
Relative atomic mass of Nitrogen is 14 x 2 =28 [two Nitrogens]
80 X 100 = 35%
35% of Ammonium Nitrate is made of Nitrogen and makes up more than
1/3 of the compound as Nitrogen provides more green, healthier leaves fir
greater development.…read more

Slide 7

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