391880
Description
Mind Map by emilywebber98, updated more than 1 year ago
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Created by emilywebber98
about 11 years ago
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Percentages and Formula
- Percentage Composition
- use the RAMs of the
elements in the
compounds and it's
formula to work this out
- EXAMPLE
QUESTION: find the
percentage of
magnesium in
magnesium oxide?
- Step 1: find the formula of the compound
(MgO) and then find the relative formula
mass of the elements and then the
compound ( Mg = 24 O= 16, 24 + 16 = 40)
- Step 2 : So 24g in 40g of MgO is Mg so you need to find
the fraction of this i.e. mass of element/mass of
compound
- Step 3: To finish it all of you need to find the percentage
(24/40 x 100= 60%)
- Step 1: find the formula of the compound
(MgO) and then find the relative formula
mass of the elements and then the
compound ( Mg = 24 O= 16, 24 + 16 = 40)
- use the RAMs of the
elements in the
compounds and it's
formula to work this out
- Empirical Formula
- Step 1: change the percentages
given to masses of each element
in 100g of the compound
- 75 % Carbon and 25% Hydrogen =
75g Carbon and 25g Hydrogen
- 75 % Carbon and 25% Hydrogen =
75g Carbon and 25g Hydrogen
- Step 2: Change the
masses to moles of
atoms by dividing the
masses by Ar values
- This tells you the ratio
of atoms of the different
elements in the
compound
- For carbon: 75/12 = 6.25 moles,
For Hydrogen: 25/1 = 25 moles
- This tells you the ratio
of atoms of the different
elements in the
compound
- Step 3: Then the simplest
whole numbers ratio gives you
the empirical formula of the
compound
- 6.25:25 = 1:4 so the formula is CH4
- 6.25:25 = 1:4 so the formula is CH4
- Step 1: change the percentages
given to masses of each element
in 100g of the compound
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