To calculate the percentage of an element in a com
- Write down the formula of the compound
- Using the Ar values from your data sheet, work out the Mr of the compound. Write down the mass of each element making up the compound as you work it out.
- Write the mass of the element you are investigating as a fraction of the Mr
- Find the percentage by multiplying your fraction by 100
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To work out the formula from percentage masses:
- Change the percentages given to the masses of each element in 100g of compound.
- Change the masses to moles of atoms by dividing the masses by the Ar values. This tells you how many moles of each different element are present.
- This tells you the ratio of the different elements in the compound.
- Then the simplest number ratio gives you the empiricalformula of the compound.
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