# Chemistry equations (unit 2)

Hope this helps you to remember some of the equations we need to learn, there are SO many !!

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• Created by: Jemima
• Created on: 22-05-12 12:41

## Number of moles

Number of moles   =           Mass in g (of element or compound)

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Mr (of element or compound)

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## Percentage mass of an element in a compound

Percentage Mass of an Element in a Compound =

Ar x No of atoms (of that element)

-----------------------------------------           x100

Mr (of whole compound

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## Finding the empirical formula

• List all the elements in the compound
• Underneath them write experimental masses or percentages
• Divide each mass or percentage by the Ar for that element
• Turn numbers you get into simple ratio by dividing by the smallest number or multiplying
• Get the ratio in the simplest form

BOOOM ITS AS EASY AS THAT!

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## Calculating masses in reactions

• Write out the balanced equation
• Work out the Mr (just for the two bits you want)
• Apply the rule; DIVIDE TO GET ONE THEN MULTIPLY TO GET ALL

SIMPLES

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## Percentage Yield

Actual yield (grams)

--------------------------------        x100

Predicted yield (grams)

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## Rate of reaction

Amount of reactant used or amount of product formed

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Time

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