5. Formula and amounts (YIELD + ECONOMY)
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What is a percentage yield
The amount of product you get from the reaction.
Give the equation to calculate percentage yield
Actual yield / theoretical yield x 100
Why is actual yield ALWAYS LESS than theoretical yield
• side reactions • incomplete reaction • impurities • loss of product in apparatus
What is atom economy
A measure of how many atoms (in terms of atomic mass) in reactants end up in your desired product. measures EFFCIENCY wheras percentage yeild does not
Give the equation to calculate atom economy
Mr of desired products / Mr of all products x 100 (include the big numbers)
Give 2 reasons why having a higher atom economy ( closer to 100%) is good
More efficient so less wastage Less by product
X g of a chemical is reacted, process has a 72% yield - calculate the mass of the product made
1) Calculate the moles of the reactant used 2) Use the mole ratio to calculate the moles of product as if 100% yield 3) Then multiply by 0.72 to factor in yield to scale down for the moles actually produced 4) Times moles by Mr to get mass
A process has a 72% yield - calculate the mass of a reactant required to make X g of a product
1) calculate the moles of product being made 2) use mole ratio to calculate moles of reactant as if 100% yield 3) Then divide by 0.72 to factor in yield to scale up for the moles required 4) Times moles by Mr to get mass