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# Percentage yield AS question help :) watch

1. Hey, I'm having a problem with this question: Ethanol (molar mass 46g/mol) is manufactured by the hydration of ethene (molar mass 28g/mol): C2H4 + H20 ---> C2H5OH.

In a typical process 28 tonnnes of ethene produces 43.7 tonnes of ethanol. The percentage yield for the process is:

A :64% B :95% C:100% D :156%

The answer(according to the edexcel mark scheme) is 95%. I thought it was 100% because only 1 product is formed? How do you calculate 95%? Thanks everyone
2. (Original post by polaritymolecule)
Hey, I'm having a problem with this question: Ethanol (molar mass 46g/mol) is manufactured by the hydration of ethene (molar mass 28g/mol): C2H4 + H20 ---> C2H5OH.

In a typical process 28 tonnnes of ethene produces 43.7 tonnes of ethanol. The percentage yield for the process is:

A :64% B :95% C:100% D :156%

The answer(according to the edexcel mark scheme) is 95%. I thought it was 100% because only 1 product is formed? How do you calculate 95%? Thanks everyone
You calculate the theoretical mass that could be produced given the quantities used.

You do this using the molar realationship in the equation.

20 tonnes ethene = 28,000,000 g = 28,000,000/28 = 1,000,000 moles

This should theoretically produce 1,000,000 moles of ethanol = 46,000,000 g

BUT you only produce 43.7 tonnes

So the percentage yield = 100 * actual yield/ theoretical yield = 100 * 43.7/46 = 95%

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