# ALEVEL CHEM alkenes exam q

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#1
Hi, I'm struggling with an exam question. Here it is:

Ethene, C2H4, was prepared from ethanol, C2H5O8, by the following reaction
C2H5 OH –> C2H4 + H2O
A chemist reacted 9.2 g of ethanol, C2H5OH, and obtained 4.2 g of ethene. Calculate the percentage yield of ethene in the reaction.

I don't understand how to find the percentage yield as I am unsure how to find the theoretical yield – I found that the RMM of ethene is 28. thank you so much for your help!
1
1 year ago
#2
(Original post by lane_in_pain)
Hi, I'm struggling with an exam question. Here it is:

Ethene, C2H4, was prepared from ethanol, C2H5O8, by the following reaction
C2H5 OH –> C2H4 + H2O
A chemist reacted 9.2 g of ethanol, C2H5OH, and obtained 4.2 g of ethene. Calculate the percentage yield of ethene in the reaction.

I don't understand how to find the percentage yield as I am unsure how to find the theoretical yield – I found that the RMM of ethene is 28. thank you so much for your help!
So you have found the RMM of ethene which is 28.

Find the RMM of C2H5OH.

Find the number of moles of C2H5OH using the relation
number of moles = mass / molar mass
From the equation, deduce the number of moles of ethene you would theoretically get. Then the relation

mass = number of moles x molar mass
should be used to find the theoretical yield.

Finally, the relation

percentage yield = actual yield / theoretical yield x 100%

gives the final answer. Note that the actual yield is 4.2g.
0
#3
(Original post by golgiapparatus31)
So you have found the RMM of ethene which is 28.

Find the RMM of C2H5OH.

Find the number of moles of C2H5OH using the relation
number of moles = mass / molar mass
From the equation, deduce the number of moles of ethene you would theoretically get. Then the relation

mass = number of moles x molar mass
should be used to find the theoretical yield.

Finally, the relation

percentage yield = actual yield / theoretical yield x 100%

gives the final answer. Note that the actual yield is 4.2g.
0
1 year ago
#4
(Original post by lane_in_pain)
Nope, that's not what I'm getting. Can you show your working? [Also thanks xD]
0
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