# Chem Multiple choice % yield Q!

(All 1:1 in formula)
In a preparation, with an excess of benzene, the mass of ethanoyl chloride (Mr = 78.5) used was 5.7 × 10−2 kg.
[1 mark]
The percentage yield of phenylethanone was 62%.
What mass, in grams, of phenylethanone was produced?
A 35g B 54g C 87g D 102g
[1 mark]
I got A buy apparently it’s B? Any help appreciated
Original post by uhhhh6678987654
(All 1:1 in formula)
In a preparation, with an excess of benzene, the mass of ethanoyl chloride (Mr = 78.5) used was 5.7 × 10−2 kg.
[1 mark]
The percentage yield of phenylethanone was 62%.
What mass, in grams, of phenylethanone was produced?
A 35g B 54g C 87g D 102g
[1 mark]
I got A buy apparently it’s B? Any help appreciated

Work out number of moles of ethanoyl chloride.
1:1 ratio
You got a number of moles of phenylethanone. Now use the Mr of phenylethanone to work out the maximum mass yield of it. I got around 87g.

Then you do 87 x 0.62 OR 87 x 62/100
Then you get 54g which is B

Edit: I suggest drawing the structure of phenylethanone if it was the Mr that got you.
(edited 1 year ago)
Original post by JA03
Work out number of moles of ethanoyl chloride.
1:1 ratio
You got a number of moles of phenylethanone. Now use the Mr of phenylethanone to work out the maximum mass yield of it. I got around 87g.

Then you do 87 x 0.62 OR 87 x 62/100
Then you get 54g which is B

Edit: I suggest drawing the structure of phenylethanone if it was the Mr that got you.

Hi,

So are we expected to know the Mr of phenylethanone? (Or at least know how to work it out from the skeletal formula?)
Original post by subbhy
Hi,

So are we expected to know the Mr of phenylethanone? (Or at least know how to work it out from the skeletal formula?)

You need to know how to work it out.
Given it is the product of the reaction described in the question (benzene + ethanoyl chloride, reacting in a 1:1 mole ratio and presumably in the presence of AlCl3), if you know your organic reactions, you should be able to work out the skeletal formula and hence it’s molecular formula and Mr.
Original post by TypicalNerd
You need to know how to work it out.
Given it is the product of the reaction described in the question (benzene + ethanoyl chloride, reacting in a 1:1 mole ratio and presumably in the presence of AlCl3), if you know your organic reactions, you should be able to work out the skeletal formula and hence it’s molecular formula and Mr.

The skeletal formula was given in the reaction but I’ve not yet been taught how to do what you mentioned. Good to know so thanks!
Original post by subbhy
Hi,

So are we expected to know the Mr of phenylethanone? (Or at least know how to work it out from the skeletal formula?)

YoU would be expected to know the structure of it so you would be able to get the Mr from that.