If a student needs to prepare 50g of bromobenzene and expects no more than a 75% yieldl, how much benzene should the student begin with if the yield is 75%?
C6H6(l)+ Br2(l) --> C6H5Br(l)+ HBr(g)
I calculated the moles of C6H5Br as .3185. But ion the end my answer is 18.7g
However, the correct answer is 33.2g. Which you get from using the mm of Br2 instead of C6H6.
Since i'm being asked about benzene would you use the mm of benzene?
You multiplied moles bromobenzene by 0.75. You should have divided by 0.75 to get 33.2%
To calculate how much benzene the student should begin with, we can use stoichiometry and the concept of percent yield.
First, let's calculate the theoretical yield of bromobenzene (C6H5Br) using the given information. We have 50g of bromobenzene, and the student expects no more than a 75% yield. So, the theoretical yield can be calculated as:
Theoretical Yield = 50g / 0.75 = 66.67g (rounded to two decimal places)
Now, let's calculate the number of moles of bromobenzene using its molar mass:
Molar mass of C6H5Br = 12.01g/mol (C) + 1.01g/mol (H) + 79.90g/mol (Br)
= 93.92g/mol
Moles of C6H5Br = 66.67g / 93.92g/mol
≈ 0.709mol (rounded to three decimal places)
According to the balanced chemical equation, the molar ratio between bromobenzene and benzene is 1:1. Therefore, the moles of benzene required will be the same as the moles of bromobenzene.
Moles of C6H6 = 0.709mol
Now, to find the mass of benzene required, we can multiply the moles of benzene by its molar mass:
Molar mass of C6H6 = 12.01g/mol (C) + 1.01g/mol (H) x 6
= 78.11g/mol
Mass of C6H6 = 0.709mol x 78.11g/mol
≈ 55.35g (rounded to two decimal places)
So, the correct answer is that the student should begin with approximately 55.35g of benzene.
It seems like there is a discrepancy between your calculation and the correct answer given. However, based on the balanced chemical equation, we need to consider the stoichiometry factors and the molar masses of the compounds involved. In this case, although we are ultimately interested in benzene, we need to use the molar mass of bromine (Br2) to calculate the moles accurately.