Edexcel alevel chemistry unit 1 2018 question

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Ahlam.Ib
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#1
Methane reacts with chlorine in the presence of UV radiation to produce chloromethane :
CH4 + Cl2 -> CH3Cl + HCl
Mr (methane=16 chlorine=17 chloromethane=50.5 hydrogen chloride=36.5)
When 3.20g of methane reacted with excess chlorine, 5.05g of chloromethane was made. What was the percentage yield?
A) 10%
B) 20%
C) 50%
D) 63%
Answer is C
Can someone explain it
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Chi chi5
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How do you calculate percentage yield? How do you calculate how much chloromethane you should have created in the end? Have you made any attempts at this question so far? Please show what you have, where exactly you are stuck
Last edited by Chi chi5; 5 months ago
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R_A_A
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(Original post by Ahlam.Ib)
Methane reacts with chlorine in the presence of UV radiation to produce chloromethane :
CH4 + Cl2 -> CH3Cl + HCl
Mr (methane=16 chlorine=17 chloromethane=50.5 hydrogen chloride=36.5)
When 3.20g of methane reacted with excess chlorine, 5.05g of chloromethane was made. What was the percentage yield?
A) 10%
B) 20%
C) 50%
D) 63%
Answer is C
Can someone explain it
yehh i got c
so use the equation actual yield moles/theoretical yield moles x100
so u find the moles of ch4 which is 0.2 mol by doing 3.2/16
then find out moles of ch3cl which is 0.1
then u knw its a 1:1 ratio between ch4 and ch3cl
do 0.1/0.2 x100
and u get 50%
remember actual yield is always smaller than theoretical if u get confused
as theoretical is the MAXIMUM amount of yield u could possibly obtain in a reaction

hope that helps
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Chi chi5
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(Original post by R_A_A)
yehh i got c
so use the equation actual yield moles/theoretical yield moles x100
so u find the moles of ch4 which is 0.2 mol by doing 3.2/16
then find out moles of ch3cl which is 0.1
then u knw its a 1:1 ratio between ch4 and ch3cl
do 0.1/0.2 x100
and u get 50%
remember actual yield is always smaller than theoretical if u get confused
as theoretical is the MAXIMUM amount of yield u could possibly obtain in a reaction

hope that helps
Reminder not to give the answers. It is better to help them figure it out on their own.
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Ahlam.Ib
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(Original post by Chi chi5)
How do you calculate percentage yield? How do you calculate how much chloromethane you should have created in the end? Have you made any attempts at this question so far? Please show what you have, where exact you are stuck
What i did was divide the molar mass of ch3cl by the mass of ch3cl multiplied by 100 and i got 10% which is wrong
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Ahlam.Ib
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#6
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(Original post by R_A_A)
yehh i got c
so use the equation actual yield moles/theoretical yield moles x100
so u find the moles of ch4 which is 0.2 mol by doing 3.2/16
then find out moles of ch3cl which is 0.1
then u knw its a 1:1 ratio between ch4 and ch3cl
do 0.1/0.2 x100
and u get 50%
remember actual yield is always smaller than theoretical if u get confused
as theoretical is the MAXIMUM amount of yield u could possibly obtain in a reaction

hope that helps
Why did u divide the moles aren’t we supposed to divide the masses when calculating the yield?
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Chi chi5
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(Original post by Ahlam.Ib)
What i did was divide the molar mass of ch3cl by the mass of ch3cl multiplied by 100 and i got 10% which is wrong
Think about the units. Molar mass is g/mol. Mass is g so what you’ve done leaves you with mol^-1 not moles.

Ok correcting that, you get mass/molar mass which gives you the amount of moles of methane.

Figure out the mol to mol ratio of ch4 and ch3cl. Once you’ve done that use the theoretical mols of ch3cl to figure out the theoretical mass. Then you have theoretical mass and actual mass. Use the formula for percentage yield to complete the problem.
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