username5058598
Badges: 14
Rep:
?
#1
Report Thread starter 9 months ago
#1
1,2–dichloroethane undergoes thermal cracking to give chloroethene.

CH2ClCH2Cl ——> CH2=CHCl + HCl

Calculate the percentage yield of this process if 10.0 tonnes of the 1,2–dichloroethane yield 2.0 tonnes of chloroethene.


I worked this out and I got 40% but the correct answer is apparently 31.7% and I don’t understand why (they didn’t show working out). Can anyone please explain??
0
reply
Thiexp53
Badges: 9
Rep:
?
#2
Report 9 months ago
#2
Start off by working out the number of moles of 1,2-dichloroethane that decomposes. Moles (mol) = mass (g) / Mr so the moles will be 10,000,000/99 which is 101,010.101 moles.

From the equation we can see that one mole of 1,2-dichloroethane produces one mole of chloroethene, so there will also be 101,010.101 moles of chloroethene. We can use the equation again to work out the mass of chloroethene this should have produced: 101010.101 x 62.5 = 6,313,131.313 g or 6.313 tonnes.

Then divide the actual mass produced by the theoretical mass produced and multiply by 100 to get the percentage yield: (2 / 6.313) x 100 = 31.7%. Hope this helps .
2
reply
username5058598
Badges: 14
Rep:
?
#3
Report Thread starter 9 months ago
#3
(Original post by Thiexp53)
Start off by working out the number of moles of 1,2-dichloroethane that decomposes. Moles (mol) = mass (g) / Mr so the moles will be 10,000,000/99 which is 101,010.101 moles.

From the equation we can see that one mole of 1,2-dichloroethane produces one mole of chloroethene, so there will also be 101,010.101 moles of chloroethene. We can use the equation again to work out the mass of chloroethene this should have produced: 101010.101 x 62.5 = 6,313,131.313 g or 6.313 tonnes.

Then divide the actual mass produced by the theoretical mass produced and multiply by 100 to get the percentage yield: (2 / 6.313) x 100 = 31.7%. Hope this helps .
Thank you so much for your help! It all makes sense now

I’m also struggling with the next question.

Use the percentage yield and atom economy of this reaction to calculate how much in tonnes of the 1,2–dichloroethane is actually converted into chloroethene.

Any help would be appreciated
1
reply
Thiexp53
Badges: 9
Rep:
?
#4
Report 9 months ago
#4
Percentage yield we know from the previous question (31.7%). Atom economy we calculate by dividing the Mr of the desired product by the Mr of all reactants and multiplying by 100, in this case it would be (62.5 / 99) x 100 which equals 63.1%.

Then to work out how much of the 1,2-dichloroethane turns to chloroethene we multiply the mass of 1,2-dichloroethane, the percentage atom economy and the percentage yield together: 0.317 x 0.631 x 10 = 2.00126 tonnes (or just 2.00 tonnes to 3 s.f.).
0
reply
username5058598
Badges: 14
Rep:
?
#5
Report Thread starter 9 months ago
#5
(Original post by Thiexp53)
Percentage yield we know from the previous question (31.7%). Atom economy we calculate by dividing the Mr of the desired product by the Mr of all reactants and multiplying by 100, in this case it would be (62.5 / 99) x 100 which equals 63.1%.

Then to work out how much of the 1,2-dichloroethane turns to chloroethene we multiply the mass of 1,2-dichloroethane, the percentage atom economy and the percentage yield together: 0.317 x 0.631 x 10 = 2.00126 tonnes (or just 2.00 tonnes to 3 s.f.).
Thank you so much!
0
reply
jayjayfucopil
Badges: 10
Rep:
?
#6
Report 9 months ago
#6
(Original post by Thiexp53)
Start off by working out the number of moles of 1,2-dichloroethane that decomposes. Moles (mol) = mass (g) / Mr so the moles will be 10,000,000/99 which is 101,010.101 moles.

From the equation we can see that one mole of 1,2-dichloroethane produces one mole of chloroethene, so there will also be 101,010.101 moles of chloroethene. We can use the equation again to work out the mass of chloroethene this should have produced: 101010.101 x 62.5 = 6,313,131.313 g or 6.313 tonnes.

Then divide the actual mass produced by the theoretical mass produced and multiply by 100 to get the percentage yield: (2 / 6.313) x 100 = 31.7%. Hope this helps .
(Original post by Thiexp53)
Percentage yield we know from the previous question (31.7%). Atom economy we calculate by dividing the Mr of the desired product by the Mr of all reactants and multiplying by 100, in this case it would be (62.5 / 99) x 100 which equals 63.1%.

Then to work out how much of the 1,2-dichloroethane turns to chloroethene we multiply the mass of 1,2-dichloroethane, the percentage atom economy and the percentage yield together: 0.317 x 0.631 x 10 = 2.00126 tonnes (or just 2.00 tonnes to 3 s.f.).
Nice!
0
reply
X

Quick Reply

Attached files
Write a reply...
Reply
new posts
Back
to top
Latest
My Feed

See more of what you like on
The Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

Personalise

Current uni students - are you thinking of dropping out of university?

Yes, I'm seriously considering dropping out (85)
14.24%
I'm not sure (27)
4.52%
No, I'm going to stick it out for now (189)
31.66%
I have already dropped out (12)
2.01%
I'm not a current university student (284)
47.57%

Watched Threads

View All
Latest
My Feed