Deus te Amat Posted September 15, 2007 Share Posted September 15, 2007 (edited) I think I did something wrong in figuring out the math... the question is as follows... DDT, an insecticide harmful to fish, birds, and humans, is produced by the following reaction: [size=3]2C6H5Cl + C2HOCl3 --> C14H9Cl5 + H2O[/size] [size=1](chlorobenzene) (chloral) (DDT)[/size] In a government lab, 1142g of chlorbenzene is reacted with 485g of chloral. a) What mass of DDT is formed? b) Which reactant is limiting? Which is in excess? c) What mass of the excess reactant is left over? d) If the actual yield of DDT is 200.0 g, what is the percent yield? My answers… a) I figured out how much DDT each would have formed… a. 1142g x (1mol/112.55g) x (1 mol/2mol) x (349.462g/1mol) = 1772.93g b. 485g x (1 mol/ 144.378) x (1 mol/1mol) x (349.462g/1mol) = 1173.93g b) Therefore Chloral is the limiting and Chlorobenzene is in excess right? c) If Chlorobenzene is in excess, then to find how much left over you go… a. 1173.93g x (1 mol/ 349.462) x (2 mol/1 mol) x (112.55/1 mol) = 756.18g b. Is that right? 756.18g of excess? That doesn’t seem right now me… d) that really doenst make sense if I got 1173.93 g of DDT… ahhhhhh…. someone help... please? (the spacing isnt working.... sorry) DDT = C14H9Cl5) Edited September 15, 2007 by Deus_te_Amat Link to comment Share on other sites More sharing options...
CatholicCid Posted September 15, 2007 Share Posted September 15, 2007 (edited) Shouldn't b. 485g x (1 mol/ 144.378) x (1 mol/1mol) x (349.462g/1mol) = 1173.93g have a 2mol/1mol ratio, not a 1mol/1mol? -edit- Oh, that's 1 mol chloral to 1 mol ddt... so, nvm I'm going to run it through and see if I get anything different. Edited September 15, 2007 by CatholicCid Link to comment Share on other sites More sharing options...
Deus te Amat Posted September 15, 2007 Author Share Posted September 15, 2007 (edited) no... because the C2HOCl3 and the C14H9Cl5 dont have coefficients in front of them, therefore its 1/1 whereas C6H5Cl has a 2 as its coeffecient, making its mole ratio with DDT 2/1 edit- yep Edited September 15, 2007 by Deus_te_Amat Link to comment Share on other sites More sharing options...
CatholicCid Posted September 15, 2007 Share Posted September 15, 2007 (edited) Yeah, been about a year since I've done this stuff. My numbers are similiar to yours for a. I got 1798.29 g chlorbenzene and 1166.48 chloral. So yes, chloral is the limiting rxn and chlorbenzene is in excess. Now, I believe this is where you didn't do the question completely. For your B, your calculating how much of the non-limiting reactant actually did react with the limiting reactant. 756.18g is the amount that reacted, not the amount left over. To find the amount of excess reactant remaining, subtract the amount that reacted from the amount in the original sample. So, 1142 g chlorbenzene - 740.77 g = 401.22 g chlorbenzene left over. Note - I used my own numbers in any equations I did and I completely ignored any sig fig rules and used a Periodic Table that gives many decimal places, so our numbers won't match exactly. Edited September 15, 2007 by CatholicCid Link to comment Share on other sites More sharing options...
Deus te Amat Posted September 15, 2007 Author Share Posted September 15, 2007 Ohhhhhhhhhh... i was wondering if thatmight be perhaps what it was... Thank you!! yeah i was using the periodic table in my book. it was irritating me alot because i'm used to oxygen being 15.9994 but the book had 16 and Hydrogen being 1.00794 but the book 1.008... I really like the extended decimals more i wasn't doing sig figs either, but i probably should've been... but what about part D? Link to comment Share on other sites More sharing options...
Thy Geekdom Come Posted September 15, 2007 Share Posted September 15, 2007 The solution is much simpler: drop out of chemistry. It's what I did...and look where I am now! Link to comment Share on other sites More sharing options...
CatholicCid Posted September 15, 2007 Share Posted September 15, 2007 (edited) I believe percent yield is 100(actual mass of product/predicted mass of product) So 100(200 g DDT / 1166.48 g DDT) I got around 17%-ish Just wait until you get into rate laws... So much fun Edited September 15, 2007 by CatholicCid Link to comment Share on other sites More sharing options...
Deus te Amat Posted September 15, 2007 Author Share Posted September 15, 2007 urg!! that doesnt make sense though i mean, iknow thats the answer, and what i would have done... but it doestn make sense in relation to the question!! why would a government lab have such a low percent yeild!!! urg urg urg.... sometimes my logic gets in the way... thank you so much CatholiCid... i owe you one! Link to comment Share on other sites More sharing options...
CatholicCid Posted September 15, 2007 Share Posted September 15, 2007 (edited) It's a government lab... That should answer the question itself In a theoretical and logical sense, the amount of energy to cause the reaction would probably be the reason for such a low yield And your welcome... As someone who has suffered through such chemistry, i feel one should always try to make it less painful for others Edited September 15, 2007 by CatholicCid Link to comment Share on other sites More sharing options...
1337 k4th0l1x0r Posted September 16, 2007 Share Posted September 16, 2007 Am I the only one who caught the environmentalist statement in the question? Americans have kept African nations from using DDT when it could easily solve their malaria problems. Many of the DDT studies were at best shady scientific work. Link to comment Share on other sites More sharing options...
Deus te Amat Posted September 16, 2007 Author Share Posted September 16, 2007 Have you seen the Bald Eagle statistics lately? from a state that was effected by DDT usage, i can attest for its harmfulness... comparing the number of bald eagles from ages ago til now. DDT would help their malaria problem, but it would harm them in other ways, in their food supplies for one. DDT is a poision. no matter what it is, a poison is harmful Link to comment Share on other sites More sharing options...
curtins Posted September 16, 2007 Share Posted September 16, 2007 id help, but we're still on basic atomic structure and the like Link to comment Share on other sites More sharing options...
Deus te Amat Posted September 16, 2007 Author Share Posted September 16, 2007 ahhhh... Gen Chem lucky dog Link to comment Share on other sites More sharing options...
CatholicCid Posted September 16, 2007 Share Posted September 16, 2007 Just wait till organic pops out of nowhere. Link to comment Share on other sites More sharing options...
ardillacid Posted September 16, 2007 Share Posted September 16, 2007 I would help out, but it looks like the other cid has you covered. One piece of advice, watch your significant figures. You are blatantly ignoring them. It may seem like a pain, but learn it now, so later in your career it becomes second nature Link to comment Share on other sites More sharing options...
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