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## anonymous one year ago Question 34

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1. anonymous

2. anonymous

@aaronq

3. Disco619

Is there an Answer key from which the answer can be confirmed?

4. anonymous

in an organic synthesis 60% yield of product is achieved. which of these conversions are consistent with this information 1) 74 g of butan-2-ol -> 44.64 g of butanone 2)74 g of butan-1-ol -> 54.56 g of butanoic acid 3) 74 g of 2-methylpropane-1-ol -> 54.56 g of 2-methylpropanoic acid

5. anonymous

Another question ^

6. Disco619

According to me, the answer is 2. After 2 minutes, the sulfuric acid has produced more gas than ethanoic acid.

7. anonymous

Yes for 34 all are correct

8. Disco619

Ok so we can choose more than 1 option?

9. Disco619

The answer is 1. 74 g of butan-2-ol -> 44.64 g of butanone

10. anonymous

Yeah the options are A. 1, 2 and 3 B. 1 and 2 C. 2 and 3 D. 1 only

11. Disco619

Oh okay, then it's A.

12. anonymous

Same goes for the second question A all three are correct

13. Disco619

Sulfuric Acid is a stronger acid than Ethanoic Acid which is a weak acid. A Strong Acid fully dissociates Hydrogen ions in a solution, a weak Acid partially dissociates (gives out Hydrogen ions). More dissociation of Hydrogen ions would mean more amount of gas (hydrogen gas) released in the reaction, and the faster it would be released as the concentration of Hydrogen ions is greater.

14. Disco619

I wouldn't know about the second question cause that's the first time i'm facing that kind of a situation in Chemistry. Hopefully you understood the first Question's answer!

15. Disco619

Sulfuric Acid would also be at a higher temperature because, both reactions being exothermic (release heat, i.e heat 'exit'), the Stronger Acid would be more hotter as the energy/heat released in bond formation would be greater as Greater number of bonds are being made, as it's concentration is greater.

16. anonymous

Oh alright

17. anonymous

But Sulphuric acid's concentration is same as ethanoic acid.

18. Disco619

Yes, the MOLECULES concentration is same. But the amount of Hydrogen ions Sulfuric Acid 'donates' to the solution is Greater than Ethanoic Acid. Sulfuric Acid donates almost ALL of it's Hydrogen ions, whereas Ethanoic acid donates partially.

19. anonymous

Ohhhh i got it now

20. anonymous

So how about second question?

21. Disco619

For example. The Circles represent the 'MOLECULES' of the acid, and the Circles with 'X' in them are the ones that 'donate' hydrogen ions. |dw:1433717182050:dw| Hope you got it now!

22. anonymous

Ahaha Nice nice i got it now thanks so much

23. Disco619

I don't really know about the Second question, I can't say because I just used this: $\frac{ 60 }{ 100 } \times 74 = 44. 4$ The good ol' math way, but if all are correct then I wouldn't know, this might have a Chemistry side to it.

24. Disco619

Maybe it's that it's not EXACTLY 60% yield, as NOTHING can be perfect in Science except Theoretically speaking. The Theoretical Yield must be 44.4g, but Experimental yield can differ by a little.

25. anonymous

I used the same method i got an A in olevels maths :v but alevel maths dissapointed me gave the exams recently not went good sigh.

26. Disco619

Hahaha Nice Nice! I JUST got done with my O'Levels. Gave the CIEs a week or two ago. I was very very very bad at Chemistry, I hated it, but I got to know this teacher and man (maybe you're a girl ahah), he made me fall in love with Chemistry in so little time. I'm still trying to perfect it.

27. Disco619

I've failed Maths since 6th grade lol, i'm really bad at it, you have no idea. But the CIEs went pretty good it's hard for even me to believe >.>

28. anonymous

Dua kero meray bhi achay ho jaen.

29. anonymous

I just freaked you out a little right??

30. Disco619

HAHAHAH OMFG XD iA iA Achay ho jayen ge, pellet DAMN! xD

31. Disco619

sh!t* :@

32. anonymous

Yeah Good morning.

33. Disco619

It's.. :| 4 AM, but yeh Good Morning! Goodluck though! If you need any more help (from an O'Level student lol) feel free to ask, i'll be on my way to help someone else!

34. anonymous

Azaan ho gae hae iss liey mein ne kaha

35. Disco619

Umm btw if you're in Lahore, try studying from Sir Mohammad Ali. That's the BEST Chemistry teacher you'll ever meet. EVER.

36. Disco619

Specially for A'Level students.

37. anonymous

No not in Lahore.

38. Disco619

Ok so I just realized the answer to Question 34 is 1 and 2.

39. anonymous

and 3. all three are correct

40. Disco619

No, not 3. I also thought 3 but I read the Question again. Only 1 and 2. If your Answer Key says all 3 are correct, i'd bet 9.9/10 that it's wrong.

41. anonymous

today's my exam i hope this doesn't come up :o. why cannot C be though?

42. Disco619

My Cousin's exam is today too, He's doing AS. I confirmed it from him. Lemme see if I can explain

43. Disco619

OK I forgot what that rule was named (after the scientist) which told us how to make the reactions go in forward direction (pressure, temperature, moles, concentration), if you remember, you can remind me.

44. Disco619

Ok I remember, it was Le Chatelier's principle.

45. anonymous

whats the problem in it? carboxylic acids are weak acids....

46. anonymous

that was easy it just slipped out of my mind

47. anonymous

so obviously h2so4 would give less yield

48. anonymous

Ann-Hybrid why its A in the markscheme then

49. Disco619

Anyways, the thing is. When the partially dissociated hydrogen ions in weak acid get used up and are released as Hydrogen gas, their concentration decreases in the solution, which causes the acid to release MORE Hydrogen ions. This keeps on happening till all the hydrogen ions are released from the acid and at the end, the gas would be the same amount as of Sulfuric acid, as their volume and concentration is same.

50. anonymous

Ann-Hybrid it's something you won't understand.

51. anonymous

rostella

52. Disco619

Get it?

53. anonymous

is common sense....that h2so4 would give more yeild at any point

54. anonymous

but ofcourse its Common sense

55. anonymous

Ann-Hybrid stop it now i'm trying to focus here

56. anonymous

kay...u focus..

57. Disco619

The difference is, the Sulfuric Acid reaction would be faster and more 'intense' (exothermic) as the frequency of fruitful collisions is greater due to it's concentration of Hydrogen Ions. At one time, GREATER Number of ions are released, whereas in the Organic Acid, it's weak and at one time, less number are being released and when they escape as Hydrogen gas, the decrease in concentration causes them to release more Hydrogen ions.

58. anonymous

I thought the same @Disco619 but just got confused when i saw the markscheme it sure is misleading

59. Disco619

You just have to trust yourself, I also had trouble cause Marking scheme does lower your confidence sometimes. Goodluck!

60. anonymous

no wait you said earlier that weak acid dissociates partially it won't give much OH ions so 3 can be correct in this way

61. Disco619

Not 'OH', 'H' ions.

62. anonymous

i get it i get it it will be used up by the end of reaction.

63. Disco619

Yes they DO Dissociate partially! But when the - whatever dissociated ions - in the solution escape (as H2 in this case), their concentration decreases, which causes the weak acid to dissociate MORE of it's ions. Then they get used up, more are released, they're used up and so on... Till the acid runs out of Hydrogen ions to be released (as the metal was in excess)

64. anonymous

oh yeah H ions

65. anonymous

ohh so markscheme is a lie. oh well.

66. Disco619

Yup!

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