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last SG · 2015-08-19T22:54:00+00:00

Topic : atomic radius Hi! This is from singapore cambridge nov a level exam year 2010,Paper 1 qn 1Qn: which element has the largest atomic radius?BrKKrScSo...

Flying grenade SG

Identify the hybridization of the imine N atom, and the orbital that the lone pair resides in, and you'll have your answer. If you still don't understand, go ask your school teacher or private tutor.

lone pair on N atom of tryptophan resides in a unhybridised p orbital. the lone pair of e- is extensively delocalised by resonance to the benzene ring to the right, as well as to the alkene to the left. it is also not nucleophilic due to the steric hindrance brought upon by benzene ring.

Flying grenade SG

Hi Ultima, hope u can help out here,

my answers for TPJC 2015 P1 is

1. B

2. C

3. C

4. C

5. C

6. A

7. C

8. D

9. B

10. C

11. C

12. D

13. C

14. C

15. B

16. C

17. A

18. C

19. D

20. D

21. C

22. A

23. B

24. C

25. A

26. C

27. A

28. B

29. C

30. C

31. D

32. D

33. A

34. A

35. C

36. C

37. C

38. D

39. D

40. D

hope u could help check and post the solns. Thank you !

UltimaOnline SG

Hi Ultima, hope u can help out here,

my answers for TPJC 2015 P1 is

1. B

2. C

3. C

4. C

5. C

6. A

7. C

8. D

9. B

10. C

11. C

12. D

13. C

14. C

15. B

16. C

17. A

18. C

19. D

20. D

21. C

22. A

23. B

24. C

25. A

26. C

27. A

28. B

29. C

30. C

31. D

32. D

33. A

34. A

35. C

36. C

37. C

38. D

39. D

40. D

hope u could help check and post the solns. Thank you !

1 B --- 11 D --- 21 A --- 31 D
2 C --- 12 D --- 22 A --- 32 B
3 C --- 13 B --- 23 C --- 33 D
4 C --- 14 C --- 24 D --- 34 B
5 C --- 15 D --- 25 D --- 35 B
6 A --- 16 C --- 26 D --- 36 D
7 C --- 17 A --- 27 A --- 37 B
8 D --- 18 A --- 28 B --- 38 A
9 B --- 19 B --- 29 C --- 39 D
10 B --- 20 C --- 30 A --- 40 D

Flying grenade SG

did and constructed the equation for disproportionation of Cl2 in hot aq.NaOH in a test, instead of memorising

i wrote Cl2 + 6OH- -> Cl- + ClO3- + 3H2O (completely balanced)

Cstoh's book (and other sources)

3Cl2 + 6OH- -> 5Cl- + ClO3- + H2O

is my eqn wrong? ? it's balanced correctly !!

notice the possibility of varying the stoichiometric coefficients of Cl2 and Cl- ?

e.g.

1 , 1

2, 3

3, 5

4, 7

UltimaOnline SG

did and constructed the equation for disproportionation of Cl2 in hot aq.NaOH in a test, instead of memorising

i wrote Cl2 + 6OH- -> Cl- + ClO3- + 3H2O (completely balanced)

Cstoh's book (and other sources)

3Cl2 + 6OH- -> 5Cl- + ClO3- + H2O

is my eqn wrong? ? it's balanced correctly !!

notice the possibility of varying the stoichiometric coefficients of Cl2 and Cl- ?

e.g.

1 , 1

2, 3

3, 5

4, 7

You really can't figure out why you're wrong, and need me to point it out to you??? Seriously???

Flying grenade SG

3Cl2 + 6OH- -> 5Cl- + ClO3- + H2O

is the correct equation because the charges on both side of equation is the same, and hence same number of Counter ions (Na+) is the same for both side of eqn.

UltimaOnline SG

3Cl2 + 6OH- -> 5Cl- + ClO3- + H2O

is the correct equation because the charges on both side of equation is the same, and hence same number of Counter ions (Na+) is the same for both side of eqn.

Ok, here's a BedokFunland JC challenge for you, solve it now on the forum to see if you've learnt something from what you've been discussing :

Write the ionic equation for the reaction between Cu2+ ions and potassium iodide solution, to generate copper(I) iodide precipitate and molecular iodine.

Flying grenade SG

2Cu2+(aq) + 4I-(aq) -> 2CuI(s) + I2(aq)

I2 (aq) state, not solid state.

UltimaOnline SG

is it

2Cu2+(aq) + 4I-(aq) -> 2CuI(s) + I2(s) ??

Almost entirely correct, except I2 should be aqueous, not solid. Write the equation (ideally draw out the mechanism) to explain why I2(s) is soluble in KI(aq).

Separate Qn : Write the balanced equation for the complete combustion of CxHyOH.

Flying grenade SG

oh yes !!!

iodine dissolves in aqueous KI solution , due to the formation of I3-(aq) ions. for full detailed explanation, shld draw mechanism.

Flying grenade SG

is it

CxHyOH + [x + (y+1)/4 -1] O2 -> xCO2 + (y+1)/2 H2O ?

UltimaOnline SG

is it

CxHyOH + [x + (y+1)/4 -1] O2 -> xCO2 + (y+1)/2 H2O ?

Almost correct, but your coefficient of O2 is slightly off. Here's the correct working to get the correct coefficient of O2.

Qn : Write the balanced equation for the complete combustion of CxHyOH.

2k + 1 = 2x + (y+1)/2
2k = 2x + (y+1)/2 - 1
k = (x + (y+1)/4 - 1/2)

Flying grenade SG

ahh okay i see, Thanks Ultima !!!!

Flying grenade SG

page 301 cs toh advanced guide, btm of page

should the arrows reach the H atom?

UltimaOnline SG

page 301 cs toh advanced guide, btm of page

should the arrows reach the H atom?

Yes.

Flying grenade SG

page 309 , btm of page

is there any special name for R+ ion ?

alkylium ion? haha

there is such thing as alkylium ion

https://en.m.wikipedia.org/wiki/Carbenium_ion

Flying grenade SG

cool name lmao

https://en.m.wikipedia.org/wiki/Magic_acid

UltimaOnline SG

page 309 , btm of page

is there any special name for R+ ion ?

alkylium ion? haha

Carbocation. When the C atom is part of the acyl group, then it's called the acylium ion (because the unipositive formal charge isn't stuck on C, it's delocalized by resonance over both the C and O atoms, try drawing both resonance contributors and thus the resonance hybrid).

UltimaOnline SG

cool name lmao

https://en.m.wikipedia.org/wiki/Magic_acid

Don't just see something unusual only, then just copy and paste the link with a "cool name lmao". Learn whatever you can from it.

For instance, try drawing out the full curved-arrow electron-flow mechanism (for both forward and backward reactions) using full displayed structural formula for the following equilibria.

Flying grenade SG

U.O. SUPER ZAI !!!!!

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