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• supercat

  8 Oct 16, 16:11

  Originally posted by UltimaOnline:

  
  

  Haha thank you :)

• Flying grenade

  8 Oct 16, 18:11

  https://www.dropbox.com/s/zn8qpqilck3wbvz/20161008_180749-1.jpg?dl=0

  NJC 2013 p3 qn 4eiv

  Weak base strong acid titration CO32- + HCl

  for the calculation of pH when excess HCl is used, do we need to consider common ion effect, where high [H+] from HCl suppresses dissociation of H2CO3

   

  if i consider ntotal from HCl only, i calculate pH = 2.07

  if i consider HCl+ 1molH+ from H2CO3 , pH = 1.60

  if i consider HCl + 2molH+ from H2CO3 , pH= 1.38

• UltimaOnline

  8 Oct 16, 18:52

  Originally posted by Flying grenade:

  https://www.dropbox.com/s/zn8qpqilck3wbvz/20161008_180749-1.jpg?dl=0

  NJC 2013 p3 qn 4eiv

  Weak base strong acid titration CO32- + HCl

  for the calculation of pH when excess HCl is used, do we need to consider common ion effect, where high [H+] from HCl suppresses dissociation of H2CO3

   

  if i consider ntotal from HCl only, i calculate pH = 2.07

  if i consider HCl+ 1molH+ from H2CO3 , pH = 1.60

  if i consider HCl + 2molH+ from H2CO3 , pH= 1.38

  
  Yes, you need to consider common ion effect. In excess HCl, pH is determined by the strongest acid HCl, all the CO3 2- will be protonated and eliminated from solution in the form of CO2.
• Flying grenade

  8 Oct 16, 18:52

  https://www.dropbox.com/s/yvz3cotvl3r2gt4/20161008_184906-1.jpg?dl=0

  https://www.dropbox.com/s/otc8gwvqu6dh0wn/20161008_184909-1.jpg?dl=0

  how to distinguish isomer W and X?

  why the answer say white solid? phenylamine is colorless-yellow liquid, sodium ethanoate is soluble in water

• Flying grenade

  8 Oct 16, 18:54

  Originally posted by UltimaOnline:

  
  Yes, you need to consider common ion effect. In excess HCl, pH is determined by the strongest acid HCl, all the CO3 2- will be protonated and eliminated from solution in the form of CO2.

  ohh okay wow i see!! 

  dk why answer write pH= 1.30 though

• Flying grenade

  8 Oct 16, 19:00

  Originally posted by UltimaOnline:

  
  Yes, you need to consider common ion effect. In excess HCl, pH is determined by the strongest acid HCl, all the CO3 2- will be protonated and eliminated from solution in the form of CO2.

  for this qn, conc hcl given is 0.05 M, so i calculate using nHCl = 0.05 ×10/1000

  nH+ = nHCl

  total vol = 50 + 10 = 60cm3

  [H+] = 1/120 

  pH = -lg [H+] = 2.08 (3sf)

• UltimaOnline

  8 Oct 16, 22:06

  Originally posted by Flying grenade:

  https://www.dropbox.com/s/yvz3cotvl3r2gt4/20161008_184906-1.jpg?dl=0

  https://www.dropbox.com/s/otc8gwvqu6dh0wn/20161008_184909-1.jpg?dl=0

  how to distinguish isomer W and X?

  why the answer say white solid? phenylamine is colorless-yellow liquid, sodium ethanoate is soluble in water

  
  Alkaline hydrolysis, followed by iodoform test, is a better answer.

  You keep making the same type of mindless (ie. lacking mindfulness or situational awareness) mistakes over and over again, you coconaden. Do you really expect to see a "colorless to yellow liquid" under these conditions?

• UltimaOnline

  8 Oct 16, 22:13

  Originally posted by Flying grenade:

  for this qn, conc hcl given is 0.05 M, so i calculate using nHCl = 0.05 ×10/1000

  nH+ = nHCl

  total vol = 50 + 10 = 60cm3

  [H+] = 1/120 

  pH = -lg [H+] = 2.08 (3sf)

  
  My bad, your pH is correct.
• Flying grenade

  8 Oct 16, 22:19

  Originally posted by UltimaOnline:

  
  Alkaline hydrolysis, followed by iodoform test, is a better answer.

  You keep making the same type of mindless (ie. lacking mindfulness or situational awareness) mistakes over and over again, you coconaden. Do you really expect to see a "colorless to yellow liquid" under these conditions?

  cannot, thats why idk how distinguish 

   

  what was the white ppt the answer key was referring to uh???

• Flying grenade

  8 Oct 16, 22:21

  Originally posted by UltimaOnline:

  
  U damn coconaden. Simple qn like this also make mistake. U wrong lah, not NJC teacher wrong. Figure out ur own mistake.

  tell me la pls faster

• Flying grenade

  8 Oct 16, 23:31

  https://www.dropbox.com/s/q9cjxra10mbj18y/20161008_233029.jpg?dl=0

  what kind of molecule is V ?

• UltimaOnline

  9 Oct 16, 00:26

  Originally posted by Flying grenade:

  https://www.dropbox.com/s/q9cjxra10mbj18y/20161008_233029.jpg?dl=0

  what kind of molecule is V ?

  
  The reagents are in error. Sodium nitrite, not sodium nitrate, should be used.

  Protonating O=N--O- generates O=N--O-H, which can be further protonated into O=N--OH2+ which can decompose into H2O and O=N+, an electrophile to be attacked by the amine (ie. electrophilic substitution) generate the final product of N,N-dimethylnitrosamine.

• UltimaOnline

  9 Oct 16, 00:53

  Originally posted by Flying grenade:

  what was the white ppt the answer key was referring to uh???

  
  Phenylamine
• UltimaOnline

  9 Oct 16, 00:53

  Originally posted by Flying grenade:

  for this qn, conc hcl given is 0.05 M, so i calculate using nHCl = 0.05 ×10/1000

  nH+ = nHCl

  total vol = 50 + 10 = 60cm3

  [H+] = 1/120 

  pH = -lg [H+] = 2.08 (3sf)

  
  My bad, your pH is correct.
• Flying grenade

  9 Oct 16, 00:54

  Originally posted by UltimaOnline:

  
  The reagents are in error. Sodium nitrite, not sodium nitrate, should be used.

  Protonating O=N--O- generates O=N--O-H, which can be further protonated into O=N--OH2+ which can decompose into H2O and O=N+, an electrophile to be attacked by the amine (ie. electrophilic substitution) generate the final product of N,N-dimethylnitrosamine.

  u godly sia. u pwn everyone 

  u should write a godlike chem textbook 

• Flying grenade

  9 Oct 16, 00:54

  Originally posted by UltimaOnline:

  
  Phenylamine

  phenylamine not a white solid right?

• Flying grenade

  9 Oct 16, 00:55

  Originally posted by UltimaOnline:

  
  My bad, your pH is correct.

  excess 10cm3 no meh??

   

  help pls

• Flying grenade

  9 Oct 16, 00:56

  or be godlike proof-reader /vetter

   

  chem god

• UltimaOnline

  9 Oct 16, 00:57

  Originally posted by Flying grenade:

  phenylamine not a white solid right?

  
  Is phenylamine a white ppt or a yellow liquid? Depends on whether ... ... ... ... (go figure out urself, u coconaden).
• Flying grenade

  9 Oct 16, 01:01

  Originally posted by UltimaOnline:

  Is phenylamine a white ppt or a yellow liquid? Depends on whether ... ... ... ... (go figure out urself, u coconaden).

  all 21 Singapore JCs are great 

• Flying grenade

  9 Oct 16, 01:02

  Originally posted by UltimaOnline:

  
  Is YJC a good JC or a lousy JC? Depends on whether you're comparing it with MI or RJC.

  Is phenylamine a white solid or a yellow liquid? Depends on whether ... ... ... ... (go figure out urself, u coconaden).

  eh that soln/molecule/solid

  both W and X amide both solid , pour colorless naoh in?? idk sia

  help me 

  cocoboss/cocolover eat cocokrunch,drink coconut juice

• Flying grenade

  9 Oct 16, 01:04

  where my vol of HCl wrong? 

   

  rescue me pls

• UltimaOnline

  9 Oct 16, 01:04

  Originally posted by Flying grenade:

  where my vol of HCl wrong? 

   

  rescue me pls

  
  My bad, your pH is correct.
• UltimaOnline

  9 Oct 16, 01:05

  Originally posted by Flying grenade:

  eh that soln/molecule/solid

  both W and X amide both solid , pour colorless naoh in?? idk sia

  help me cocoboss

  
  Figure it out yourself. Think step by step what happens in the series of reactions.
• Flying grenade

  9 Oct 16, 01:06

  Originally posted by UltimaOnline:

  
  My bad, your pH is correct.

  so i pwn the NJC cher for that qn