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• Flying grenade

  2 Jun 16, 19:57

  Absence of formal charge or having a stable octet/duplet structure is more critical/important in molecular stabilities?

• UltimaOnline

  2 Jun 16, 20:13

  Originally posted by Flying grenade:

  Absence of formal charge or having a stable octet/duplet structure is more critical/important in molecular stabilities?

  
  Stable octet of course more important lah, hence the term "stable octet".
• Flying grenade

  2 Jun 16, 20:37

  Thanks !!!

• Flying grenade

  7 Jun 16, 20:59

  Is CO2 considered an organic compound?

  If not, why?

   

  Urea : CO(NH2)2 doesn't have a C-H or C-C bond, but is still considered organic 

  It is produced in the liver 

  CO2 can be produced from inorganic reactions

  CO2 is also produced in organic rxns e.g. photosynthesis, respiration 

  Urea, an organic compound, can be synthesised 

  Both are carbon containing covalent compounds 

• Flying grenade

  7 Jun 16, 21:00

  .

• UltimaOnline

  7 Jun 16, 21:45

  Because on another planet without life (ie. inorganic), naturally occurring carbon on the surface of the planet can still be combusted (by high temperatures on the planet) to generate CO2. Hence CO2 can exist even without living organisms, therefore CO2 is considered inorganic.

  And questions like these are not relevant to the syllabus, so (especially) in Oct and Nov, if you keep spamming questions like these, or worse, after I give a brief answer, if you still keep flogging the dead horse by OCD spamming "but why? but why?!?", I'll ignore you and not reply further.

• Flying grenade

  7 Jun 16, 22:16

  Thanks! !!!

• Flying grenade

  8 Jun 16, 13:40

  Page 248 K.S. Chan planning book

   Test for phenol

  Add aq NaOH . Observation : phenol dissolves, two layers become one

  What does this mean?

  Say we want to distinguish two organic liquids, both of them are colorless, in two different test tubes

  When we add aq NaOH to the one containing phenol,

  Is it that aq NaOH and phenol forms two distinct layers momentarily, seen from the difference in translucency, and then when phenol dissolves it becomes a homogeneous translucent soln?

   

  Same for RCOOH pg 249

• Flying grenade

  8 Jun 16, 14:01

  Page 249

  Ooh, Ethanal is the only Aldehyde that can undergo iodoform reaction?

• UltimaOnline

  8 Jun 16, 15:21

  Originally posted by Flying grenade:

  Page 249

  Ooh, Ethanal is the only Aldehyde that can undergo iodoform reaction?

  
  Yes.
• UltimaOnline

  8 Jun 16, 15:25

  Originally posted by Flying grenade:

  Page 248 K.S. Chan planning book

   Test for phenol

  Add aq NaOH . Observation : phenol dissolves, two layers become one

  What does this mean?

  Say we want to distinguish two organic liquids, both of them are colorless, in two different test tubes

  When we add aq NaOH to the one containing phenol,

  Is it that aq NaOH and phenol forms two distinct layers momentarily, seen from the difference in translucency, and then when phenol dissolves it becomes a homogeneous translucent soln?

   

  Same for RCOOH pg 249

  
  Not even momentarily. If NaOH(aq) is added drop by drop, the phenol layer dissolves bit by bit into the aqueous layer, as phenoxide is more soluble in water than ether. If excess NaOH(aq) is added immediately, the phenol layer completely dissolves into the aqueous layer immediately.
• Flying grenade

  8 Jun 16, 15:35

  OOOHH !!! THANKS ULTIMA !

• Flying grenade

  9 Jun 16, 22:34

  Difference between acidity and strength of acid?

  Acidity of soln (molarity of H+) and the tendency for a acid to deprotonate is it?

   

  Acids do not necessarily have COOH functional group

  https://www.dropbox.com/s/99fuo0hj966t1c3/20160609_223822.jpg?dl=0

  COOH functional group for carboxylic acid

• Flying grenade

  9 Jun 16, 22:46

  Water is an acid

• UltimaOnline

  9 Jun 16, 23:40

  Originally posted by Flying grenade:

  Difference between acidity and strength of acid?

  Acidity of soln (molarity of H+) and the tendency for a acid to deprotonate is it?

   

  Acids do not necessarily have COOH functional group

  https://www.dropbox.com/s/99fuo0hj966t1c3/20160609_223822.jpg?dl=0

  COOH functional group for carboxylic acid

  
  Measure of acidity (ie. pH) is referring to for solutions.

  Strength of an acid is measured by its Ka or pKa value.

  Proticity refers to how many moles of H+ one mole of the acid can donate, or how many moles of H+ one mole of base can accept.

  Obviously only those acids with the COOH group are called carboxylic acids. Obviously not all acids have that group. Why are you stating the obvious?

  Option D is the answer, because its conjugate base is most effectively stabilized (among the 4 options), by delocalizing the uninegative formal charge over 2 electronegative, electron-withdrawing O atoms (ie. similar acidic strength to carboxylic acids). You *have* to draw the mechanism for the resonance contributors to fully understand this.

• Flying grenade

  10 Jun 16, 00:00

  thanks oTL

• Flying grenade

  14 Jun 16, 17:21

  page 265 planning book

  want to isolate the filtrate 

  what does it mean by retain the filtrate and carry out the extraction process on the filtrate?

  isn't the filtrate alr seperated from the residue alr (in the conical flask/buchner flask alr)?

  what does it mean evaporate the filtrate to dryness using water bath, when it's the filtrate that we want???

  have something attached to the top to collect the filtrate gas?? or fractional distillation? 

• UltimaOnline

  14 Jun 16, 18:17

  Originally posted by Flying grenade:

  page 265 planning book

  want to isolate the filtrate 

  what does it mean by retain the filtrate and carry out the extraction process on the filtrate?

  isn't the filtrate alr seperated from the residue alr (in the conical flask/buchner flask alr)?

  what does it mean evaporate the filtrate to dryness using water bath, when it's the filtrate that we want???

  have something attached to the top to collect the filtrate gas?? or fractional distillation? 

  
  This is the sort of qn that u probably still wun understand after I type out a reply. So if u still dun get it after this, go ask ur school teacher or private tutor. Dun flog the dead horse.

  U misread the book : it says, if you don't want the species in the filtrate, then evaporate the filtrate to dryness, then take the residue. This will work if the filtrate is simple covalent rather than soluble ionic. If the filtrate is wanted, then retain (ie. don't throw away) the filtrate, and carry out various extraction processes on the filtrate (the exact extraction process depends on whether the species in the filtrate is soluble ionic or covalent molecular).

• Flying grenade

  14 Jun 16, 18:56

  OOOOOH THANKS ULTIMA !!!

• Flying grenade

  14 Jun 16, 19:14

  yeah lor, provided the solid residue is insoluble in the filtrate, just boil the filtrate off and collect the residue 

  wonder why ks chan wrote this in this manner, making it seem like boiling of the filtrate is a secondary technique

  shld be at the same primary level - the two techniques expounded in pg 264 and 265

• ArJoe

  17 Jun 16, 17:15

  Hi, for a level 2012 paper 2 question 2iii which asks why so2 and not so3 is formed, can i say it is because when heated, temperature increase, hence by lcp system attempts to decrease temperature by favouring reverse reaction?
• UltimaOnline

  17 Jun 16, 19:06

  Originally posted by ArJoe:

  Hi, for a level 2012 paper 2 question 2iii which asks why so2 and not so3 is formed, can i say it is because when heated, temperature increase, hence by lcp system attempts to decrease temperature by favouring reverse reaction?

  
  Not acceptable. Nice try though. The question specifies it is about S to SO2 versus S to SO3. This isn't about the equilibrium between SO2 and SO3. So the only acceptable answer is the most directly relevant one : ie. this is primarily a matter of kinetics, not equilibria.
• ArJoe

  18 Jun 16, 15:35

  Hi ultimaonline, thanks for your detailed response. For 2011 paper 2 question bii, i wrote atomic radius increases from c to si to ge, hence extent of orbital overlap decreases from cc bond to sisi bond to ge-ge bond, resulting in decreasing covalent bond strength hence less energy required to overcome. Is it acceptable? for 2011 paper 2 question 5, for the further relevant piece of information, for geometrical isomers i said that geometrical isomers have c c double bond to restrict free rotation of the molecule. There must also be 2 different atoms or group of atoms directly bonded to each c atom of the double bond. for optical isomerism, i said that if both enantiomers are not present in equal amounts, the compounds can rotate plane polarised light. For optical isomerism to arise, compound must have a chiral carbon atom, carbon bonded to 4 different atoms. Are my answers acceptable?
• UltimaOnline

  18 Jun 16, 16:25

  Originally posted by ArJoe:

  Hi ultimaonline, thanks for your detailed response.

  For 2011 paper 2 question bii, i wrote atomic radius increases from c to si to ge, hence extent of orbital overlap decreases from cc bond to sisi bond to ge-ge bond, resulting in decreasing covalent bond strength hence less energy required to overcome. Is it acceptable?

  for 2011 paper 2 question 5, for the further relevant piece of information, for geometrical isomers i said that geometrical isomers have c c double bond to restrict free rotation of the molecule. There must also be 2 different atoms or group of atoms directly bonded to each c atom of the double bond.
  for optical isomerism, i said that if both enantiomers are not present in equal amounts, the compounds can rotate plane polarised light. For optical isomerism to arise, compound must have a chiral carbon atom, carbon bonded to 4 different atoms.
  Are my answers acceptable?

  
  Yes ArJoe, your answers are acceptable.
• Flying grenade

  20 Jun 16, 20:29

  when the Eθcell of an overall cell reaction is +ve , do we say the reaction is thermodynamically/energetically favourable/feasible?