Originally posted by Ephemeral:What is a simple chemical test to differentiate between 2,4,6-tribromophenol and 2,4,6-trichlorophenylamine? (Cannot use FeCl3)
Vary the pH, and observe (with your eyes) which precipitate dissolves at which pH.
https://twitter.com/itsliyingg/status/717342018427420672
Qns 14 part (d)
https://twitter.com/itsliyingg/status/717347418149289984
Qns 15
Originally posted by Liying98:https://twitter.com/itsliyingg/status/717347418149289984
Qns 15
Originally posted by Liying98:https://twitter.com/itsliyingg/status/717342018427420672
Qns 14 part (d)
Is amine group more basic in alpha amino acid or beta/ gamma amino acid?
Originally posted by Ephemeral:Is amine group more basic in alpha amino acid or beta / gamma amino acid?
If you understood what I've just said, you will be able to figure out the answer to your question.
When compound C6H5OCOCH2CH3 is heated with NaOH (aq), why it results into Phenoxide ion and CH3CH2COO- instead of a phenol and CH3CH2COO-?
When compound C6H5NHCOCH2CH3 is heated with NaOH (aq), why it results into C6H5NH2 and CH3CH2COO- instead of a (C6H5NH-) (Na+) and CH3CH2COOH?
Originally posted by Mrworry:When compound C6H5OCOCH2CH3 is heated with NaOH (aq), why it results into Phenoxide ion and CH3CH2COO- instead of a phenol and CH3CH2COO-?
When compound C6H5NHCOCH2CH3 is heated with NaOH (aq), why it results into C6H5NH2 and CH3CH2COO- instead of a (C6H5NH-) (Na+) and CH3CH2COOH?
2nd qn : because carboxylic acid is far more acidic than phenylamine (which is in fact, far more basic than it is acidic ; to deprotonate phenylamine, you need an extremely strong base such as LDA, which is beyond the A level syllabus), and hence, OH- deprotonates carboxylic acid instead of phenylamine.
MrWorry, no offence, but from your questions, it's evident that your fundamentals (in what makes something acidic or basic) is severely lacking. If you're taking your A levels 6 months later this year in 2016, you might wish to engage private tuition asap.
#1 - You're expected to be aware that you have to use excess NaOH(aq), heat under reflux, to carry out hydrolysis or ester or amide groups. Since NaOH is in excess, deprotonation of acidic groups such as COOH or phenol will occur.
#2 - To *fully* understand the reaction (including the exact structure of the products, including protonation/deprotonation), you need to draw out (or at least view) the full curved-arrow electron-flow reaction mechanism. If your school teacher or private tutor don't want to teach you (I teach my BedokFunland JC students these mechanisms), google them out yourself.
Originally posted by UltimaOnline:
No one reading this can figure it out? Fine, BedokFunland JC to the rescue.Vary the pH, and observe (with your eyes) which precipitate dissolves at which pH.
Is there any way or a reaction that cl2 can displace the br positions?
Originally posted by UltimaOnline:
No one reading this can figure it out? Fine, BedokFunland JC to the rescue.Vary the pH, and observe (with your eyes) which precipitate dissolves at which pH.
Is it, 2,4,6 trichlorophenylamine will dissolve at a higher pH than 2,4,6 tribromophenol because phenylamine functional group is less acidic( more basic) than phenol functional group ?
Why will a compound dissolve in different pH than another compound? Is it because one compound is more or less basic than another cpd?
Is it a stronger bronsted lowry base will more readily accept proton as compared to a weaker bronsted lowry base,
Hence it'll dissolve at a higher pH(less concentration of H+) ,
compared to a weaker base which requires lower pH(higher concentration of H+) in order to accept the proton in order to dissolve, is it?
Originally posted by Flying grenade:Is there any way or a reaction that cl2 can displace the br positions?
Originally posted by Flying grenade:Is it, 2,4,6 trichlorophenylamine will dissolve at a higher pH than 2,4,6 tribromophenol because phenylamine functional group is less acidic( more basic) than phenol functional group ?
Originally posted by Flying grenade:Is it, 2,4,6 trichlorophenylamine will dissolve at a higher pH than 2,4,6 tribromophenol because phenylamine functional group is less acidic( more basic) than phenol functional group ?
Why will a compound dissolve in different pH than another compound? Is it because one compound is more or less basic than another cpd?
Is it a stronger bronsted lowry base will more readily accept proton as compared to a weaker bronsted lowry base,
Hence it'll dissolve at a higher pH(less concentration of H+) ,
compared to a weaker base which requires lower pH(higher concentration of H+) in order to accept the proton in order to dissolve, is it?
Originally posted by UltimaOnline:
No marks awarded in A levels for your answer. You have to draw out both phenol and phenylamine under acidic pH, and separately under alkaline pH, to understand the correct answer.
Sorry , Error in my post above, Phenylamine will dissolve at a lower pH, phenol will dissolve at a higher pH
Phenylamine protonates at acidic pH to form my phenylammonium ion,
Phenol deprotonates at basic pH to form phenoxide ion,
is it?
Originally posted by Flying grenade:Sorry , Error in my post above
Phenylamine protonates at acidic pH to form my phenylammonium ion,
Phenol deprotonates at basic pH to form phenoxide ion,
is it?
Several questions!
Inorganic Chem:
For transition metal complex right, how do you determine the coordination number. I understand that most of them are 6 but sometimes it can be 4 or 2, and i get stumped when i see the answer key. so how do i predict the coordination number?
Physical chem:
Do you mind explaining how do you predict solubility? isit as simple as polar solvents dissolve polar reagents and non polar dissolve non polar? refering to TYS 2009 P2 Q2(b) I dont understand why E values are used D:
Originally posted by theophilus:Several questions!
Inorganic Chem:
For transition metal complex right, how do you determine the coordination number. I understand that most of them are 6 but sometimes it can be 4 or 2, and i get stumped when i see the answer key. so how do i predict the coordination number?
Physical chem:
Do you mind explaining how do you predict solubility? isit as simple as polar solvents dissolve polar reagents and non polar dissolve non polar? refering to TYS 2009 P2 Q2(b) I dont understand why E values are used D:
For A level purposes, 3 simple concepts are relevant here : size of metal cation (if small, ie. period 2, only 4 ligands are possible, due to lack of vacant, energetically accessible d orbitals to accommodate an expanded octet), size of ligands (eg. water ligands small, so 6 are possible ; chloride ligands large, so only 4 are possible, to avoid excessive steric strain caused by van der Waals repulsions), charge on ligands (eg. water ligands neutral, so 6 are possible ; hydroxide ligands are negatively charged, so only 4 are possible, to avoid excessive steric strain caused by anionic repulsions between ligands).
Beyond these A level concepts, University level chemistry such as the Jahn-Teller effect, will be required to explain deeper questions on coordination complexes, eg. why [Cu(NH3)4]2+ has a square planar geometry instead of tetrahedral geometry.
Solubility is also a complex issue spread over several topics in the H2 syllabus, eg. chemical bonding, thermodynamics, solubility equilibria, Group 2, electrochemistry, organic chemistry, etc. The required answer at A levels depends on the context and H2 Chem syllabus topic that the question falls under. So there's no simple way to predict solubility (simple ways are for O levels, A levels are preparation for Uni level, in which everything becomes increasingly complex*). For the particular question you mentioned, falls under electrochem : only the oxidation potentials of Mg, Zn and Al, but not Cu, are sufficiently positive for their oxidation into aqueous and soluble metal cations when reacted with H+ from HCl (aq), to be thermodynamically feasible.
* In primary school, you thought you already knew everything in the Universe that could be known. In secondary school, you begin to realize you don't everything, but you still feel confident that you know almost everything. In JC and poly, you begin to understand that you don't really know all that much, and that the Universe is more complex than you thought. In University, you're humbled by the understanding that the Universe is so infinitely complex that you, and all sentient beings on Earth, actually know almost nothing relative to the infinitely vast Universe, but we know just enough to begin to appreciate and respect its beauty and complexity.
Great sir
Hi, is being able to solve A level questions sufficient? I am doing well on the TYS but prelim papers are ridiculously tough, isit unneccessarily tough?
Originally posted by theophilus:Hi, is being able to solve A level questions sufficient? I am doing well on the TYS but prelim papers are ridiculously tough, isit unneccessarily tough?
My advice would be to focus on the style of A level papers, but at the same time broaden your understanding by learning from the "ridiculously" difficult questions and mark schemes from the JCs. Unless of course, you already find A level papers difficult, in which case confusing yourself with the even tougher Prelim papers would be counter-productive.
Originally posted by UltimaOnline:
I guess you're right, I guess I've been pretty demoralised by prelim papers. But thanks so much for the advice, GOD BLESS
Why is 4-aminobenzenesulfonic acid a much weaker acid than benzenesulfonic acid?