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Ester(l) + amine(g) -> amide(s) . this is in ks chan book too, not only in M.S. notes
acylhalide(l) + amine(g) -> amide(s)
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why high ea for carboxylic acid and amine
magnitude of delta +ve on C atom of carboxyl group not large enough?
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Originally posted by Flying grenade:
Ester(l) + amine(g) -> amide(s) . this is in ks chan book too, not only in M.S. notes
acylhalide(l) + amine(g) -> amide(s)
Duh. Notice the reactants are not (s). So why does it surprise u these reactions would work? -
Originally posted by Flying grenade:
why high ea for carboxylic acid and amine
magnitude of delta +ve on C atom of carboxyl group not large enough?
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formation of amide from carboxylic acid and amine is a reversible reaction
http://www.chemguide.co.uk/organicprops/amides/preparation.html
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Originally posted by Flying grenade:
formation of amide from carboxylic acid and amine is a reversible reaction
http://www.chemguide.co.uk/organicprops/amides/preparation.html
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Originally posted by UltimaOnline:
Step 1 : Cl2 in CCl4, in the dark at rtp, halogenation via electrophilic additionStep 2 : NaOH in ethanol, heat under reflux, dehydrohalogenation elimination via E2 mechanism
this is at pg 62 of this thread
for step 2, isn't it elimination/dehalogenation of haloalkane to alkene? the molecule is 1,2-dichloroethane. why is it dehydrohalogenation?
do we need to know the reagents and conditions and mechanism for dehydrohalogenation of halohydrin to alkene? we didnt learn it
what are the R&C for dehydrohalogenation of halohydrin to alkene?
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2010/p1/26
i see, NaBH4 is in dry ether right? as in not solid nor aqueous
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2010 p3 qn 1
oh yes, Cl2(g) can react with 1/3I2(s) to form 2/3ICl3(l)
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2010 p3 qn 1b
Miss Angeline Tan writes question require us to compare in terms of rates of rxn and not extent of rxn
I understand the qn and solution, dont need address this qn
i just thought of this
most of the time, rates of rxn and extent of reaction are corresponding/correlated/proportional, e.g. rate of rxn increase, so does extent of reaction
But are they related(as in stems from the same reason/cause, or are linked to each other)?
are all, or most, rates of rxn increase, extent of reaction also increase, vice versa?
in this case of reactivity of Halogens with Hydrogen, i think , reactivity decreases down group 17, as the H-X bond becomes longer and weaker, hence both rate and extent of reaction decreases.
i think its ok to discuss abt rate and extent of rxn, for this qn
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interestingly, Cambridge asked 'explain what is meant by the term pka as applied to weak acid HA' , N2010/p3/2ai
do i write cs toh version :
https://www.dropbox.com/s/tjo3mm26b78505c/20160918_161815-1.jpg?dl=0
or
the pKa value of a weak acid is the pH whereby there is equal molarities of cj acid and cj base ([HA] and [A-]) , this pKa value also corresponds to the pH at max buffering capacity of a buffer ,and occurs at half neutralisation point
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Originally posted by Flying grenade:
this is at pg 62 of this thread
for step 2, isn't it elimination/dehalogenation of haloalkane to alkene? the molecule is 1,2-dichloroethane. why is it dehydrohalogenation?
do we need to know the reagents and conditions and mechanism for dehydrohalogenation of halohydrin to alkene? we didnt learn it
what are the R&C for dehydrohalogenation of halohydrin to alkene?
U confuse "hydro" with "hydroxyl". Not in syllabus. -
Originally posted by Flying grenade:
2010/p1/26
i see, NaBH4 is in dry ether right? as in not solid nor aqueous
NaBH4 (ethanol). -
Originally posted by Flying grenade:
2010 p3 qn 1b
Miss Angeline Tan writes question require us to compare in terms of rates of rxn and not extent of rxn
I understand the qn and solution, dont need address this qn
i just thought of this
most of the time, rates of rxn and extent of reaction are corresponding/correlated/proportional, e.g. rate of rxn increase, so does extent of reaction
But are they related(as in stems from the same reason/cause, or are linked to each other)?
are all, or most, rates of rxn increase, extent of reaction also increase, vice versa?
in this case of reactivity of Halogens with Hydrogen, i think , reactivity decreases down group 17, as the H-X bond becomes longer and weaker, hence both rate and extent of reaction decreases.
i think its ok to discuss abt rate and extent of rxn, for this qn
Kc = kf / kb -
Originally posted by Flying grenade:
interestingly, Cambridge asked 'explain what is meant by the term pka as applied to weak acid HA' , N2010/p3/2ai
do i write cs toh version :
https://www.dropbox.com/s/tjo3mm26b78505c/20160918_161815-1.jpg?dl=0
or
the pKa value of a weak acid is the pH whereby there is equal molarities of cj acid and cj base ([HA] and [A-]) , this pKa value also corresponds to the pH at max buffering capacity of a buffer ,and occurs at half neutralisation point
Use CS Toh's answer. -
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2014 IJC prelim p1 q16, how come answer is D?i thought electrical conductivity increases from na to al?
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Originally posted by ArJoe:
2014 IJC prelim p1 q16,
how come answer is D?i thought electrical conductivity increases from na to al?
Yes, but the question states *general* decrease, so even though it increases slightly from Na to Al, but in *general*, electrical conductivity decreases from metals (LHS of periodic table) to non-metals (RHS of periodic table).For MCQs, choose the *best* option available, even if it's not totally correct. For this particular MCQ, the other 3 options are even more obviously wrong.
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Arhhhhh so misleading!! I hope a level dosent come out such questions.. Thanks for your prompt reply!
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Originally posted by ArJoe:
Arhhhhh so misleading!! I hope a level dosent come out such questions.. Thanks for your prompt reply!
No prob. And every year Sg A levels will have 2 or 3 MCQs which are ambiguous and problematic, for which even JC teachers disagree on what's the best answer.But it's a bell-curve afterall, so if it's not fair for everyone, it's still fair. Woot! - BedokFunland JC
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So what do you think about the a level practical paper 5 for private candidates? Do you even prepare for it? Cus I rmb u were crushing H2 Chem without planning and practical? wuttt ?
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Originally posted by theophilus:
So what do you think about the a level practical paper 5 for private candidates? Do you even prepare for it? Cus I rmb u were crushing H2 Chem without planning and practical? wuttt ?
Yeah, *I* can skip my Planning and my Pract Paper, and I always get my A grade. But dude, *you're* not me. Go buy and study Chan Kim Seng's H2 Chem Planning Book. That's also the only way you can prepare for your Pract Paper. -
hahaha yeap, i am definately not at that level LOL. But are there like a fixed set of chemical experiments?
Also is it true that JC students generally ace their SPA?
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Originally posted by theophilus:
hahaha yeap, i am definately not at that level LOL. But are there like a fixed set of chemical experiments?
Also is it true that JC students generally ace their SPA?
No, nothing fixed. But *usually* (not always) involves titration and QA, plus one additional question which does not need (ie. don't!) to be carried out. Just interpret the data to answer the questions.Not true. Don't worry about comparing with JC students.
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Oh no as in not fixed chem questions, but like they have only fixed library of experiments for the a level syllabus? I actually have the planning book and there are only 10 experiment types. Generally these 10 will do?
haha how not to! bell curve man, but yeah la I guess will have to theoretically study practical