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Originally posted by Flying grenade:
for acid base reaction, not necessarily H2O is needed to be formed?
https://www.dropbox.com/s/end05thtc88s4jv/20160916_185541-1.jpg?dl=0
YJC 2016 prelim
-____-" Eh u O level or A level? Who says need water to be formed??? Only O levels then acid-base reactions need water to be formed. -_________-" -
ok,
so neutralisation is a subset of acid base reaction is it?
since standard enthalpy change of neutralisation is the energy released/evolved when one mol of H2O is formed from the rxn between an acid and an alkali under standard conditions of 298K , 1 atm
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am i correct to say that reaction is a lewis acid base reaction?
wait, the question clearly states that the oxide ion is acting as a bronsted lowry base.
am i right to say this, the reaction is a bronsted lowry acid base proton xfer rxn, oxide is the b.lowry base and NH3 is the b.lowry acid?
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Originally posted by Flying grenade:
ok,
so neutralisation is a subset of acid base reaction is it?
since standard enthalpy change of neutralisation is the energy released/evolved when one mol of H2O is formed from the rxn between an acid and an alkali under standard conditions of 298K , 1 atm
Neutralization is an O level term. Don't use it for A levels, other than "enthalpy of neutralization", which refers specifically to only those Bronsted-Lowry reactions that do generate H2O. -
Originally posted by Flying grenade:
am i correct to say that reaction is a lewis acid base reaction?
wait, the question clearly states that the oxide ion is acting as a bronsted lowry base.
am i right to say this, the reaction is a bronsted lowry acid base proton xfer rxn, oxide is the b.lowry base and NH3 is the b.lowry acid?
Yes. Bronsted-Lowry acid-base reactions are a subset of Lewis acid-base reactions. -
2008 p1/20
what is the product formed from the oxidation of alkene using Cold, Acidified, KMnO4?
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wow! also form diol(deduced as can form 1,2dibromocyclohexane)? same as cold alkaline kmno4
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for option A, we didnt learn that using HBr,heat , to a bromohydrin, can form bromo alkane. can we use this reaction ,write it in A levels?
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2008/p1/q26
cs toh writes NaCN is in the form of NaCN(aq)
so for the nu add of HCN to ketone to form cyanohydrin, reagents and conditons are HCN, trace KCN, 10-20°C
the NaCN is in (aq)form? not (s) form?
NaCN solid
https://en.m.wikipedia.org/wiki/Sodium_cyanide
or is it becos NaCN and KCN readily fumes in moist air(does it) ?
ok. Miss Angeline tan writes that the catalyst is CN-(aq)
in 10-20°C, HCN is in liquid state
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2008/p1/qn 40
i thought amino is used to refer to an amine group in an amino acid?
molecule in option 2 and 3 aren't amino acids right?
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The more u spam (ie. one shot post many qns), the less willing I am to look at ur qns, and thus the longer u'll have to wait.
As it is, I'll only look at ur qns and reply them only after midnight. If u spam some more qns in the meantime, maybe I'll reply u only 24 hrs later, 36 hrs, 48 hrs, etc.
Of course, if anyone else (in the hundreds of lurkers observing my Chem threads, and not all of you are JC students) volunteers to reply your questions in the meantime, pls go right ahead.
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Originally posted by Flying grenade:
wow! also form diol(deduced as can form 1,2dibromocyclohexane)? same as cold alkaline kmno4
Temperature factor outweighs pH factor for this reaction. Singapore JCs didn't teach u students that, huh. -
Originally posted by Flying grenade:
for option A, we didnt learn that using HBr,heat , to a bromohydrin, can form bromo alkane. can we use this reaction ,write it in A levels?
*facepalm* It's alkene, not halohydrin. And if u still say u didn't learn that, too bad for u, I'm pretty sure the rest of the Sg JC cohort did. -
Originally posted by Flying grenade:
2008/p1/q26
cs toh writes NaCN is in the form of NaCN(aq)
so for the nu add of HCN to ketone to form cyanohydrin, reagents and conditons are HCN, trace KCN, 10-20°C
the NaCN is in (aq)form? not (s) form?
NaCN solid
https://en.m.wikipedia.org/wiki/Sodium_cyanide
or is it becos NaCN and KCN readily fumes in moist air(does it) ?
ok. Miss Angeline tan writes that the catalyst is CN-(aq)
in 10-20°C, HCN is in liquid state
*facepalm*When u wanna add flavoring to ur food and u want the flavoring and food to mix well (for nice taste reaction to occur), would u just dump in a solid chunk of salt, or sprinkle soya sauce solution nicely spread out over the food?
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Originally posted by Flying grenade:
2008/p1/qn 40
i thought amino is used to refer to an amine group in an amino acid?
molecule in option 2 and 3 aren't amino acids right?
*faceplam's faceplam*U coconaden!!! Those are just the R group of amino acids lah!!!
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Originally posted by UltimaOnline:
*Those are just the R group of amino acids lahok yes i see now. so all the 3 options can form H-bonding between R groups. i understand liao. thanks ultima
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Originally posted by UltimaOnline:
*facepalm* It's alkene, not halohydrin. And if u still say u didn't learn that, too bad for u, I'm pretty sure the rest of the Sg JC cohort did.alkene + HBr(g) r.t. yields bromoalkane. i know this
see option A, 1st step cyclohexene + br2(aq) yields bromohydrin. thereafter 2nd step, HBr(g) + heat can yield 1,2dibromocyclohexane?
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Originally posted by UltimaOnline:
*facepalm*When u wanna add flavoring to ur food and u want the flavoring and food to mix well (for nice taste reaction to occur), would u just dump in a solid chunk of salt, or sprinkle soya sauce solution nicely spread out over the food?
thank you ! You are God !
i think there's a probablity that not many ppl know this unless they came across this qn.
no source(books or online) writes nacn(aq)
Unless it is implied? everyone is supposed to know nacn(aq) for the nu add?
haha, thank u ultima for all ur help !
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Originally posted by UltimaOnline:
Temperature factor outweighs pH factor for this reaction. Singapore JCs didn't teach u students that, huh.i see. then solvent not important mah. can just anyhow use a acidic, neutral, or alkaline medium. Cold will suffice, then why want teach us cold acidified or cold alkaline
oh is it because with cold alkaline, higher chance to get diol compared to acidic conditions? alkaline conditions provide larger chance for weaker oxidation , i.e. acidic conditions always more conducive for oxidation to happen compared to alkaline?
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Originally posted by Flying grenade:
alkene + HBr(g) r.t. yields bromoalkane. i know this
see option A, 1st step cyclohexane + br2(aq) yields bromohydrin. thereafter 2nd step, HBr(g) + heat can yield 1,2dibromocyclohexane?
Fair enuff, my bad, I misread.It's still in the H2 syllabus. Replacing OH with Br using HBr. Cambridge can ask u to draw the mechanism for this, but not many H2 students know how to draw it out. Do u ?
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Originally posted by Flying grenade:
i see. then solvent not important mah. can just anyhow use a acidic, neutral, or alkaline medium. Cold will suffice, then why want teach us cold acidified or cold alkaline
oh is it because with cold alkaline, higher chance to get diol compared to acidic conditions? alkaline conditions provide larger chance for weaker oxidation , i.e. acidic conditions always more conducive for oxidation to happen compared to alkaline?
No, it's not so simple. But A levels is simplified anyway (then what's O levels? let's not go there). So for A level purposes, if asked for reagents & conditions, go ahead and write "cold, alkaline, dilute KMnO4(aq)", but just be aware that the most important factor is temperature. Beyond this, is beyond A levels, don't confuse yourself by going there. -
Originally posted by Flying grenade:
thank you ! You are God !
i think there's a probablity that not many ppl know this unless they came across this qn.
no source(books or online) writes nacn(aq)
Unless it is implied? everyone is supposed to know nacn(aq) for the nu add?
haha, thank u ultima for all ur help !
As I said many times liao, don't OCD so much, don't worry so much, don't bother so much. Just write the reagents & conditions as given in trusted sources like CS Toh, Chan Kim Seng, or George Chong. And Cambridge isn't *that* anal, in this case they wouldn't even give a damn (ie. Cambridge will just ignore) whether u include the state symbol or not. -
Originally posted by UltimaOnline:
As I said many times liao, don't OCD so much, don't worry so much, don't bother so much. Just write the reagents & conditions as given in trusted sources like CS Toh, Chan Kim Seng, or George Chong. And Cambridge isn't *that* anal, in this case they wouldn't even give a damn (ie. Cambridge will just ignore) whether u include the state symbol or not.becos in this qn, need to deduce homogenous catalyst.
i was unsure nacn is s or aq state.
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oh ! question : in solid state , no nucleophilic reaction can happen? since cn- is locked?
(understand ur food analogy, reagents in aq state can be better spread out throughout the reactants compared to solid)
this applies for most reactions? no rxn between 2 molecules in their solid state
what about amine(gas) react with carboxylicacid(l) to form amide(s)
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Originally posted by Flying grenade:
oh ! question : in solid state , no nucleophilic reaction can happen? since cn- is locked?
(understand ur food analogy, reagents in aq state can be better spread out throughout the reactants compared to solid)
this applies for most reactions? no rxn between 2 molecules in their solid state
what about amine(gas) react with carboxylicacid(l) to form amide(s)
Obviously.Low yield, requires very high Ea, not an acceptable method for A level synthesis.