THANKSSSS ULTIMAAAAAA !!!
for electrochemical cell, does Pt/Carbon electrode have to be partially submerged? or doesn't matter if it's fully submerged
for both S.H.E half cells and not S.H.E half cells, the half cell on the right using Pt as electrode
I think can be safe to just draw half submerged Pt(s) for both S.H.E and non-S.H.E half cells that uses Pt(s)
can employ seperation techniques to obtain pure ethanol etc
can use seperation techniques to obtain pure HCl, H2SO4? if not, why not? if yes, why? is it in practice, we need and utilise dilute acids and conc acids, but not pure acids?
is it acids means in the presence of H2O, so H+ will be dissociated? so all acids must have H2O present, and so, not pure? ok there's such thing as pure HCl(g). but for H2SO4 is made from SO3(g) , so there's pure SO3(g)
then why there can be pure ethanol, but no such thing as pure HCl acid (i know make from hcl gas) ? or pure (strong) acids?
Originally posted by Flying grenade:can employ seperation techniques to obtain pure ethanol etc
can use seperation techniques to obtain pure HCl, H2SO4? if not, why not? if yes, why? is it in practice, we need and utilise dilute acids and conc acids, but not pure acids?
is it acids means in the presence of H2O, so H+ will be dissociated? so all acids must have H2O present, and so, not pure? ok there's such thing as pure HCl(g). but for H2SO4 is made from SO3(g) , so there's pure SO3(g)
then why there can be pure ethanol, but no such thing as pure HCl acid (i know make from hcl gas) ? or pure (strong) acids?
2014 pre u paper 3 , qn 3ciii
i know kc only changes with temperature.
but as eqm shifts right, molarity of pdt increases whereas molarity of rxt decreases, why value of kc doesn't change?
Reason why Kc does not change with changes in Concentration and pressure can be found here
best link : http://www.chemguide.co.uk/physical/equilibria/change.html
understood alr. Thank you Jim Clark.
additional links :
http://chemistry.stackexchange.com/questions/4977/le-chateliers-principle-how-can-the-equilibrium-shift-while-kc-remains-consta
http://chemistry.stackexchange.com/questions/49225/why-is-kc-not-affected-by-change-in-pressure
when asked to 'give equation for the reaction'
e.g. pre u paper 2014 p3 qn 5b ii
can we draw the molecules, instead of giving
C6H5OH + 3Br2 → C6H2Br3OH + 3HBr? will it be marked correct?
Originally posted by Flying grenade:when asked to 'give equation for the reaction'
e.g. pre u paper 2014 p3 qn 5b ii
can we draw the molecules, instead of giving
C6H5OH + 3Br2 → C6H2Br3OH + 3HBr? will it be marked correct?
In the context of your particular question, if all you mean is drawing out the benzene ring, yes it's acceptable to do so (instead of just writing the formula), particularly since in this case phenol is tribrominated (on all 3 of the ortho and para positions) and hence in this case there are no positional isomer ambiguity problems (eg. if it was only monobrominated or dibrominated, then you would have a mixture of different positional isomers, in which case it would be more correct to write the condensed structural formula C6H4BrOH instead of drawing it out).
Originally posted by UltimaOnline:
Depends on context. Even in contexts where drawing out the structures and/or mechanisms is acceptable by Cambridge as an alternative to the written equation, you'll need to be careful in the stoichiometry and balancing the reaction correctly. If unsure of acceptability of context, always play safe and give both (ie. draw out structures and/or mechanism if it helps you, *and* write out the balanced equation), as long as you know your chemistry well and have good time management.In the context of your particular question, if all you mean is drawing out the benzene ring, yes it's acceptable to do so (instead of just writing the formula), particularly since it's tribrominated on the ortho and para positions and there are no position isomer ambiguity problems.
ah yes ok. sometimes it's better to draw out(instead of writing molecular formula), leaving no ambiguity for position isomers problems
Originally posted by Flying grenade:ah yes ok. sometimes it's better to draw out(instead of writing molecular formula), leaving no ambiguity for position isomers problems
Originally posted by UltimaOnline:
I've edited my post with further elaboration.
OH wow i see hahaa. okay thanks Ultima ! i've understood
2015 TPJC p1 qn 19. dont understand the soln and dk how get the answer.
a thought of mine is this , why can't [Pt(NH3)6]4+.4Cl- then?
just realised cstoh book dont have zaitsev's rule
does zaitsev's rule apply for E1 and E2 ?
Originally posted by Flying grenade:2015 TPJC p1 qn 19. dont understand the soln and dk how get the answer.
a thought of mine is this , why can't [Pt(NH3)6]4+.4Cl- then?
Zaitsev stated, "The alkene formed in greatest amount is the one that corresponds to removal of the hydrogen from the β-carbon having the fewest hydrogen substituents.
Originally posted by Flying grenade:just realised cstoh book dont have zaitsev's rule
does zaitsev's rule apply for E1 and E2 ?
Originally posted by UltimaOnline:
Your formula has 4 Cl- counter ions, while the question specified 2 Cl- counter ions (you gotta know how to interpret the question correctly, even if they don't phrase it as well as I would if I were to set the question).
ahhh.. okay ! i got it alr. thanksss ultima !!!
iodoform reactions
cs toh book
for alcohol : https://www.dropbox.com/s/0h96ncqt79kcc41/20160808_111502.jpg?dl=0
for ketone : https://www.dropbox.com/s/501tqbgeyehnjhc/20160808_111733-1.jpg?dl=0
K.S.Chan organic book
for alcohol : https://www.dropbox.com/s/62wvumam9p7g396/20160808_112030.jpg?dl=0 and https://www.dropbox.com/s/ohzulxry4jccn2v/20160808_112058-1.jpg?dl=0
for ketone :
https://www.dropbox.com/s/r5yu6ek7drqvafa/20160808_112221-1.jpg?dl=0
https://www.dropbox.com/s/t2ujguhavojz274/20160808_112306-1.jpg?dl=0
https://www.dropbox.com/s/f8ic72njovjpd3e/20160808_112351-1.jpg?dl=0
why cs toh reactions no H2O, but have HI ? whereas KSChan's reactions have H2O, and I-
and the stoichiometric ratio all different
iodoform reactions need memorise? which one to memorise?all?
Originally posted by Flying grenade:iodoform reactions
cs toh book
for alcohol : https://www.dropbox.com/s/0h96ncqt79kcc41/20160808_111502.jpg?dl=0
for ketone : https://www.dropbox.com/s/501tqbgeyehnjhc/20160808_111733-1.jpg?dl=0
K.S.Chan organic book
for alcohol : https://www.dropbox.com/s/62wvumam9p7g396/20160808_112030.jpg?dl=0 and https://www.dropbox.com/s/ohzulxry4jccn2v/20160808_112058-1.jpg?dl=0
for ketone :
https://www.dropbox.com/s/r5yu6ek7drqvafa/20160808_112221-1.jpg?dl=0
https://www.dropbox.com/s/t2ujguhavojz274/20160808_112306-1.jpg?dl=0
https://www.dropbox.com/s/f8ic72njovjpd3e/20160808_112351-1.jpg?dl=0
why cs toh reactions no H2O, but have HI ? whereas KSChan's reactions have H2O, and I-
and the stoichiometric ratio all different
iodoform reactions need memorise? which one to memorise?all?
CS Toh's equation occurs first to generate HI, then since OH- is in excess, all the HI will undergo Bronsted-Lowry acid-base proton transfer reaction to generate Chan Kim Seng's equation. Better to write Chan Kim Seng's equation in the A levels.
Originally posted by UltimaOnline:
Only if you can't intelligently balance it out yourself (it's a redox reaction after all, so you should be able to work out the coefficients yourself using half-equations), then memorize the coefficients. Yes, all.CS Toh's equation occurs first to generate HI, then since OH- is in excess, all the HI will undergo Bronsted-Lowry acid-base proton transfer reaction to generate Chan Kim Seng's equation. Better to write Chan Kim Seng's equation in the A levels.
Ahh !! okay, i see !!!
thanks ultima for your reply help clear my doubts !!
my cher say if qn nvr ask u to use P4 or S8, always just use P or S.
cambridge papers not epic fail as jc prelim papers, and the qn they set will always specify to use P , P4, S, or S8 right?
for oxidation of alcohol to carbonyl compounds
cs toh writes
acidified kmno4, heat
k.s.chan writes Kmno4(aq), H2SO4(aq), heat
elimination of alkyl halides to alkene
cs toh writes ethanolic KOH
k.s.chan writes KOH, ethanol
i think I'll follow k.s.chan
Originally posted by Flying grenade:my cher say if qn nvr ask u to use P4 or S8, always just use P or S.
cambridge papers not epic fail as jc prelim papers, and the qn they set will always specify to use P , P4, S, or S8 right?
cis-trans geometric isomerism cannot exist for double bonds in ring?
trans isomer cannot exist , only cis exists?
only for ring sizes with more than 20C atoms, then have cis trans isomers?