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last SG · 2015-08-19T22:54:00+00:00

Topic : atomic radius Hi! This is from singapore cambridge nov a level exam year 2010,Paper 1 qn 1Qn: which element has the largest atomic radius?BrKKrScSo...

Flying grenade SG

恩 .

Flying grenade SG

2012/p2/qn 3a

what would be seen in the container after agcl is left 1 hr in daylight?

why ag+ will be reduced to ag(s) ? is it becos sunlight and oxygen oxidise cl- into cl2(g) , then ag+ become ag(s) ah??

shinglee's 2016 soln by mark ong state that "white ppt turned dark grey/black due to reduction of ag+ to ag "

from wiki, ag(s) is a "lustrous white metal"

from jc book and notes, i thought ag is silver(mirror) appearance? why would it be dark grey or black?

Flying grenade SG

page 292 cs toh advanced guide

would my translation be appropriate : "some strain in the ring" instead of "some puckering of the ring" by cs toh?

Flying grenade SG

page 292 cs toh.

eh actually, how would one determine if a molecule is planar or not?

in cyclobutane, all the C atoms are connected to 4 groups, electronic geometry is tetrahedral in the 1st place, how can it be (trigonal or square) planar?

is it to determine if a molecule is planar or not, all the atoms in the main chain in the molecule(example C, N, O) ,must all have same bond angles ah?

UltimaOnline SG

2012/p2/qn 3a

what would be seen in the container after agcl is left 1 hr in daylight?

why ag+ will be reduced to ag(s) ? is it becos sunlight and oxygen oxidise cl- into cl2(g) , then ag+ become ag(s) ah??

shinglee's 2016 soln by mark ong state that "white ppt turned dark grey/black due to reduction of ag+ to ag "

from wiki, ag(s) is a "lustrous white metal"

from jc book and notes, i thought ag is silver(mirror) appearance? why would it be dark grey or black?

Warning for FlyingGrenade : do not spam too many qns at one shot, or I'll ignore all ur qns. Just post 1 at a time, wait patiently for up to 24 hours for me to reply ur 1st qn, then post ur next qn.

Yes, UV light in sunlight provides the Ea for the redox reaction. When silver is exposed to air, it oxidizes into black silver(I) oxide.

UltimaOnline SG

page 292 cs toh advanced guide

would my translation be appropriate : "some strain in the ring" instead of "some puckering of the ring" by cs toh?

No. Puckering (ie. 3 dimensional conformation) is a means by which the ring seeks to minimize ring strain due to angle strain.

UltimaOnline SG

page 292 cs toh.

eh actually, how would one determine if a molecule is planar or not?

in cyclobutane, all the C atoms are connected to 4 groups, electronic geometry is tetrahedral in the 1st place, how can it be (trigonal or square) planar?

is it to determine if a molecule is planar or not, all the atoms in the main chain in the molecule(example C, N, O) ,must all have same bond angles ah?

CS Toh is referring to planarity (ie. whether or not the molecule is planar, but it isn't! even when) in regard to C atoms only. Cambridge will specify in regard to which atoms.

Not necessarily all the same bond angles, but rather that each atom's molecular geometry must be planar (ie. linear or trigonal planar).

Flying grenade SG

https://www.dropbox.com/s/l9ndyy09c4e1qfj/Screenshot_2016-06-22-20-42-44-1.png?dl=0

so cyclobutane exists as conformers is it?

from the pic above by cyclo butane wiki page, how does the molecule looks like it's planar?

for both conformers, there seems to be a total of 4 planes that the molecule is oriented at

so the C atoms in cyclobutane force its own molecular geometry to be trigonal planar when its electronic geometry is tetrahedral?

UltimaOnline SG

https://www.dropbox.com/s/l9ndyy09c4e1qfj/Screenshot_2016-06-22-20-42-44-1.png?dl=0

so cyclobutane exists as conformers is it?

from the pic above by cyclo butane wiki page, how does the molecule looks like it's planar?

for both conformers, there seems to be a total of 4 planes that the molecule is oriented at

so the C atoms in cyclobutane force its own molecular geometry to be trigonal planar when its electronic geometry is tetrahedral?

It's not planar. Wiki says it's not planar. CS Toh says it's not planar. Why do u keep obsessing about it being planar? No, the C atoms do NOT "force its own molecular geometry to be trigonal planar", because cyclobutane isn't planar. Enuff nonsense. Anything further on this, ask ur school teacher or private tutor.

Flying grenade SG

ooh sorry haha i read the sentence wrongly in cstoh's page

Flying grenade SG

" ion - permanent dipole interactions are stronger than hydrogen bonding, as long as the formal charge is on a small period 2 atom. "

hi ultima, may i ask, what is the comparison?

ion permanent dipole interactions between nh4+ and h2o molecules, and H bond between nh3 and h2o ah?

Flying grenade SG

when do we use miscible and soluble?

is NH3 miscible and/or soluble with/in water?

UltimaOnline SG

" ion - permanent dipole interactions are stronger than hydrogen bonding, as long as the formal charge is on a small period 2 atom. "

hi ultima, may i ask, what is the comparison?

ion permanent dipole interactions between nh4+ and h2o molecules, and H bond between nh3 and h2o ah?

Best to compare phenoxide vs phenol (ie. addition of OH-), phenylammonium vs phenylamine (ie. addition of HCl), in terms of increased solubilities (as a consequence of ion - permanent dipole being stronger than H bonds, or alternatively, H bonds strengthened by formal charges).

U prolly won't understand this fully, go ask ur school teacher or private tutor, instead of annoying me by flogging the dead horse as u are wont to do (ie. keep asking qns subsequently & repeatedly on the same topic, coz u dun understand my replies, that's damn annoying).

UltimaOnline SG

when do we use miscible and soluble?

is NH3 miscible and/or soluble with/in water?

If a solute is miscible with a solvent, then the solute is considered to be soluble in that solvent.

Flying grenade SG

If a solute is miscible with a solvent, then the solute is considered to be soluble in that solvent.

swee, thx thx

miscible for liquids, soluble for solids

Flying grenade SG

OOOOHH THANKS ULTIMA !!!!!

i understand this reply haha thanks

ArJoe SG

Hi, for a level 2015 paper 2 question 3bi, i said to provide energy to overcome the actication energy of the reaction. Or should i say to provide the energy to for cl2 to homolytic fission?
for 3biii, i said the homolytic fission of cl2 release free chlorine radicals which are very reactive, and they initiate a chain reaction with h2 gas.hence reaction becomes increasingly faster.
for 4bii, cause ch3i is a primary iodoalkane, resulting in less steric hindrance around the c atom. It cannot undergo sn1 because of the because the carbocation intermediate produced is very unstable.
are my answers acceptable?

UltimaOnline SG

You should say both "activation energy" and "to homolytically cleave the Cl-Cl bond".

Insufficient : you must specify that the propagation steps increase the molarity of the reactant free radicals, hence increasing the rate of reaction as predicted by the rate equation.

Yes, your answer is ok.

Flying grenade SG

"A chemical reaction is spontaneous if it is thermodynamically feasible, ie. Gibbs free energy change is negative."

from : http://sgforums.com/forums/2297/topics/488922

i thought that for a reaction to be spontaneous, must be both thermodynamic feasible and kinetically feasible?

backed up by this " Spontaneity implies both kinetic feasibility as well as thermodynamic feasibility. "

from : http://sgforums.com/forums/2297/topics/489346

e.g. diamond to graphite thermodynamically favourable/feasible, but kinetically not favourable/feasible

can't think of an example where a reaction is kinetically favourable, but not thermodynamically feasible

Flying grenade SG

wow, that thread regarding the discussion of energetics is awesome

another good learning point :important point that systems can be viewed in either isolation or coupled.

Examples of thermodynamically non-feasible or non-spontaneous reactions from H2 Biology that certainly continue to occur (otherwise you wouldn't be alive to read this), would be photosynthesis and protein synthesis.

woah yes, just recalled ,that a reaction with Positive change in gibbs free energy can still occur ! e.g. photosynthesis, which requires a continuous supply of energy from sunlight

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