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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

UltimaOnline SG

Eh KNN lah Flying Grenade, I see so many qns already super turned off, sibei sian. I told u, ask 1 qn at a time! I won’t reply any of ur qns, until u delete (save it on ur own phone as txt document) ur qns, and leave only 1 qn on the forum at a time.

UltimaOnline SG

can individual amino acids (residues ) lys and ser undergo neutralisation?

what is the R group interaction between lys and ser in a protein? is it ionic interaction as a result of neutralisation between the R groups? or is it H bonding? or is it indeed ionic interactions, but for reason idk

can neutralisation between R groups occur within the protein?

First of all, "neutralization" is an O level term. At A levels, the only time you're allowed to use this term is "enthalpy of neutralization". For physical chemistry, you must state "Bronsted-Lowry acid-base reaction". For organic chemistry, you must state "proton transfer reaction". Using "neutralization" will get you penalized at A levels.

Ser's R group is an aliphatic alcohol, non-acidic OH group. Lys' R group is amine/ammonium. Hence R group interactions between Lys and Ser is hydrogen bonding.

To your next question, the answer is "obviously", but also "you're thinking it wrongly". If you have a deeper understanding of Chemistry, you'll realize that the protonation or deprotonation is not actually between particular R groups and other particular R groups (eg. "Asp transfers proton to Lys", etc), but each R group protonation/deprotonation actually occurs with the aqueous solvent environment in the biological organism (eg. human body tissue fluids). In other words, solvent catalysed Bronsted-Lowry acid-base proton transfer reactions.

Flying grenade SG

Thanks, Ultima !!!

omg , difficult qn

online no S2- and S22- structure

Alevel 2014/p2/qn2dii

ultima can help check my drawing of disulfide ion, S22- , if it is correct

https://www.dropbox.com/s/5e2za7uiwdmge1x/20160719_135608.jpg?dl=0

S can expand octet

the answer provided by publisher no additional 2 electrons

UltimaOnline SG

Thanks, Ultima !!!

omg , difficult qn

online no S2- and S22- structure

Alevel 2014/p2/qn2dii

ultima can help check my drawing of disulfide ion, S22- , if it is correct

https://www.dropbox.com/s/5e2za7uiwdmge1x/20160719_135608.jpg?dl=0

S can expand octet

the answer provided by publisher no additional 2 electrons

Wrong lah. S2- is 4 lone pairs, 0 bond pair for that 1 S atom. S2 2- is 3 lone pairs, 1 bond pair, for each S atom with a uninegative formal charge, hence dinegative ionic charge.

supercat SG

http://imgur.com/oMkVJ6s

Is this the correct mechanism for E1 & E2?

Can see that this reaction needs alkaline medium. So that there would be alkoxide formation which can attack the molecule. Correct??

For LiAlH4, why does it only reduce ketones/aldehydes, but for H2 & Nickel catalyst, it reduces all alkenes, ketones, aldehydes?

UltimaOnline SG

http://imgur.com/oMkVJ6s

Is this the correct mechanism for E1 & E2?

Can see that this reaction needs alkaline medium. So that there would be alkoxide formation which can attack the molecule. Correct??

For LiAlH4, why does it only reduce ketones/aldehydes, but for H2 & Nickel catalyst, it reduces all alkenes, ketones, aldehydes?

Yes, your E1 and E2 mechanisms are correct. But if you're using alkoxide ion as the base, then the correct reason why you need alkaline pH is to prevent protonation of your alkoxide base, so it can carry out the elimination.

Alkene is a nucleophile, as is also the H- ion from LiAlH4 and NaBH4, hence no reaction occurs (they're not gay). In contrast, H2(g) with nickel catalyst is able to provide both H+ and H- (as consequence of H2 adsorption-reaction-desorption with the transition metal catalyst with partially filled d orbitals), and hence can hydrogenate the alkene nucleophile / base.

Flying grenade SG

pg 253 cs toh advanced guide, the other examples with [CuCl4]2- , for Co-ordination number 4, sq planar, are all affected by Jahn-Teller effect right?

UltimaOnline SG

pg 253 cs toh advanced guide, the other examples with [CuCl4]2- , for Co-ordination number 4, sq planar, are all affected by Jahn-Teller effect right?

The Jahn-Teller distortion is particularly notorious (and you're required by the A level syllabus to memorize this example) for the deep blue tetraamminecopper(II) coordination complex ion. All other 4 ligand coordination complexes, eg. tetrachlorocuprate(II), must be assumed to be tetrahedral, unless hints (eg. cis and trans isomers exist for a 4 ligand coordination complex) are given by the question that it's square planar.

Flying grenade SG

Wrong lah. S2- is 4 lone pairs, 0 bond pair for that 1 S atom. S2 2- is 3 lone pairs, 1 bond pair, for each S atom with a uninegative formal charge, hence dinegative ionic charge.

Thanks Ultima savior, got it

i was careless, publisher's answer is indeed correct

why my drawing wrong? its plausible since S can expand octet, and its more thermodynamically favourable to form double bond

UltimaOnline SG

Thanks Ultima savior, got it

i was careless, publisher's answer is indeed correct

why my drawing wrong? its plausible since S can expand octet, and its more thermodynamically favourable to form double bond

1stly, how are you going to achieve a dinegative ionic charge without 2 uninegative formal charges? And how are you going to achieve 2 uninegative formal charges for the 2 S atoms, unless each S atom has 3 lone pairs and 1 bond pair?

2ndly, you're wrong, it's actually more thermodynamically favorable for period 3 elements to form more single bonds instead of double bonds, which is why CO2 has double bonds while SiO2 has single bonds, another classic example being nitrogen versus phosphorus molecules, etc. And do you know the correct explanation for this? Go ask your school teacher or private tutor, don't ruin the fun for others on the forum by posting the answer here.

Flying grenade SG

is it becos sio2 is a giant covalent molecule with giant covalent structure, in order to have this structure lattice of atoms bonded tetrahedrally, and therefore need single bond?

is it e.g. if P form 5 single bonds as in PCl5, more energy released as compared if it would form double bond? woah, tried googling for this, cant find the answers

UltimaOnline SG

is it becos sio2 is a giant covalent molecule with giant covalent structure, in order to have this structure lattice of atoms bonded tetrahedrally, and therefore need single bond?

is it e.g. if P form 5 single bonds as in PCl5, more energy released as compared if it would form double bond? woah, tried googling for this, cant find the answers

Eh follow simple instructions can or not? I said, DON'T POST THE ANSWERS HERE ON THE FORUM. Go check with your school teacher or private tutor for the answers.

Flying grenade SG

thanks for the 1st point. thanks for all the info

Flying grenade SG

for A levels, is it redundant, or Wrong, to draw the circle valence shell for drawing of dot and cross structures?

no need draw the circle representing the valence shell, just draw valence electrons will do right?

Flying grenade SG

for Chemistry Students

the bs statement : at low pressures, "Volume of an ideal gas occupies is negligible compared to the volume of container" is , *angrily* WRONG.

if u want, it shld be vol of ideal gas *Molecules* being negligible compared to vol of container

from cs toh chemistry books :

at low pressures, *Gas molecules are widely spaced and so, have negligible size, Since volume occupied by gas is very large compared to the gas molecule itself* !!!!!!!!!!!!!

UltimaOnline SG

for A levels, is it redundant, or Wrong, to draw the circle valence shell for drawing of dot and cross structures?

no need draw the circle representing the valence shell, just draw valence electrons will do right?

1stly, my typo error in a previous post. Statement should be, "How are you going to achieve a dinegative ionic charge without 2 uninegative formal charges?"

2ndly, the circle representing the valence shell is not required for A levels, but it's not wrong to draw it either, just not compulsory.

3rdly, you mean your school (Singapore JC) teacher and lecture notes taught the entire school (ie. hundreds of JC students) this wrong ideal gas statement?

Flying grenade SG

1stly, my typo error in a previous post. Statement should be, "How are you going to achieve a dinegative ionic charge without 2 uninegative formal charges?"

2ndly, the circle representing the valence shell is not required for A levels, but it's not wrong to draw it either, just not compulsory.

3rdly, you mean your school (Singapore JC) teacher and lecture notes taught the entire school (ie. hundreds of JC students) this wrong ideal gas statement?

*angrily* YES, yessss , year after year, batches after batches, hundredssss of undiscerning jc students (the discerning and critical thinking ones would be unaffected )

i only discovered and rectified this mistake by myself after 2 years !!!!!

for my school, im nt sure abt the lecture notes, troublesome, segregated, unclear, may be good or not I'm not sure since I don't use them. and have already thrown it away

it's several teachers in my sch in person verbalise it wrongly

Flying grenade SG

god bless education in the whole wide worldwide to learn and teach the correct stuffs please

god's plan/ destined/predestined that i wasnt discerning, mature, critical, curious, enthusiastic, earnest in the study and the critical thinking of science and learning and studying, i started and discovered late, to my own detriment

just do my best in life from now onwards

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