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Originally posted by Flying grenade: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?
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.
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
Originally posted by Flying grenade: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
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?
Originally posted by supercat: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?
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.
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?
Originally posted by Flying grenade: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?
Originally posted by UltimaOnline:
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
Originally posted by Flying grenade: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
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.
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
Originally posted by Flying grenade: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
Originally posted by UltimaOnline:
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.
thanks for the 1st point. thanks for all the info
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?
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* !!!!!!!!!!!!!
Originally posted by Flying grenade: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?
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?
Originally posted by UltimaOnline:
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
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
Hi Ultima, hope u could examine this
qn : 2004 A level chemistry
https://www.dropbox.com/s/e5rkrmko3uhrac0/20160720_163024-1.jpg?dl=0 , part 2cii
my answer and teacher's answer
https://www.dropbox.com/s/0jqju117dpcdesm/20160720_163753-1.jpg?dl=0
my doubt : E°cell = 0.00V , can reaction still proceed/ thermodynamically favourable?
qn say 'two reagents mixed together'
can VO2+ form?
is it VO2+ can form because its aqueous medium, where H2O and H+ are present uh?
Originally posted by Flying grenade:Hi Ultima, hope u could examine this
qn : 2004 A level chemistry
https://www.dropbox.com/s/e5rkrmko3uhrac0/20160720_163024-1.jpg?dl=0 , part 2cii
my answer and teacher's answer
https://www.dropbox.com/s/0jqju117dpcdesm/20160720_163753-1.jpg?dl=0
my doubt : E°cell = 0.00V , can reaction still proceed/ thermodynamically favourable?
qn say 'two reagents mixed together'
can VO2+ form?
is it VO2+ can form because its aqueous medium, where H2O and H+ are present uh?
Vanadium's maximum OS is +5, not +3.
Based on standard oxidation potentials of V 3+, compared to the standard reduction potential of Cu+2 to Cu, you need only consider oxidation of V 3+ to VO 2+ (ie. OS of V = +4), and to nothing further (eg. to VO3 - or VO2 +) under standard conditions. But of course, the exam question can be more sadistic and replace V 3+ with V, and Cu2+ with a stronger oxidizing agent, then you need to consider each and of the possible oxidation products for vanadium all the way to +5, including memorizing (if asked by the question) all the color changes.
Minor point : Your teacher used the 'minus' version of the cell potential formula, but the 'plus' version is actually more meaningful, chemistry-wise (ie. for students & teachers who understand their chemistry more deeply).
Cell potential = Reduction potential @ Cathode + Oxidation potential @ Anode = (+0.34 V) + (-0.34V) = 0.00 V
If the calculated (standard or otherwise) cell potential is 0 V, it means the system with standard molarities on both sides of the equation would be at equilibrium (ie. Qc = Kc; it just so happens that in rare cases like this case, also that Kc = 1).
If the system is already at equilibrium, no net visible change occurs (since rate of forward reaction = rate of backward reaction, but be careful : k(forward) = k(backward) only if Kc = 1, a rare case). But note that at initial, you only mixed standard molarities (ie. 1M) of V 3+ and Cu 2+ together, which means Qc is not yet = Kc. Hence a net visible change will indeed occur, until Qc = Kc (which happens to be Kc = 1 in this reaction). But (your teacher didn't mention this) the reaction will be significantly slower (exactly how much slower, depends on kinetics and activation energy for the forward reaction), compared to if the calculated (standard or otherwise) cell potential was a lot more positive. This is because of the intimate relationship between electrochemistry and equilibria and kinetics.
(Flying Grenade, do you think your school JC students, or even your school JC teachers, already understand all the above?)
Yes Ultima, i always use ur edart terces version
the 'plus' version is actually more meaningful, chemistry-wise (ie. for students & teachers who understand their chemistry more deeply).
Cell potential = Reduction potential @ Cathode + Oxidation potential @ Anode
but cs toh advanced guide page 136 bottom of page qn 6 need use Cstoh's version, his version is E°cell = E°right - E°left
pls check this out https://www.dropbox.com/s/49a04pr1cwlsbg1/20160720_174449.jpg?dl=0
is it right to say that for any dynamic equilibrium, where the rate of forward reaction= equals rate of backward equation, and hence no net reaction in either direction, the kc=1 because k(forward) = k(backward) ?
oh , when Qc=Kc , and hence no net rxn, kc not necessarily always = 1? how abt a reversible rxn in dynamic eqm?