Chemistry: Post your doubts here!

[Roe Mir]

Guys does anyone have the marking scheme for October-November 2002 paper 1?

 

[student2]

is an acid or salt produced whn aldehyde reacts with tollens/fehlings?

 

[fahadhameedahmad]

For this question at anode, won't it be OH- that gets oxidized? Why H2O?

concentration of OH- and H+ ions is too low in aqueous solutions, so this is different from O'levels
never use or show H+ or OH- ions

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[fahadhameedahmad]

acid

is an acid or salt produced whn aldehyde reacts with tollens/fehlings?

acid produced

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[student2]

acid

acid produced

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thnxx. cud u also tell y gly-ala is nt the same as ala-gly? (peptides)

 

[darks]

is there any rule for this kind of cis trans isomerism?? how to deduce the isomer structures?

 

[fahadhameedahmad]

thnxx. cud u also tell y gly-ala is nt the same as ala-gly? (peptides)

On left side is ammine and on right side is carboxylic in amino acid

Now ala-gla means ala's amine bonds with gla's acid group forming peptide

Gla-ala would be oppositte

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[fahadhameedahmad]

View attachment 62133
is there any rule for this kind of cis trans isomerism?? how to deduce the isomer structures? View attachment 62134

Mostly guessing by changing orientation

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[AnonymousX9]

Oct/Nov 2016 p42 question 8(d) pls help... how do I determine the number of protons in the table from the graph?

 

[fahadhameedahmad]

can some plzz explain?
9701_w16_qp_41

 

[AnonymousX9]

Feb/March 2016 p42 question 9 (c) part ii, how do we figure out the number of different dipeptides that can be formed in the reaction between 2 amino acids (T and U)?? Is there a generalized easier way rather than to have to draw all of them out one by one?? Pls help.

 

[AnonymousX9]

View attachment 62133
is there any rule for this kind of cis trans isomerism?? how to deduce the isomer structures? View attachment 62134

I have the same query. Been trying since days but I can't figure out how do we determine which is the cis and which is the trans isomer in 6 coordinate complexes and how to draw the structures??

 

[student2]

View attachment 62133
is there any rule for this kind of cis trans isomerism?? how to deduce the isomer structures? View attachment 62134

HELLNO

 

[darks]

Mostly guessing by changing orientation

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It can't be that... i mean by guessing, people would get it wrong 90% of the times... or are we allowed more structures than the ms? I don't think so though as ER for these questions most of the times states that a lot of people found it difficult.

 

[techgeek]

View attachment 62133
is there any rule for this kind of cis trans isomerism?? how to deduce the isomer structures? View attachment 62134

I have the same query. Been trying since days but I can't figure out how do we determine which is the cis and which is the trans isomer in 6 coordinate complexes and how to draw the structures??

It's called 'fac' 'mer' isomerism. Because around the metal, the 6 ligands form an octahedron which can go in 3 different different directions so form 2 different isomers.
First you need to understand that there are 3 directions and really imagine them in your head this way, when you look at the complex.
Simple line --- plane of the paper
wedges --------bonds towards the viewer
dashed --------bonds away from the viewer

In the mer isomer, the three similar ligands define a meridian of the octahedron. Meridian is like the imaginary circle that runs north to south (like on the earth's surface, from the North Pole to the South Pole). So in the 'mer' isomer, we start, for instance, in the plane of paper, then the 2nd similar ligand is towards you, then the 3rd similar is again in the plane of paper. Imagine going through that, you will find you just made the 'mer' of octahedron.

Like in the image, the isomer labelled mer has Cl ligands in 2 different directions (in plane of the paper and going away from you)
Similarly, in mer isomer, the ligand H2O goes in 2 different directions.

 

[Munib Ahmed]

i need help in oct/nov 2012 p41 q1b(vi)

 

[techgeek]

View attachment 62133
is there any rule for this kind of cis trans isomerism?? how to deduce the isomer structures? View attachment 62134

I have the same query. Been trying since days but I can't figure out how do we determine which is the cis and which is the trans isomer in 6 coordinate complexes and how to draw the structures??

In the 'fac' isomer, the similar ligands define the face of octahedron, which will run in 3 different directions. Like in the image, you can see one Cl ligand goes in the plane of paper, one out, towards you and the 3rd in (away from you). This makes the face of isomer.
To draw the two isomers, just draw the 'fac' isomer first, by making 3 directions and putting each same type of ligand in different direction. Then to make 'mer', just alternate one type of ligand in one direction with the other type in another direction. Like over here, you just alternate The H2O in plane of the paper with the direction towards you, which makes the H2O go in just 2 directions instead of 3 and do similarly with Cl.
There's a lot of imagination of directions required here so even if you can't do that, just remember 'fac' will have each type of ligand in 3 directions while 'mer' will have each type of ligand in 2 directions.

 

[HELLNO]

In the 'fac' isomer, the similar ligands define the face of octahedron, which will run in 3 different directions. Like in the image, you can see one Cl ligand goes in the plane of paper, one out, towards you and the 3rd in (away from you). This makes the face of isomer.
To draw the two isomers, just draw the 'fac' isomer first, by making 3 directions and putting each same type of ligand in different direction. Then to make 'mer', just alternate one type of ligand in one direction with the other type in another direction. Like over here, you just alternate The H2O in plane of the paper with the direction towards you, which makes the H2O go in just 2 directions instead of 3 and do similarly with Cl.
There's a lot of imagination of directions required here so even if you can't do that, just remember 'fac' will have each type of ligand in 3 directions while 'mer' will have each type of ligand in 2 directions.

I was writing the whole thing, and halfway through found out you did already

 

[darks]

It's called 'fac' 'mer' isomerism. Because around the metal, the 6 ligands form an octahedron which can go in 3 different different directions so form 2 different isomers.
First you need to understand that there are 3 directions and really imagine them in your head this way, when you look at the complex.
Simple line --- plane of the paper
wedges --------bonds towards the viewer
dashed --------bonds away from the viewer

In the mer isomer, the three similar ligands define a meridian of the octahedron. Meridian is like the imaginary circle that runs north to south (like on the earth's surface, from the North Pole to the South Pole). So in the 'mer' isomer, we start, for instance, in the plane of paper, then the 2nd similar ligand is towards you, then the 3rd similar is again in the plane of paper. Imagine going through that, you will find you just made the 'mer' of octahedron.
View attachment 62140
Like in the image, the isomer labelled mer has Cl ligands in 2 different directions (in plane of the paper and going away from you)
Similarly, in mer isomer, the ligand H2O goes in 2 different directions.

Thanks that helped A lot!!

 

[techgeek]

I was writing the whole thing, and halfway through found out you did already

hahahah that's okay
post yours too