Chemistry: Post your doubts here!

[Rizwan Javed]

View attachment 59902
How do I know which one is a redox reaction? (Ans is B)

Option A shows a simple dehydration or elimination reaction. No change in oxidation takes places.

Option C is the hydrolysis of esters. Again no change in oxidation states.

Option D: The reaction does not take place, as ketones do not react with fehling's solution.

Only Option B shows a redox reaction as in this reaction the aldehyde is oxidised to form carboylic acid, and the Ag+1 ions present in the tollen's reagent are reduced to form Ag(s). So as both oxidation and reduction take place, this is the only redox reaction.

 

[The Sarcastic Retard]

Most common oxidation state is +2 but the transition elements at the start of the row oxidation state involves all of the electrons present in the 4s and 3d subshells , however from iron onwards the maximum oxidation state becomes +2 since the 3d electrons become relatively harder to remove. for example vanadium which is a transition element at the start of the row can have all of its electrons removed from the 4s and 3d subshell therefore can be +1 . +2 , +3 , +4 and even +5. I might be mistaken correct me if i'm wrong though.

Ty. I d k if u are wrong coz I have got nothing to be frank.

 

[The Sarcastic Retard]

sfhn_128 Here you go

Do you have for A level?

 

[cute97]

Do you have for A level?

No, am so sorry!

 

[The Sarcastic Retard]

No, am so sorry!

no problem. ^_^

 

[holoholo]

Can someone please give me a description on how to do this ?

 

[qwertypoiu]

View attachment 59904

Can someone please give me a description on how to do this ?

Take a measuring cylinder. Place it on a balance. Zero the balance. Add distilled water to the measuring cylinder until 30g of water has been poured. Now zero the balance again. Add KCl solid, carefully, so that 2.238g are added. This means you added 0.03mol of KCl.
The molality of this solution (stir it) will be 1mol/kg. Lets call this your Ultra Solution (US)
Now we will do serial dilution.
Take five more measuring cylinders. Add 0g of distilled water to first, 2g to second, 4g to third, 6g to fourth, and 8g to fifth.
Now take your Ultra Solution and add 10g of it to first, 8g to second, 6g to third, 4g to fourth, and 2g to fifth.
Stir them all.
Note that we've used 50g of distilled water so far.
Your first cylinder has molality 1.0mol/kg
Second one is 0.8mol/kg
Fourth is 0.4mol/kg
Last one is 0.2mol/kg

Use the remaining water to clean your apparatus
Nah just kidding you could use it to repeat your experiment or just make larger volumes of the above solutions.

 

[silver slick]

interpret and explain qualitatively the variation in solubility of the
hydroxides and sulfates in terms of relative magnitudes of the
enthalpy change of hydration and the corresponding lattice energy

any notes or explantion? Please HELP

 

[Qaussain]

Option A shows a simple dehydration or elimination reaction. No change in oxidation takes places.

Option C is the hydrolysis of esters. Again no change in oxidation states.

Option D: The reaction does not take place, as ketones do not react with fehling's solution.

Only Option B shows a redox reaction as in this reaction the aldehyde is oxidised to form carboylic acid, and the Ag+1 ions present in the tollen's reagent are reduced to form Ag(s). So as both oxidation and reduction take place, this is the only redox reaction.

agreed with ur statement

 

[shahzaib9291]

Is there a possibility that i can score a B or C in A level after having a D in As level?

 

[holoholo]

Take a measuring cylinder. Place it on a balance. Zero the balance. Add distilled water to be measuring cylinder until 20g of water has been poured. Now zero the balance again. Add KCl solid, carefully, so that 1.492g are added. This means you added 0.02mol of KCl.
The molality of this solution (stir it) will be 1mol/kg. Lets call this your Ultra Solution (US)
Now we will do serial dilution.
Take five more measuring cylinders. Add 0g of distilled water to first, 2g to second, 4g to third, 6g to fourth, and 8g to fifth.
Now take your Ultra Solution and add 10g of it to first, 8g to second, 6g to third, 4g to fourth, and 2g to fifth.
Stir them all.
Note that we've used 40g of distilled water so far.
Your first cylinder has molality 1.0mol/kg
Second one is 0.8mol/kg
Fourth is 0.4mol/kg
Last one is 0.2mol/kg

Use the remaining water to clean your apparatus
Nah just kidding you could use it to repeat your experiment or just make larger volumes of the above solutions.

You added a total of 10+8+6+4+2 which is 30 g but you only made 20 g ?

 

[qwertypoiu]

You added a total of 10+8+6+4+2 which is 30 g but you only made 20 g ?

Oops sorry yes that's a mistake I'll edit it in a minute

 

[qwertypoiu]

interpret and explain qualitatively the variation in solubility of the
hydroxides and sulfates in terms of relative magnitudes of the
enthalpy change of hydration and the corresponding lattice energy

any notes or explantion? Please HELP

You're looking for 10.1(g)

 

[The Sarcastic Retard]

Is there a possibility that i can score a B or C in A level after having a D in As level?

Depends, what percentage did u get?
If its low D then it can hardly go to C if its high D then more chance to get a C and little more hard work can fetch u B as well! ^_^

 

[silver slick]

You're looking for 10.1(g)

thank you so much!!!

 

[Saad the Paki]

So is there a way to tell whether carbon atoms in a ring (or any molecule) lie in a plane?

 

[qwertypoiu]

So is there a way to tell whether carbon atoms in a ring (or any molecule) lie in a plane?View attachment 59908

To see if atoms lie in a plane, we have to think of the type of bonding and the shape it would have.
If the atoms form a part of trigonal planar structure, then of course it's planar. Same goes for C atoms in a benzene ring. Also ethene (because of C=C bond) is planar I think.

In your particular question, most of the carbon atoms involved have undergone sp3 hybridisation and thus are involved in tetrahedral arrangements. There is no way they could all lie on one single plane.

 

[ashcull14]

is iodoform test included in organic chemistry 2016 course?

 

[My Name]

is iodoform test included in organic chemistry 2016 course?

It is there for the AS part.
So if you're doing AS or AL then you need to know it.


http://www.cie.org.uk/images/164502-2016-2018-syllabus.pdf

A Level material moved to AS material
10.4 (c) deduce the presence of a CH3CH(OH)– group in an alcohol from its reaction with alkaline aqueous iodine to form tri-iodomethane 10.5 (e) describe the reaction of CH3CO– compounds with alkaline aqueous iodine to give tri-iodomethane

 

[ashcull14]

It is there for the AS part.
So if you're doing AS or AL then you need to know it.


http://www.cie.org.uk/images/164502-2016-2018-syllabus.pdf

A Level material moved to AS material
10.4 (c) deduce the presence of a CH3CH(OH)– group in an alcohol from its reaction with alkaline aqueous iodine to form tri-iodomethane 10.5 (e) describe the reaction of CH3CO– compounds with alkaline aqueous iodine to give tri-iodomethane

oh thank u so much