Chemistry: Post your doubts here!

[Metanoia]

Balancing the equation!

Just balance key element first then O and then H.

An alternative would be to realize that the half equations are in the data booklet

Fe2+ --> Fe3+ + e ---(1)

MnO4- + 8H+ + 5e --> Mn2+ + 8H2O ---- (2)

We simply need to multiply eqn (1) by 5 before adding to eqn (2)

 

[Metanoia]

Does anyone know about Partition Coefficient? How do we know which one substance is at the top and which is at the bottom?

Look at the density, the denser liquid would be at the bottom.

 

[Midnight dream]

Yes. Cis isomers would be very unlikely in small rings (less than 8 carbons) due to the strain on the bonds.

Thanks
But the question had 17 carbons in it...Shouldn't it then display cis trans....The answer said no..

 

[Metanoia]

Thanks
But the question had 17 carbons in it...Shouldn't it then display cis trans....The answer said no..

Its not about the total number of carbons. Its about the number of carbons within a ring.

For that question, if i remember correctly, the number of carbons in the rings are either five or six.

 

[Midnight dream]

Its not about the total number of carbons. Its about the number of carbons within a ring.

Thank you soo much..

 

[Studydayandnight]

Guys please help!!

I don't understand how to answer the questions (c) (iii), d(i), d(ii) .

How does the reaction show that it's a carboxylic acid? How do we identify it as ethanoic acid?

I've attached the mark scheme as well!

http://freeexampapers.com/A-Level/Chemistry/CIE/2013-Jun/9701_s13_ms_22.pdf

 

[My Name]

Guys please help!!

I don't understand how to answer the questions (c) (iii), d(i), d(ii) .

How does the reaction show that it's a carboxylic acid? How do we identify it as ethanoic acid?

I've attached the mark scheme as well!

http://freeexampapers.com/A-Level/Chemistry/CIE/2013-Jun/9701_s13_ms_22.pdf

For part c iii
in the question they mention
A third sample of R gave an effervescence with sodium carbonate
so it has to be carboxylic acid ! ( since no other functional group would give effervescence)

for the next part d i
refer to this post
https://www.xtremepapers.com/commun...st-your-doubts-here.9859/page-600#post-896183
Credits to Metanoia for that ^

 

[shaeer999]

w2014 qp 11. ans= A, how is it done??

 

[My Name]

View attachment 52496 w2014 qp 11. ans= A, how is it done??

Refer to this post:
https://www.xtremepapers.com/commun...st-your-doubts-here.9859/page-602#post-896283

 

[Studydayandnight]

I need more help! :/

For (a) (ii) I just wanted to confirm that we know it's carboxylic because CO2 is given out and there'll be effervescence?

Can someone please explain part (b) to me?

Here's the mark scheme.

http://freeexampapers.com/A-Level/Chemistry/CIE/2012-Jun/9701_s12_ms_23.pdf

 

[asadalam]

I need more help! :/

For (a) (ii) I just wanted to confirm that we know it's carboxylic because CO2 is given out and there'll be effervescence?

Can someone please explain part (b) to me?

Here's the mark scheme.

http://freeexampapers.com/A-Level/Chemistry/CIE/2012-Jun/9701_s12_ms_23.pdf

Ok,so just a little something to keep in mind if it says heat with conc H2so4 its most likely a dehydration reaction,or elimination.The formula of H can be deduced as dehydration takes out the OH and H bonded with one of the C the structural formula that i came up with was CH2(OH)CH2C02H you can draw that on paper to be sure.The h2so4 will take out the H and OH and cause to form a double bond with 2 C atoms in between( not the CO2H one),which will be oxidised by cold dilute kmno4 to make it colorless,and form a diol with both C=C getting a an OH bond.


Practice more and more organic and eventually you'll get a hang of this.

 

[Studydayandnight]

Ok,so just a little something to keep in mind if it says heat with conc H2so4 its most likely a dehydration reaction,or elimination.The formula of H can be deduced as dehydration takes out the OH and H bonded with one of the C the structural formula that i came up with was CH2(OH)CH2C02H you can draw that on paper to be sure.The h2so4 will take out the H and OH and cause to form a double bond with 2 C atoms in between( not the CO2H one),which will be oxidised by cold dilute kmno4 to make it colorless,and form a diol with both C=C getting a an OH bond.


Practice more and more organic and eventually you'll get a hang of this.

CH2=CHCO2H , this is the answer from the markscheme. It has no OH group present. :/

 

[ahmedish]

Which part in the syllabus does it have the bit where AgCl or AgBr react with NH3 to give Ag(NH3)2Br?? I have found it twice in the past papers (old though like 2004 and 2006)

 

[Studydayandnight]

5 (c) http://freeexampapers.com/A-Level/Chemistry/CIE/2012-Jun/9701_s12_ms_23.pdf

May/June/2012

Variant 23

I've attached the mark scheme! Please help guys, this question alone carries 4 marks :/

 

[Suchal Riaz]

5 (c) http://freeexampapers.com/A-Level/Chemistry/CIE/2012-Jun/9701_s12_ms_23.pdf

May/June/2012

Variant 23

I've attached the mark scheme! Please help guys, this question alone carries 4 marks :/

I'll start from begining If you will.
Only COOH reacts with carbonates so it has COOH group
SO by the information we have we can deduce structure of F
it has COOH, rest of it is C2H5O. if its has OH it will be CH3CH(OH)COOH. That fits all the information.
The type of reaction has to be oxidation because KMnO4 is an oxidising agent.
When H is treated with conc. H2SO4 it will be a dehydration reaction. So it will become CH2=CHCOOH. when oxidised with cold KMnO4 it becomes CH2(OH)CH(OH)COOH.

SO we have two groups in F that will react with Na. OH and COOH.
so one mole of F will react with 2 mol of Na to produce 2 H which is actually 2/2 H2 or 1 H2
That means that n(F)=n(H2).
n(F)=0.6/Mr and Mr=3(12)+6+3(16)=90
n(F)=0.006667 mol = n(H2)
volume = n*24 dm3 = 0.006667*24=0.16 dm3=160cm3


If anything is not clear feel free to ask without any hesitation.

 

[asadalam]

CH2=CHCO2H , this is the answer from the markscheme. It has no OH group present. :/

I was talking about the original,un-dehydrated molecule if you will.After dehydration the OH and H will be removed and you'll get the structure given in the ms.

 

[Midnight dream]

If a carbon has 4 different groups attached to,would it exhibit cis-trans isomerism?

For e.g. 2 bromo,2 hydroxy,1 methyl ethene ? Would this exhibit cis trans ??
Metanoia Please answer this query..

 

[Metanoia]

If a carbon has 4 different groups attached to,would it exhibit cis-trans isomerism?

For e.g. 2 bromo,2 hydroxy,1 methyl ethene ? Would this exhibit cis trans ??
Metanoia Please answer this query..

Short answer would be no, it would not exhibit cis-trans. The type of isomerism for 4 different groups would be E-Z isomers (entgegen zusammen).

http://www.chemguide.co.uk/basicorg/isomerism/ez.html

 

[Metanoia]

View attachment 52496 w2014 qp 11. ans= A, how is it done??

There is actually no need to calculate moles or use gas constant, since both values are the same before and after the change.

 

[Midnight dream]

Short answer would be no, it would not exhibit cis-trans. The type of isomerism for 4 different groups would be E-Z isomers (entgegen zusammen).

http://www.chemguide.co.uk/basicorg/isomerism/ez.html

Thankyou.