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Chemistry: Post your doubts here!

itallion stallion

itallion stallion

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A star said:
its usually common sense you have too apply in this one its common knowledge the NH4+ has a dative covalent bond (H atom donates to Cl-. in others for example CO you have no choice but to draw a simple double bond it would be accepted (mind you the structure is abit different in reality but not needed by cie) and try t see if the valency is being satisfied or not
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Do u have any examples of compound which have coordinate bond,double bond etc along with their structure!thanks
 
itallion stallion

itallion stallion

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abruzzi said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_41.pdf
Please help me with qn no. 5b(iii). How do you know the structure?
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Read the details given in the question for the compound.
It says it gives white ppt with Br2 aq means it will have a phenol.gives yellow ppt with tri idoform test means there will be COCH3 group present and it is mentioned that it is 1,4 di substituted.so phenol at 1 and COCH3 at 4.got it!
 
Aaquib Khalid

Aaquib Khalid

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Could anyone tell me how to calculate the number of carbons present in the mass spectra when the relative height of the M and M+1 peaks are given as 9 and 0.3? And also how does when the abundance has been given in place of relative height?
 
Jelleh Belleh

Jelleh Belleh

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A

A star

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itallion stallion said:
I can't relate the cathode equation with overall Eo.u must be having the same problem!
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nope i got that . i know the problem but am ignoring it for the sake of getting the paper done . the overall Eo value is not the same as that of a lead-acid battery. what i caannot get is the last part shouldnt the the over E0 change be O
 
abruzzi

abruzzi

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itallion stallion said:
Read the details given in the question for the compound.
It says it gives white ppt with Br2 aq means it will have a phenol.gives yellow ppt with tri idoform test means there will be COCH3 group present and it is mentioned that it is 1,4 di substituted.so phenol at 1 and COCH3 at 4.got it!
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so it was that simple huh. thanks a tonne :)
 
H

hope4thebest

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Farez said:
We need to look at the bonding in the -CONH2 group.

Like any other double bond, a carbon-oxygen double bond is made up of two different parts. One electron pair is found on the line between the two nuclei - this is known as a sigma bond. The other electron pair is found above and below the plane of the molecule in a pi bond.

A pi bond is made by sideways overlap between p orbitals on the carbon and the oxygen.

In an amide, the lone pair on the nitrogen atom ends up almost parallel to these p orbitals, and overlaps with them as they form the pi bond.

image: http://www.chemguide.co.uk/organicprops/amides/amidedeloc.gif

The result of this is that the nitrogen lone pair becomes delocalised - in other words it is no longer found located on the nitrogen atom, but the electrons from it are spread out over the whole of that part of the molecule.

This has two effects which prevent the lone pair accepting hydrogen ions and acting as a base:
  • Because the lone pair is no longer located on a single atom as an intensely negative region of space, it isn't anything like as attractive for a nearby hydrogen ion.
  • Delocalisation makes molecules more stable. For the nitrogen to reclaim its lone pair and join to a hydrogen ion, the delocalisation would have to be broken, and that will cost energy.


Compare E values of the metal getting reduced at the cathode with that of H2 (which is zero). So if it's positive, the metal gets discharged. If negative, hydrogen gets discharged.

Ag+ + e– ⇌ Ag E = +0.80 so Ag discharged
Fe2+ + 2e– ⇌ Fe E = –0.44 so H2 discharged
Mg2+ + 2e– ⇌ Mg E = –2.38 so H2 discharged

Compare E values of the anion with that of
O2 + 4H+ + 4e– ⇌ 2H2O E = +1.23

F2 + 2e– ⇌ 2F– E = +2.87 more positive so O2 discharged
S2O82– + 2e– ⇌ 2SO42– E = +2.01 more positive so O2 discharged
Br2 + 2e– ⇌ 2Br– E = +1.07 less positive so Br2 discharged
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Thank You so much brother but dont we consider this equation= O2+2H2O+4e- ⇌ 4OH- (E=+0.40 V) for the anode reactions?
 
SOTZAIDI

SOTZAIDI

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I just want to know one answer ... for now ;D ..... thst in question paper they ask for structural formulae but in mark scheme they draw skeletal, do we have to draw skeletal or we can simply write structural formulae in draw structures question?? this is for Paper 4 a2 structured que
 
H

hope4thebest

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SOTZAIDI said:
I just want to know one answer ... for now ;D ..... thst in question paper they ask for structural formulae but in mark scheme they draw skeletal, do we have to draw skeletal or we can simply write structural formulae in draw structures question??
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Its perfectly fine with structural formula but not displayed of course.
 
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