Chemistry Doubts: IGCSE Paper 3

[ThatReallyReallyWeirdDude]

Is Naphta used for a fuel or just for heating systems? And which fraction exactly does it come out from? The book says nothing about it!

He's right.
Sorry for being late, was asleep
Just know the order of the fractions, their uses and that the boiling point increases as length of carbon chain increases (and why)

 

[Dsilentkila]

ei brodas.
lil help.
Can some one pls differentiate between structural formulas and normal formulas ( in organic chemistry)
i really dont now what to do in Draw/ write structural formualas.
thankies in advance

 

[ThatReallyReallyWeirdDude]

ei brodas.
lil help.
Can some one pls differentiate between structural formulas and normal formulas ( in organic chemistry)
i really dont now what to do in Draw/ write structural formualas.
thankies in advance

Alright the difference is that structural actually shows the positioning/structure of the atoms
Now the first thing you do when drawing structural formulas is draw the skeleton of carbon atoms.
For example lets say they tell you to draw pent-2-ene
We know three things as soon as they tell us pent-2-ene
a) It has a formula of C5H10
b) The double bond is located after the second carbon atom (hence the 2)
c) It has 5 carbon atoms
SO first thing you do is draw the carbon atoms since they form like the main structure
in this case it is:
C-C=C-C-C
Then you have to remember; carbon atoms can form four bonds, so you have to fill whatever bonds that are not filled!
The first carbon atom only has one bond, so add three hydrogens
The second carbon atom has three bonds, so add one hydrogen
The third carbon atom also has three bonds so add one hydrogen
The fourth carbon atom has 2 bonds so add two hydrogens.
The last carbon atom has 1 bond so add 3 hydrogens.

The end result is this:


In general you can apply this anywhere. If they said to draw 1,3 dichloropentane, you know there is 2 chlorines and that they are located on the first and third carbon atom. You have to understand what the numbers mean so you can put things such as hydroxyl groups, halogens and double bonds in the right place.

 

[Besterlinks]

Guys, help me with this question. Thanks.




The same linkage is found in polyesters. Draw the structure of the polyester which can be formed from the monomers shown below.

HOOC—C6H4—COOH andHO—CH2 —CH2 —OH

 

[Maz]

This is condensation polymerisation. So, water is removed from it.

HOOC - C6H4 - CO - CH2 - CH2 - OH

 

[salvatore]

Hey.. I don't understand how cathodic protection of iron/steel works. My text book says that the iron/steel should be the anode.. but here, http://en.wikipedia.org/wiki/Cathodic_protection it says that it should be the cathode. Could someone please explain that + how the cathodic protection works. Thanks

 

[ThatReallyReallyWeirdDude]

Let me show you guys something:

And if you search the syllabus with the find function the word cathodic doesn't appear once.
Learn it if you want; don't take my word for it, but it's not there on syllabus, unless it's counted as some sort of subsection of sacrificial protection.

 

[salvatore]

Hehe yeah.. but CIE is quite unpredictable! Check dis out; qn. 5 (b).. http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s07_qp_3.pdf

 

[Jspake]

I'm getting confused on how to draw an ionic bond.. http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w08_qp_03.pdf Qn. 2 (a).. could you please draw it for me. I'll really appreciate it.. Thanks!

 

[Maz]

You know I don't think we have to learn cathodic protection as a separate topic altogether. Instead , weshould apply the knowledge we already have (Electrolysis and sacrificial protection)

 

[ZainH]

I'm getting confused on how to draw an ionic bond.. http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w08_qp_03.pdf Qn. 2 (a).. could you please draw it for me. I'll really appreciate it.. Thanks!

Just made this on paint, hope it helps!

 

[saroooor]

This is condensation polymerisation. So, water is removed from it.

HOOC - C6H4 - CO - CH2 - CH2 - OH

I believe you should Remove the oh at the end right side and the H a the other end left side . Also in between it is COO ? I Believe so ...?!

 

[areebaization]

Hehe yeah.. but CIE is quite unpredictable! Check dis out; qn. 5 (b).. http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s07_qp_3.pdf

it is possible that CP was in the 2007 syllabus and so it was asked ...but it is always better to do more

 

[Jspake]

Just made this on paint, hope it helps!

Thanks a lot bro!

 

[salvatore]

it is possible that CP was in the 2007 syllabus and so it was asked ...but it is always better to do more

Yeah.. that's possible. But.. prevention is better than cure!

 

[Maz]

I believe you should Remove the oh at the end right side and the H a the other end left side . Also in between it is COO ? I Believe so ...?!

Oh,right. Thnx.

-OOC - C6H4 - COO - CH2 - CH2 -

 

[ThatReallyReallyWeirdDude]

Hehe yeah.. but CIE is quite unpredictable! Check dis out; qn. 5 (b).. http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s07_qp_3.pdf

That's 2007. If you open the 2007 syllabus it will say, "Understand cathodic protection blah blah blah."

 

[Maz]

Yeah.. that's possible. But.. prevention is better than cure!

As far as i have seen cathodic protection is the same as what we already have in our syllabus. Namely - Electrolysis and sacrifial protection.

 

[saroooor]

Oh,right. Thnx.

-OOC - C6H4 - COO - CH2 - CH2 -

Did you check the mark scheme ,for that ?

 

[Maz]

That's 2007. If you open the 2007 syllabus it will say, "Understand cathodic protection blah blah blah."

By the way it doesn't.