Author Topic: CHEMISTRY PAPER 1 HERE  (Read 37862 times)

Offline Ghost Of Highbury

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Re: CHEMISTRY PAPER 1 HERE
« Reply #255 on: June 11, 2009, 06:32:31 pm »
ohh..tks
but in the first one i explained pereviously

the sulphur gains oxygen atoms and its oxidation state also increases..
this proves that it is oxidation

but...in the second equation the sulphur's oxidation state doesn't change...
divine intervention!

nid404

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Re: CHEMISTRY PAPER 1 HERE
« Reply #256 on: June 11, 2009, 06:38:23 pm »
ohh..tks
but in the first one i explained pereviously

the sulphur gains oxygen atoms and its oxidation state also increases..
this proves that it is oxidation

but...in the second equation the sulphur's oxidation state doesn't change...

oxidation is also the gain of oxygen atoms, which sulphur has gained.

Offline simba

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Re: CHEMISTRY PAPER 1 HERE
« Reply #257 on: June 11, 2009, 06:47:38 pm »
in question 38 june 08......

Offline Bani

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Re: CHEMISTRY PAPER 1 HERE
« Reply #258 on: June 11, 2009, 06:54:09 pm »
S has many oxidation states including -2,0,2,4,6...
in this particular reaction the oxidation state of S is "+2"
a decrease in oxidation state - reduction
an increase in oxidation state - oxidation

1.) S + O2 -> SO2
     here at the left handside, as sulphur exists itself (not compound), the oxidation state is 0
          at the right hand sidde it forms a compound and gains an oxidation state of +2 = this is oxidation
          whereas O has an oxidation state of "0" in the left hand side and decreases to -4 in the right hand side
               this is reduction

therefore its redox

Thanks a lot
+rep for you :D

nid404

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Re: CHEMISTRY PAPER 1 HERE
« Reply #259 on: June 11, 2009, 06:55:06 pm »
in question 38 june 08......

it is petroleum

Offline Bani

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Re: CHEMISTRY PAPER 1 HERE
« Reply #260 on: June 11, 2009, 06:55:16 pm »
thanks a lot everyone!
someone please try answering my previous question (M/J 2007, Q16-----the one about redox reaction) Why is the answer C?
since in equation 3 no reactants have lost or gained electrons, oxygen or hydrogen!

Ya,but why is equation 1 and 2 REDOX?
1 and 2 are only oxidation, not reduction...
please help...

it's a little difficult to explain
but i'll try...in the first one Sulphur gains oxygen atoms(oxidation) but oxygen gains electrons(reduction).
in the second one sulphur gains oxygen but oxygen gains electrons
whereas in third one although oxygen is gained, there is no transfer of electrons and hydrogen does not lose oxygen but combines with SO4
It's very difficult to explain.

* Oxygen's oxidation state reduces in the covalent bond it forms with sulphur

Thanks a lot!!!
+rep for you :D

Offline sweetsh

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Re: CHEMISTRY PAPER 1 HERE
« Reply #261 on: June 11, 2009, 06:55:22 pm »
in question 38 june 08......

C (petroleum)

Offline Petrol

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Re: CHEMISTRY PAPER 1 HERE
« Reply #262 on: June 11, 2009, 06:59:39 pm »
Can u please tell me whats the answer for May/June 2008 Question 19
Mark scheme says D.. i think its C
Cause 2KOH --> H20 thats ph going from 14 - 7 so decreases :s why is it d in the ms its wrong rite?

nid404

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Re: CHEMISTRY PAPER 1 HERE
« Reply #263 on: June 11, 2009, 07:03:09 pm »
Can u please tell me whats the answer for May/June 2008 Question 19
Mark scheme says D.. i think its C
Cause 2KOH --> H20 thats ph going from 14 - 7 so decreases :s why is it d in the ms its wrong rite?
There is excess KOH
pH of water increases from 7 to 13/14
« Last Edit: June 11, 2009, 07:05:16 pm by nid404 »

Offline Petrol

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Re: CHEMISTRY PAPER 1 HERE
« Reply #264 on: June 11, 2009, 07:11:09 pm »
can u explain further ... and please are u 100%?

nid404

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Re: CHEMISTRY PAPER 1 HERE
« Reply #265 on: June 11, 2009, 07:14:03 pm »
can u explain further ... and please are u 100%?

yes im 100% sure. See when the two react, KOH is in excess..it still remains in the solution after the reaction is over. The pH of the solution increases as the alkali is in excess. I've tried my best to explain it.

Offline girl_92

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Re: CHEMISTRY PAPER 1 HERE
« Reply #266 on: June 11, 2009, 07:18:08 pm »
can u explain further ... and please are u 100%?

yes im 100% sure. See when the two react, KOH is in excess..it still remains in the solution after the reaction is over. The pH of the solution increases as the alkali is in excess. I've tried my best to explain it.
luk man der is no other possibility by which the pH can increase so its simple tht KOH is in excess
some people sleep to dream while othrs wakeup to follow dem im the second type how abt u

Offline igexam

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Re: CHEMISTRY PAPER 1 HERE
« Reply #267 on: June 11, 2009, 07:26:27 pm »
Could someone help me with question 20 in november 2008. I don't understand y ph should increase...

Offline girl_92

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Re: CHEMISTRY PAPER 1 HERE
« Reply #268 on: June 11, 2009, 07:30:55 pm »
Could someone help me with question 20 in november 2008. I don't understand y ph should increase...
hcl is uesd up na so the pH will increase
some people sleep to dream while othrs wakeup to follow dem im the second type how abt u

Offline Triple_A

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Re: CHEMISTRY PAPER 1 HERE
« Reply #269 on: June 11, 2009, 07:32:38 pm »
Nope......pH will decrease (acidic) bec nitric acid forms!
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