Chem Paper1

[Jezla]

Somebody plz tell me why the answer for the 22nd Q is B
And Yeah, here's the link,

http://www.xtremepapers.net/CIE/Cambrid ... 4_qp_1.pdf

 

[Zishi]

Because 1, 3 and 4 are not typical properties of a oxidizing agent. So, 2 is the answer, but as it comes with 1 in B part, that's why the answer should be B.

 

[jafar]

potassium iodide is a reducing agent and when its oxidised it changes color from colourless to red/brown, only in 1 and 2 is its color changing, so it means that solutions 1 and 2 contain oxidising agents whih oxidise KI...
now do u understand

 

[Jezla]

But isn't Potassium Manganate an oxidising agent?????

 

[Zohaib Sherazi]

Don't get distracted by the presence of potassium manganate. The fact that potassium iodide changes colour in solutions 1 and 2 proves that there must be an oxidising agent present.

 

[jafar]

yeah it is bt it dosent oxidise,
A reducing agent always oxidises nd an oxidising agent always reduces!!!

 

[Jezla]

Yeah BUT in 1 and 3 the colour of Potassium Manganate too changes!!!!!!!!!

 

[jafar]

this means that 1 and 3 contain reducing agents, but as zohaib said u should ignore that as u r only asked about oxidising agents and by mixing potassium iodide u noe dat 1 and 2 contain oxidising agents, so oxidising agents will be 1 & 2, understand??

 

[Jezla]

Ryt i just deleted that understood post!! 'coz iv got another doubt..
in 1 y does potassium manganate change color with an oxidising agent?

 

[jafar]

b/c it could both be reduced and oxidised,
for example,
Fe 2+ can oxidise and form Fe 3+
Fe 2+ can reduce and form Fe (Iron),

this is such an ezy question, much more trickier questions can cum in xam, u shud study hard!!

 

[Jezla]

True, but does it apply to Potassium Manganate too? Together with the color change????

 

[jafar]

what apply to potassium manganate??

 

[Jezla]

umm the thing about Fe both reducing and oxidizing??????

 

[jafar]

only Transition metals have various oxidation states
thats why they have different names such as Fe(III), Fe(II), Cu(II)

 

[Jezla]

OMG!! u ddnt get it did you?
You just compared Potassium Manganate to Fe, thats y I asked if Potassium Manganate cud oxidise as well as reduce!!!
Anyways the thing about transition metals having varying oxidation states- I already knew Thanks though!!

 

[jafar]

what do u mean i ddnt get it?? :S, i answered ur question

 

[Jezla]

Tz alryt, drop it thankz for answering my Q........
I'll get my doubt cleared from one of my friendz.
Thanks Loadz anyways..

 

[jafar]

i was tryn 2 say dat only transition elements can both oxidise and reduce as they hav various oxidation states,!! wats rong in this??

 

[Jezla]

You are ryt of course!!
But does Potassium Manganate too oxidise and reduce lyk Fe?

 

[jafar]

no it dozent, although Mangnese is also a a Transition metal but in Potassium Manganate (KMnO4) its bonded with Potassium and Oxygen.... so it only has 1 oxidation state and thus it only reduces,!!!

i m really sorry if u felt bad for what i said, i should'nt have said dat as it wasent my business, sorry again