IG Chemistry Paper 3 discussion

[nid404]

bromine? How many different variants were there?
well..it depends on the mole ratio..
for example, in my paper, it was 0.08 moles of silicon reacts with 7.2g of fluorine, the equation given was

Si  +  2F₂  ----> SiF₄

so, silicon and fluorine are in the mole ratio 1:2
the moles of fluorine given is 7.2/(19x2) = 7.2/38 = 0.189 moles....(we use 38, cuz its diatomic, so we take double the original A_r

so that means, if fluorine is 0.189 moles, then according to the mole ratio, silicon should be 0.189/2 = 0.095 moles...but it is 0.08..meaning, silicon is limiting..

I took the mole ratio(1:2)
so if silicon was 0.08 then fluorine needed was 0.16(0.08x2) which is 0.16x38g(6.08g)
but there was 7.2g, much more than required ans so silicon limiting reagent

different approach but yeah same ans

[LoCo93]

yeah loco.. I rote silion too... itt had the least amount of moles...

ROCK ON!!! =] 

[crypsAnity]

ahahaha.. yeah n i found that flourine was in excess.. n i knew ahd to rite the oppsite of what i find in excess.. but nawwsss had to be me n rote flourinee! yayyyy .. sighs ..

[LoCo93]

i rote sumthin like add a magneisum (or any metal) ribbon and if its acidic it'll react..  dont kno tho..

But GUYS.... the question asked how you could determine the compounds contained the same COOH group!! Just because it reacts with a base or a carbonate wont tell that its a COOH group.

naa m tlkin abt the one with tells us how do u tell if its an acid.. <3 i gues ther was a different one either that or i totali screwd up  

[crypsAnity]

errr.. hold on a sec.. there was no question as far as i can remember which wanted to know if it COOH group.. what this? .. it asked about how would u determine ts an acid.. hmmm if thts wht ur talkign abt..

[bibo the wa7sh]

what i think was that the value of the height had nothing to do with the volume, since height was in mm, and volume in cm³. I just remember that, 18 cm³ of aqueous nitrate of T, reacted with 2 cm³ portions of a solution of Na₃PO₄. The maximum precipitate of the phosphate of T, was reached at 6 cm³ of sodium phosphate. Since both had the same concentration, it didnt really matter, the main thing that mattered was the volume then. Now, we have that the volume of the nitrate of T used was 18, and that of the sodium phosphate was 6. so volume ratio of the nitrate reactant to the phosphate reactant is 18:6 = 3:1, which is also the mole ratio. So if we construct an ionic equation using the mole ratio, we can get ...

PO₄^3-  +  3T⁺  ---->  T₃PO₄

when i came home, i opened june 2004 paper 3, of chem, where i remember seeing a similar graph as the one given in the question..

in the june 2004 q, 4 cm³ of aqueous iron (III) chloride, reacts with 2cm^3 portions of aqueous sodium hydroxide..according to the graph..the maximum volume of sodium hydroxide at which the maximum precipitate is formed, is at 12 cm^3..

thus the volume ratio of the chloride reactant to the hydroxide, is 4:12 = 1:3
That means, there will be one Fe³⁺ ion for every 3 OH^- ions..according to the ratio..

the next part of the given is..complete the following reaction..

Fe³⁺   +   .....OH^-  -----> ...........

since ratio is 1:3..itll be 3 OH^- forms Fe(OH)₂..
the concentration of both reactants is 1moldm^-3 which is given..

so the questions are quite similar..and so, i think T₃PO₄

i dont consider myself a genius, just mixxing familiar stuff with unfamiliar stuff.

Dude I love You!!
I used exact same reasoning!!!!!
Atleast now i know i used valid reasoning!!
Thank you!

I Wote the same thing exactly in ma test ,this is SupeRb!!!

[aquarian93]

u guys for the aq. NaCl question, im scared, i rote H2 at cathode and Cl2 at anode,  bt some ppl are saying its O2 at anode.

anyone noes da boundary for an A?

the paper was too long

[LoCo93]

errr.. hold on a sec.. there was no question as far as i can remember which wanted to know if it COOH group.. what this? .. it asked about how would u determine ts an acid.. hmmm if thts wht ur talkign abt..

yea cryps.. thats wht m tlkin abt.. =]

[Shogun]

yea u add any metal carbonates if it fizzes due to liberation of carbondioxide, then its an acid..