IG Chemistry Paper 3 discussion

[horror]

it wasnt OH in tht fe thing it was some halogen i think, im100% sure it wasnt OH in the fill in the blanks stuff for tht ionic reaction. however ure explaination is good.

Trust me man K2PO4 is right otherwise my teacher and a couple of A* students are wrong it was a tough question though xD

[bibo the wa7sh]

heY everYone,
wat about electrolysis of dilute sodium chloride???
Cathode..........
anode..............
and wat happens to the electrolyte???.....
WaiTinG 4 uR RepLies!!xD!!

at da cathode it was h₂
at anode it was o₂
so conc. NaCl was left

NOPE its was concentrated NaCl
therefore @ anode Cl would be depsoed no O2

um totally sure it was DILUTE aqueos sodium chloride because i saw the test after we did it by 1 day(24 hours!!) from our teacher in sKewL!!!xD!!

[Shogun]

heY everYone,
wat about electrolysis of dilute sodium chloride???
Cathode..........
anode..............
and wat happens to the electrolyte???.....
WaiTinG 4 uR RepLies!!xD!!

at da cathode it was h₂
at anode it was o₂
so conc. NaCl was left

NOPE its was concentrated NaCl
therefore @ anode Cl would be depsoed no O2

um totally sure it was DILUTE aqueos sodium chloride because i saw the test after we did it by 1 day(24 hours!!) from our teacher in sKewL!!!xD!!

yup it was dilute..

[Kim243]

Guys there are a few questions i wanted to make sure that they are correct
1-heat the solution--> i wrote to seperate crystals from water
2-what type of organic compound has the following linkage--->polyester
3-the complete question an alchohol group and an acid group (didnt write organic before acid:/)
4-advantages -->biodegradable so it wont cause pollution
5-water behaves as a base-->cuz its a proton acceptor
6- for the equation between sodium flouride and calcium chloride why was double the volume of NaF added?-->i wrote cuz 1 mole of CaCl2 reacts with 2 moles of NaF
7-condensation or addition? condensation cuz water was removed from the monomer
8-the stronger acid was HCl cuz it was 97% ionized
9-ph of HCl will be lower than the other acid (Or do i have to write values)?
10-for the raw materials i wrote -->fractional distillation of liquified air and cracking of an alkane (didnt notice that the process wasnt required)
11-the moles 0.07 same as silicon?and could somebody plz explain which one is limiting and why?
12-for the T formula i got the formula wrong but i wrote the volume of phosphate solution is double the volume of metal T nitrate solution for the explanation
13-for the exothermic reaction i got the values of reactants and products and checked which has greater value
I know the q's are too many but im kinda freaked out cuz i did very badly in the exam

[robot_avenger]

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!

[zara]

Guys there are a few questions i wanted to make sure that they are correct
1-heat the solution--> i wrote to seperate crystals from water
2-what type of organic compound has the following linkage--->polyester
3-the complete question an alchohol group and an acid group (didnt write organic before acid:/)
4-advantages -->biodegradable so it wont cause pollution
5-water behaves as a base-->cuz its a proton acceptor
6- for the equation between sodium flouride and calcium chloride why was double the volume of NaF added?-->i wrote cuz 1 mole of CaCl2 reacts with 2 moles of NaF
7-condensation or addition? condensation cuz water was removed from the monomer
8-the stronger acid was HCl cuz it was 97% ionized
9-ph of HCl will be lower than the other acid (Or do i have to write values)?
10-for the raw materials i wrote -->fractional distillation of liquified air and cracking of an alkane (didnt notice that the process wasnt required)
11-the moles 0.07 same as silicon?and could somebody plz explain which one is limiting and why?
12-for the T formula i got the formula wrong but i wrote the volume of phosphate solution is double the volume of metal T nitrate solution for the explanation
13-for the exothermic reaction i got the values of reactants and products and checked which has greater value
I know the q's are too many but im kinda freaked out cuz i did very badly in the exam

1.to remove all the water
2.polyester
3.dont remember the ques
4.correct but they asked for two so u had to rite one more.
5.correct
6.dont remember if it came.
7.correct
8.dont remember the ques well..
9.even this one>>dont remember..
10.liquid air and methane
11.0.08>>same as silicon
12.i got this rong
13.dont remember the ques..

[Kim243]

yay so the polyester one is right!!...but for silicon how come is it 0.08 i remember the ques was 0.07 moles of silicon reacted with 25 g of bromine O.o??maybe there were some differences in the exam...any more feedback?

[zara]

well...different variant...well if silicon in ur ppr was 0.07 den the product will also be the same as dat of the limiting reagent.....n if in ur ppr it was COO...the linkage i mean well den its polytester...

[Kim243]

yeah cuz some ppl kept sayin its ester or fats it didnt make any sense to me....anyone else? feedback?

[....]

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!

well..in my paper..i just wrote the formula, the first thing in my answer..then i made it clear the two volumes of the solution, then somehow i got a balanced symbol equation and wrote it down, and wrote after it..tht above is the chemical equation, according to the volume and mole ratios..hope thts an explanation that'll suffice

[matt skywalker]

1.right
2.i think it's fats
3.i wrote alcohol and carboxylic acid
4. right
5.right
6. in variant 2 the q was diff. but your answer is right
7.right
8. right
9. i think you had to write values as well
10.umm..maybe its right, but i think a mark will be deducted for not writing raw materials because that was the next part
11. right. silicon was the limiting reagent because it had less moles than fluorine in the ratio 1:1
12. t3po4 i think, but maybe its diff. in other variants
13. right
all of my friends were saying theirs were bad too, so i think the a threshhold will be low (i hope so anyway because it was wayy too difficult and long). I hope it helps. But i'm glad the table from the study guide came, i was memorising it like crazy half an hour before

[....]

Guys there are a few questions i wanted to make sure that they are correct
1-heat the solution--> i wrote to seperate crystals from water
2-what type of organic compound has the following linkage--->polyester
3-the complete question an alchohol group and an acid group (didnt write organic before acid:/)
4-advantages -->biodegradable so it wont cause pollution
5-water behaves as a base-->cuz its a proton acceptor
6- for the equation between sodium flouride and calcium chloride why was double the volume of NaF added?-->i wrote cuz 1 mole of CaCl2 reacts with 2 moles of NaF
7-condensation or addition? condensation cuz water was removed from the monomer
8-the stronger acid was HCl cuz it was 97% ionized
9-ph of HCl will be lower than the other acid (Or do i have to write values)?
10-for the raw materials i wrote -->fractional distillation of liquified air and cracking of an alkane (didnt notice that the process wasnt required)
11-the moles 0.07 same as silicon?and could somebody plz explain which one is limiting and why?
12-for the T formula i got the formula wrong but i wrote the volume of phosphate solution is double the volume of metal T nitrate solution for the explanation
13-for the exothermic reaction i got the values of reactants and products and checked which has greater value
I know the q's are too many but im kinda freaked out cuz i did very badly in the exam

1 - to dry it - remove water from the precipitate
2 - well..i wrote esters, cuz they mainly asked, which type of compound got the OCO linkage, so, i think answer can be esters/fats/polyesters
3 - i think the q asked, what functional groups did the monomer have, so that, it forms an OCO linkage (ester linkage)..so i wrote..it had the -OH and the -COOH group..because, H from -OH is taken, and OH from -COOH is taken, to form water, leaving behind OCO..
4 - for this, i wrote..since its biodegredable, it wont fill up landsites, and so, more space available as landfill sites, and second, i wrote, it won't cause visual pollution (unpleasant to look at) the way normal plastics are.
5 - yup, proton acceptor
6 - my question was why was thrice the volume of something fluoride, needed to react with iron (III) something....?!?!
7 - condensation, water, yup
8 - yea, HCl strong acid, the other one weak
9 - values werent necessary, as long as you clearly wrote that, the stronger acid had a lower pH than the other one
10 - i wrote..liquid air for nitrogen, and for hydrogen, methane and steam
11 - i had 0.08 for silicon, so thts wht i wrote in the last q..and about limiting, now i dont know what mass of fluorine was given to you (some of my friends were saying that this question didnt have fluorine, but it had CHLORINE, anyone had such a question?!)
12 - i wrote my answer before.
13 - what i did was (energy used to break bonds - energy released when forming bonds), got something like -530, which means exothermic

[Kim243]

Guys there are a few questions i wanted to make sure that they are correct
1-heat the solution--> i wrote to seperate crystals from water
2-what type of organic compound has the following linkage--->polyester
3-the complete question an alchohol group and an acid group (didnt write organic before acid:/)
4-advantages -->biodegradable so it wont cause pollution
5-water behaves as a base-->cuz its a proton acceptor
6- for the equation between sodium flouride and calcium chloride why was double the volume of NaF added?-->i wrote cuz 1 mole of CaCl2 reacts with 2 moles of NaF
7-condensation or addition? condensation cuz water was removed from the monomer
8-the stronger acid was HCl cuz it was 97% ionized
9-ph of HCl will be lower than the other acid (Or do i have to write values)?
10-for the raw materials i wrote -->fractional distillation of liquified air and cracking of an alkane (didnt notice that the process wasnt required)
11-the moles 0.07 same as silicon?and could somebody plz explain which one is limiting and why?
12-for the T formula i got the formula wrong but i wrote the volume of phosphate solution is double the volume of metal T nitrate solution for the explanation
13-for the exothermic reaction i got the values of reactants and products and checked which has greater value
I know the q's are too many but im kinda freaked out cuz i did very badly in the exam

1 - to dry it - remove water from the precipitate
2 - well..i wrote esters, cuz they mainly asked, which type of compound got the OCO linkage, so, i think answer can be esters/fats/polyesters
3 - i think the q asked, what functional groups did the monomer have, so that, it forms an OCO linkage (ester linkage)..so i wrote..it had the -OH and the -COOH group..because, H from -OH is taken, and OH from -COOH is taken, to form water, leaving behind OCO..
4 - for this, i wrote..since its biodegredable, it wont fill up landsites, and so, more space available as landfill sites, and second, i wrote, it won't cause visual pollution (unpleasant to look at) the way normal plastics are.
5 - yup, proton acceptor
6 - my question was why was thrice the volume of something fluoride, needed to react with iron (III) something....?!?!
7 - condensation, water, yup
8 - yea, HCl strong acid, the other one weak
9 - values werent necessary, as long as you clearly wrote that, the stronger acid had a lower pH than the other one
10 - i wrote..liquid air for nitrogen, and for hydrogen, methane and steam
11 - i had 0.08 for silicon, so thts wht i wrote in the last q..and about limiting, now i dont know what mass of fluorine was given to you (some of my friends were saying that this question didnt have fluorine, but it had CHLORINE, anyone had such a question?!)
12 - i wrote my answer before.
13 - what i did was (energy used to break bonds - energy released when forming bonds), got something like -530, which means exothermic

for number 11 we had bromine lol...so the limting reagent will have more number of moles?

[IGCSE nightmare]

I can clearly remember that for the volume of sodium phosphate and the tnitrate it was '2cm3 and 18 cm3'...
And that what mixed me up!  May be some variant papers?!

[....]

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..