Qualification > Sciences
IG Chemistry Paper 3 discussion
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 ;D
....:
--- Quote from: Kim243 on June 03, 2009, 10:23:51 am ---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
--- End quote ---
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:
--- Quote from: .... on June 03, 2009, 12:36:13 pm ---
--- Quote from: Kim243 on June 03, 2009, 10:23:51 am ---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
--- End quote ---
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
--- End quote ---
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? :P
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 Ar
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..
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