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Biology; Chemistry; Physics: Post your doubts here!

Vogue

Vogue

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is percentile calculated among students of ONE center or is it city or country wide??? nd is it even possible that percentile is raised rather than lowered due to sum students who do out standing ppr?
 
Rimsa

Rimsa

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Vogue said:
is percentile calculated among students of ONE center or is it city or country wide??? nd is it even possible that percentile is raised rather than lowered due to sum students who do out standing ppr?
Click to expand...
dutn know about anything else but my teacher used to say that having those 'ginnies' in your session wont do US any good. when its percentile, it means you need to be among the best
 
Ahmedfj

Ahmedfj

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Hey guys i didnt shade the candidate number grid in bio paper becoz i didnt know .. will they check my paper or not ?? em really worried
 
malay

malay

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snowbrood said:
http://www.xtremepapers.com/papers/CIE/Cambridge International O Level/Chemistry (5070)/5070_w05_qp_2.pdf here it is Q5 a(ii),b
Click to expand...
a: moles of HCl
mol=molarity (mol/dm3).volume(dm3)
=1.5*25/1000
=0.0375mol
than frm eq as 2 mol of HCl produce 1 mol of CO2
0.0375/2=0.01875mol of Co2 r produced
now use formula
Volume=mol*24dm3
=0.01875*24
=0.45dm3 of CO2 is produced-Ans
b: as seen frm da graph
volume of exp 2 is half dat of 1.therefore
vol of exp =25/2=12.5cm3
n conc=1.5/2=0.75mol.dm3
hope u understand........
 
snowbrood

snowbrood

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malay said:
a: moles of HCl
mol=molarity (mol/dm3).volume(dm3)
=1.5*25/1000
=0.0375mol
than frm eq as 2 mol of HCl produce 1 mol of CO2
0.0375/2=0.01875mol of Co2 r produced
now use formula
Volume=mol*24dm3
=0.01875*24
=0.45dm3 of CO2 is produced-Ans
b: as seen frm da graph
volume of exp 2 is half dat of 1.therefore
vol of exp =25/2=12.5cm3
n conc=1.5/2=0.75mol.dm3
hope u understand........
Click to expand...
these answers are what i got but these dont match with the mark scheme
 
snowbrood

snowbrood

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scouserlfc said:
the thing is that in 2 the gas produced is half the previous volume in experiment 1 so it has half the concentration of the solution used in 1 !
Play with the molarity equation and u will understand it and btw make volume a constant when u play !
Click to expand...
i dont get it graphs says that exp1 produces twice the volume of exp2 but the markscheme says that they are both the same?
 
scouserlfc

scouserlfc

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snowbrood said:
i dont get it graphs says that exp1 produces twice the volume of exp2 but the markscheme says that they are both the same?
Click to expand...

Look at the er it will guide u much better here !
U should get the idea that concentration is less due to less gas produced and the slope of line in 2 is less than in 1
 
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