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Author Topic: Chemistry Help HERE ONLY !!  (Read 106192 times)

Offline thukon

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Re: Chemistry Help HERE ONLY !!
« Reply #570 on: May 31, 2009, 06:59:16 am »
ba da BUMP!!
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nid404

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Re: Chemistry Help HERE ONLY !!
« Reply #571 on: May 31, 2009, 07:05:38 am »
Quote from: ramezamgad on May 31, 2009, 12:27:38 am
emi
0.01 moles of CO2 were produced from the total reaction
the tablet has the same no. of moles of CaCO3 and MgCO3
so the no. of moles of CaCO3 and MgCO3 is 0.01 moles also
the no. of moles of CaCO3 only is 0.01/2 = 0.005

moles of HCl=0.01x4
no.=V x C
0.04=V x 1
V=0.04 dm3=40cm3

i think uve mistaken
CaCO3+ 2HCl--->CaCl2+CO2+H2O
same with MgCO3
so ratio of metal carbonate to Carbon dioxide is the same(1:1) for each of the carbonates, so each one is 0.01mol
so if no of moles of CO2is 0.01 then no. of moles of CaCO3 is also 0.01
and
conc=mol/dm3
no of moles of HCl is 0.02 because mole ratio is 1:2(CaCO3+2HCl)
so if metal carbonate is 0.01, HCl is 0.01x2=0.02
1mol/dm3= 0.02/vol
volume=0.02/1
=0.02dm3or 20cm3
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Offline cactus_360

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Re: Chemistry Help HERE ONLY !!
« Reply #572 on: May 31, 2009, 07:08:42 am »
nope nid ur wrong
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nid404

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Re: Chemistry Help HERE ONLY !!
« Reply #573 on: May 31, 2009, 07:11:36 am »
Quote from: cactus_360 on May 31, 2009, 07:08:42 am
nope nid ur wrong

but how come. by the mole ratio this is how it is supposed to be. is there any additional info in this question.....which paper?
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Offline SGVaibhav

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Re: Chemistry Help HERE ONLY !!
« Reply #574 on: May 31, 2009, 07:17:03 am »
i am getting confused about the term structural formula

because in one question we have to draw the structural formula


so my answers was

NH2-NH2



In markscheme


H   H
|    |
N-  N
|    |
H   H
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nid404

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Re: Chemistry Help HERE ONLY !!
« Reply #575 on: May 31, 2009, 07:18:55 am »
Quote from: nid404 on May 31, 2009, 07:05:38 am
Quote from: ramezamgad on May 31, 2009, 12:27:38 am
emi
0.01 moles of CO2 were produced from the total reaction
the tablet has the same no. of moles of CaCO3 and MgCO3
so the no. of moles of CaCO3 and MgCO3 is 0.01 moles also
the no. of moles of CaCO3 only is 0.01/2 = 0.005

moles of HCl=0.01x4
no.=V x C
0.04=V x 1
V=0.04 dm3=40cm3

i think uve mistaken
CaCO3+ 2HCl--->CaCl2+CO2+H2O
same with MgCO3
so ratio of metal carbonate to Carbon dioxide is the same(1:1) for each of the carbonates, so each one is 0.01mol
so if no of moles of CO2is 0.01 then no. of moles of CaCO3 is also 0.01
and
conc=mol/dm3
no of moles of HCl is 0.02 because mole ratio is 1:2(CaCO3+2HCl)
so if metal carbonate is 0.01, HCl is 0.01x2=0.02
1mol/dm3= 0.02/vol
volume=0.02/1
=0.02dm3or 20cm3

ok.....so the no. of moles of CaCO3and MgCO3is the same...as in they are together in the tablet...my bad
yeah so the no of moles of the single metal carbonate=0.005mol
but rest of it is correct.....i'm sure ;)
« Last Edit: May 31, 2009, 07:21:57 am by nid404 »
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nid404

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Re: Chemistry Help HERE ONLY !!
« Reply #576 on: May 31, 2009, 07:20:49 am »
Quote from: sgvaibhav on May 31, 2009, 07:17:03 am
i am getting confused about the term structural formula

because in one question we have to draw the structural formula


so my answers was

NH2-NH2



In markscheme


H   H
|    |
N-  N
|    |
H   H

when they say drawu draw the structure. when they simply say give the structural formula u can either draw or write it(like the way u have). ive been doing it that way and i think it's right.
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Offline cactus_360

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Re: Chemistry Help HERE ONLY !!
« Reply #577 on: May 31, 2009, 07:42:10 am »
nov 2008 chem p3 was DA EASIEST EVER.........I HOPE IT COMES LIKE THAT THIS TIME
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Offline astarmathsandchemistry

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Re: Chemistry Help HERE ONLY !!
« Reply #578 on: May 31, 2009, 07:46:55 am »
Quote from: cactus_360 on May 31, 2009, 07:42:10 am
nov 2008 chem p3 was DA EASIEST EVER.........I HOPE IT COMES LIKE THAT THIS TIME
that was the one  i did :P
A******* :P
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zara

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Re: Chemistry Help HERE ONLY !!
« Reply #579 on: May 31, 2009, 07:49:48 am »
but then i heard that ppr for our batch will b difficult.... :-\
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Offline idol2009

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Re: Chemistry Help HERE ONLY !!
« Reply #580 on: May 31, 2009, 07:52:37 am »
 Question on a past paper: on the October/November 2006 paper 3, question 8 ciii)...
It shows the formulas of 2 fats, and asks you how you would distinguish between the 2 fats, and asks you for the test and results.
Well, i thought it was pretty obvious it was the bromine test, but i wasn't quite sure how to tell which compound was saturated and which one was unsaturated..?
I'd appreciate it if anyone could help =)
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=)

Offline THEIGBOY

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Re: Chemistry Help HERE ONLY !!
« Reply #581 on: May 31, 2009, 08:00:43 am »
Quote from: idol2009 on May 31, 2009, 07:52:37 am
Question on a past paper: on the October/November 2006 paper 3, question 8 ciii)...
It shows the formulas of 2 fats, and asks you how you would distinguish between the 2 fats, and asks you for the test and results.
Well, i thought it was pretty obvious it was the bromine test, but i wasn't quite sure how to tell which compound was saturated and which one was unsaturated..?
I'd appreciate it if anyone could help =)
@idol2009
Bromine water will react with unsaturated compounds (in this case the unsaturated fats), but it won't react with saturated ones.
So basically when you add bromine water to a fat and it goes colourless, then it is unsaturated.
and if it stays red/brown then the fat is saturated
Hope it helps....
THEIGBOY
« Last Edit: May 31, 2009, 08:06:21 am by THEIGBOY »
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Offline idol2009

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Re: Chemistry Help HERE ONLY !!
« Reply #582 on: May 31, 2009, 08:54:00 am »
Yes, I know the bromine test for unsaturation is that but the question gives the structural formulas of two fats and basically asks which one is saturated
The fats are like this :

fat 1:
CH2 - CO2 - C17H33
|
CH - CO2 - C17H33
|
CH2 - CO2 - C17H33

fat 2:
CH2 - CO2 - C17H35
|
CH - CO2 - C17H33
|
CH2 - CO2 - C17H35

How are you supposed to know which one is saturated?
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Offline THEIGBOY

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Re: Chemistry Help HERE ONLY !!
« Reply #583 on: May 31, 2009, 09:06:16 am »
@idol2009
the first one is unsaturated.

Look....
on the first fat, it says at the end of the chain of first and last ester.
C17H33
while on  the second fat...
C17H35

Over there the formula for saturated compounds is
CnH2n+1
while for unsaturated
CnH2n-1


So for 17 carbons (at the end only)----> H (hydrogen) = 2(17) + 1 = 35 ----> for saturated
                                                        H (hydrogen) = 2(17) - 1 = 33 ----> for unsaturated

Hope it helps
« Last Edit: May 31, 2009, 09:08:18 am by THEIGBOY »
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Offline Shogun

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Re: Chemistry Help HERE ONLY !!
« Reply #584 on: May 31, 2009, 09:09:21 am »
wat my teacher said,more saturated means more hydrogen
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