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Author Topic: Chemistry Help HERE ONLY !!  (Read 107739 times)

Offline Shogun

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Re: Chemistry Help HERE ONLY !!
« Reply #300 on: May 29, 2009, 03:09:56 pm »
lol y dint i think bout that..Thanks mate :D
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Offline Coco

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Re: Chemistry Help HERE ONLY !!
« Reply #301 on: May 29, 2009, 03:13:47 pm »
eyy yall
err i was wonderin if sum1 cud upload tha marking schemes for the year 2000 may/ june n Oct/ nov
n also 2001!!
ayt
also was wonderin how many past papers shall i solve in order to get an A*? 8)
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Offline unknown 101

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Re: Chemistry Help HERE ONLY !!
« Reply #302 on: May 29, 2009, 03:18:43 pm »
Quote from: Coco on May 29, 2009, 03:13:47 pm
eyy yall
err i was wonderin if sum1 cud upload tha marking schemes for the year 2000 may/ june n Oct/ nov
n also 2001!!
ayt
also was wonderin how many past papers shall i solve in order to get an A*? 8)

hahaah, how about doing 10 YEARS of pastpapers just to guarentee ur A*
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Offline Shogun

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Re: Chemistry Help HERE ONLY !!
« Reply #303 on: May 29, 2009, 03:20:00 pm »
lol atleast onwards 2005 or like lil wayne said....(lol but lil waynes idea, woulf give u 98% sure tht ull get A*)lol
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Offline emi

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Re: Chemistry Help HERE ONLY !!
« Reply #304 on: May 29, 2009, 03:21:57 pm »
thanks guys i get the first part all now .. but about part ii  the max moles ,  is it like always if there is one mole it will me 0.08 ?
and why we didnt use the 10.4 in anything ??

can some one just complete that part till the percentage yield thanks <3
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Offline Coco

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Re: Chemistry Help HERE ONLY !!
« Reply #305 on: May 29, 2009, 03:23:11 pm »
im aiming for a 100% :) [which i wont get cuz i screwed up paper 6]
n yes 10 years is ideal
Thanx yo!
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Offline lana

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Re: Chemistry Help HERE ONLY !!
« Reply #306 on: May 29, 2009, 03:28:38 pm »
somebody please explain this to me ...when a reaction cool or lose heat it's endothermic right ? because energy is taken in ? please correct me if I'm wrong because in pp3 in June 08 mark scheme  it's the opposite !!! so I'm totally confused  :-\
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Offline unknown 101

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Re: Chemistry Help HERE ONLY !!
« Reply #307 on: May 29, 2009, 03:30:40 pm »
Quote from: emi on May 29, 2009, 03:21:57 pm
thanks guys i get the first part all now .. but about part ii  the max moles ,  is it like always if there is one mole it will me 0.08 ?
and why we didnt use the 10.4 in anything ??

can some one just complete that part till the percentage yield thanks <3

its because you do not know the mass of NiSO4 that reacted, maybe half of it reacted , all u know i that the number of moles of NiSO4 is 0.08 mol
and since it is 1:1 ratio so, if all the NiSO4 reacted that means that maximun number of crystals would be fromed which has a mol of 0.08 (1:1 ratio)
and to find the maximum mass use the formula: mass = moles x mr ----> 0.08  x  281 = 22.48
so that is the maxmun mass that could be produced
the percentage yeild is given by the formula : mass given/theoritical amount  x 100
so in this case 10.4/22.48  x 100  =   46.3%
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Offline unknown 101

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Re: Chemistry Help HERE ONLY !!
« Reply #308 on: May 29, 2009, 03:33:53 pm »
Quote from: lana on May 29, 2009, 03:28:38 pm
somebody please explain this to me ...when a reaction cool or lose heat it's endothermic right ? because energy is taken in ? please correct me if I'm wrong because in pp3 in June 08 mark scheme  it's the opposite !!! so I'm totally confused  :-\

hahahah ur right, but in jun08 u misunderstood it probabley, cuz over the arrow its says cool, that means that when u cool it it gives u a greater yeild of COCl2, because the forward reaction is exo so decreasing temp would shift equliberium to the right , to increase temp thus producing more yeild of COCl2
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Offline emi

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Re: Chemistry Help HERE ONLY !!
« Reply #309 on: May 29, 2009, 03:37:00 pm »
thanks alot
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Offline unknown 101

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Re: Chemistry Help HERE ONLY !!
« Reply #310 on: May 29, 2009, 03:38:31 pm »
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Offline lana

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Re: Chemistry Help HERE ONLY !!
« Reply #311 on: May 29, 2009, 03:39:36 pm »
ooh ok !!! :P thanks alot and seriously lilwayne your the best !!! ;D
+rep for you
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Offline unknown 101

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Re: Chemistry Help HERE ONLY !!
« Reply #312 on: May 29, 2009, 03:41:00 pm »
Quote from: lana on May 29, 2009, 03:39:36 pm
ooh ok !!! :P thanks allot and seriously lilwayne your the best !!! ;D
+rep for you

Thanks  :D
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Offline emi

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Re: Chemistry Help HERE ONLY !!
« Reply #313 on: May 29, 2009, 03:44:50 pm »
Quote
somebody please explain this to me ...when a reaction cool or lose heat it's endothermic right ? because energy is taken in ? please correct me if I'm wrong because in pp3 in June 08 mark scheme  it's the opposite !!! so I'm totally confused  Undecidedaa

i think you are wrong .. because when a reaction lose heat means its exothermic  and when it takes heat in then its endothermic when it loses energy then how is the energy takin in ?  that happens in endothermic reactions where it takes energy in , exothermic gives energy out .

and MS is correct
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Offline unknown 101

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Re: Chemistry Help HERE ONLY !!
« Reply #314 on: May 29, 2009, 03:47:53 pm »
Quote from: emi on May 29, 2009, 03:44:50 pm
Quote
somebody please explain this to me ...when a reaction cool or lose heat it's endothermic right ? because energy is taken in ? please correct me if I'm wrong because in pp3 in June 08 mark scheme  it's the opposite !!! so I'm totally confused  Undecidedaa

i think you are wrong .. because when a reaction lose heat means its exothermic  and when it takes heat in then its endothermic when it loses energy then how is the energy takin in ?  that happens in endothermic reactions where it takes energy in , exothermic gives energy out .

and MS is correct


emi she got confused cuz in the jun08 there is a reversible reaction and on the top  arrow it says cool, so she thought it was endothermic but in the markscheme the froward reaction is exo, im sure she knows the differanc between exo and endo
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