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Author Topic: Edexcel CHEMISTRY DOUBTS!!!!  (Read 253419 times)

Offline coatseville

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #330 on: June 06, 2010, 08:45:53 pm »
no problem the x2 is because the error could have either resulted in the value moving above or below the figure we were given so we have to take that into account and the .5 is because it is always the way we determine if we round a number or not. but the x2 and the .5 is used in all of the % error questions its just the number of dp's (ie 0.005 or 0.5) that changes...
idk if im explaining tht well its quite hard to explain but yah.. :)
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Offline Kim

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #331 on: June 06, 2010, 08:49:00 pm »
Quote from: coatseville on June 06, 2010, 08:45:53 pm
no problem the x2 is because the error could have either resulted in the value moving above or below the figure we were given so we have to take that into account and the .5 is because it is always the way we determine if we round a number or not. but the x2 and the .5 is used in all of the % error questions its just the number of dp's (ie 0.005 or 0.5) that changes...
idk if im explaining tht well its quite hard to explain but yah.. :)

ok i get .5 part
but correct me if i am wrong so we are gonna use 2 in all the questions??or does it change?
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Offline Kim

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #332 on: June 06, 2010, 08:59:35 pm »
hey u there???
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Offline ksitna

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #333 on: June 06, 2010, 09:08:22 pm »
Quote from: kim on June 06, 2010, 08:59:35 pm
hey u there???


lol im sorry but tht made me llaugh :P

and i need help with tht on too :(
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Offline Kim

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #334 on: June 06, 2010, 09:09:40 pm »
Quote from: ksitna on June 06, 2010, 09:08:22 pm
lol im sorry but tht made me llaugh :P

and i need help with tht on too :(

glad i cud make u laugh
hahahaa join the club
i only understood the 0.5 part and i just wanna if we always use 2
but apprently that persons gone poof
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Offline Uchia

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #335 on: June 06, 2010, 09:18:10 pm »
hey

i'll help a bit

in all the percentage error questions u use the 0.05 ( it could be 0.005 it depends on the question but the june 09 question said to 2 dp so take 0.05)

0.05*2 u should always multiply by 2 just like what the previous fellow said and then u divide by orginal * 100 to get percentage
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Offline Kim

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #336 on: June 06, 2010, 09:21:07 pm »
Quote from: damlaj on June 06, 2010, 09:18:10 pm
hey

i'll help a bit

in all the percentage error questions u use the 0.05 ( it could be 0.005 it depends on the question but the june 09 question said to 2 dp so take 0.05)

0.05*2 u should always multiply by 2 just like what the previous fellow said and then u divide by orginal * 100 to get percentage

ok thanks in the ms it says u multiply by 0.005
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Offline Uchia

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #337 on: June 06, 2010, 09:21:41 pm »
sometimes in the question itself they give u the percentage error so no need to use the 0.***5 cz as u should know specific/different apparatus have different accuracy
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Offline Kim

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #338 on: June 06, 2010, 09:22:54 pm »
Quote from: damlaj on June 06, 2010, 09:21:41 pm
sometimes in the question itself they give u the percentage error so no need to use the 0.***5 cz as u should know specific/different apparatus have different accuracy

ok thank you dude u really helped
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Offline Uchia

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #339 on: June 06, 2010, 09:30:26 pm »
:( i don't know about that cz in the unit 3 similar questions they did as i told u seems weird
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Offline Sweet_03

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #340 on: June 06, 2010, 09:33:05 pm »
hey guys , can someone pls explain the rate of reactions of the halogenalkanes (primary, secondary, tertiary) .. which one is the fastest/slowest .. and why ? :")
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Offline Uchia

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #341 on: June 06, 2010, 09:37:25 pm »
fastest tertiary, then secondary then primary as for y? ill figure out and then i'll tell u cz am not sure of the answer i don't want to confuse u
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Offline GodOfWar

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #342 on: June 06, 2010, 09:43:37 pm »
Quote from: Sweet_03 on June 06, 2010, 09:33:05 pm
hey guys , can someone pls explain the rate of reactions of the halogenalkanes (primary, secondary, tertiary) .. which one is the fastest/slowest .. and why ? :")


Are u talkig abt elimination or substitution reactions?
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Offline Uchia

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #343 on: June 06, 2010, 09:48:37 pm »
subsitution

well as i could think of

tertiary reacts by SN1 involves 2 steps
Secondary could go both
Primary reacts by SN2 invloves 1 step

as u know SN1 is faster so tertiary is faster if i found more convincing explanation i'll tell u as soon as possible
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Offline Darth Austrakast

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #344 on: June 07, 2010, 02:57:48 am »
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