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Author Topic: Edexcel CHEMISTRY DOUBTS!!!!  (Read 246801 times)

Offline ~ Miss Relina ~

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #870 on: April 12, 2011, 02:25:53 pm »
Quote from: Blizz_rb93 on April 12, 2011, 02:23:02 pm
Explain why the different fractions of crude oil are collected at different temperatures?

due to different boiling points for each fraction so differnt volatility so fractions are collected faster than other due to weaker  :)forces
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Offline Shazizzzle

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #871 on: April 12, 2011, 08:42:05 pm »
Quote from: Blizz_rb93 on April 12, 2011, 02:23:02 pm
Explain why the different fractions of crude oil are collected at different temperatures?

The boiling points of hydrocarbons depend on the intermolecular forces between the hydrocarbon molecules. They have simple van der waals forces between them.
As the hydrocarbons get larger, their Mr, size, and the total number of electrons increase, and therefore the van der waals forces between them get stronger, and so more energy is needed to 9vercome those stronger forces and hence the increasing boiling point. :)

Simply, more electrons, stronger intermolecular forces,  higher boiling and melting points.
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Offline moalna

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #872 on: April 13, 2011, 09:32:15 am »
Quote from: Summer :] on May 09, 2010, 04:46:22 pm
i have a question
why do we have to add the sulphuric acid slowly when preparing the bromoalkane from alcohol?

I think thats because the reaction is exothermic and it is done to prevent over heating. If you add slowly, most of the heat generated will be lost to the surrounding and the mixture container will cool down a little bit before you add the next drop of sulphuric acid. If you add it quickly, the effect of the heat generated will be too much.
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Offline ~ Miss Relina ~

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #873 on: April 13, 2011, 01:11:45 pm »
how to decide whether the last answer to any question would be whether 2/3/4 s.f.?
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Offline The Golden Girl =D

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #874 on: April 13, 2011, 01:13:44 pm »
Quote from: Relina on April 13, 2011, 01:11:45 pm
how to decide whether the last answer to any question would be whether 2/3/4 s.f.?


My teacher tells me write it in 3 s.f. to be on the safe side :)

Notice sometimes in the Questions they ask for 2 s.f. or 3s.f. ,in that case you write it down in the form they asked ;)
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Offline Master_Key

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #875 on: April 13, 2011, 02:37:17 pm »
Quote from: Relina on April 13, 2011, 01:11:45 pm
how to decide whether the last answer to any question would be whether 2/3/4 s.f.?


Read the first page of your exam paper. It specifies to write to any s.f.

In CIE GCE AS/A Level - Maths - 9709.

Give non-exact numerical answers correct to 3 significant figures, or 1 decimal place in the case of angles in
degrees, unless a different level of accuracy is specified in the question.
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Offline red_911

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #876 on: April 13, 2011, 05:34:27 pm »
its a silly question but i dont understand how valency of nitrate (NO3) is -1
like shouldnt it be +3+ -2*3 = -3    ???
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elemis

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #877 on: April 13, 2011, 05:45:55 pm »
Quote from: red_911 on April 13, 2011, 05:34:27 pm
its a silly question but i dont understand how valency of nitrate (NO3) is -1
like shouldnt it be +3+ -2*3 = -3    ???

Nitrogen can have variable valencies. In this case it is 5.

Hence, 5-6=-1
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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #878 on: April 13, 2011, 06:25:22 pm »
Hey guys, I need a little bit of help here, for the priority list of functional groups, so far I've seen "3 versions" and I'm really hoping I don't get to encounter more!

Can someone please confirm for me which one is the right one?

Version #1:
Carboxylic Acids > Sulphonic Acid > Acid Anhydride > Esters > Acyl halide> Amide > Aldehyde > Ketones > Nitriles > Alcohols > Amino > Ethers > Alkenes > Alkynes > Substituents

Version #2:
Carboxylic Acids > Sulphonic Acids > Acid Anhydride > Esters > Acyl Halides > Amides > Nitriles > Aldehydes > Ketones > Alcohols > Amines > Alkyne > Alkene

Version #3:
The one I'm finding online here: http://www.chem.ucalgary.ca/courses/351/orgnom/functional/func.html

-----------------------------------------------------------

Question 2: How do you name this compound?
CH3CH(SO3H)=CH2COOH
Is it 3-Sulphobutanoic acid OR 3-Sulphobutan-2-oic acid?
-----------------------------------------------------------

Question 3: If we have a compound like this: NH2-CH2-CH2-CH2-CH2-NH2 does it make a difference if we name it 1,4-Butanediamine OR Butane-1,4-diamine?
« Last Edit: April 13, 2011, 09:07:45 pm by The Secret »
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Offline Blizz_rb93

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #879 on: April 14, 2011, 05:29:21 am »
How the presence of a double bond affects the physical and chemical properties of the alkenes?
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elemis

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #880 on: April 14, 2011, 05:50:21 am »
Quote from: Blizz_rb93 on April 14, 2011, 05:29:21 am
How the presence of a double bond affects the physical and chemical properties of the alkenes?

Chemically they tend to react via an electrophilic mechanism.

Physical properties.... look it up in your textbook.
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Offline Blizz_rb93

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #881 on: April 14, 2011, 10:14:28 am »
How does the reaction of the alkenes with the halogens differ from the reaction of the alkanes with the halogens?
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elemis

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #882 on: April 14, 2011, 10:30:49 am »
Quote from: Blizz_rb93 on April 14, 2011, 10:14:28 am
How does the reaction of the alkenes with the halogens differ from the reaction of the alkanes with the halogens?

This rather elemetary stuff, open your textbook and read.

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Offline Aadeez || Zafar

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #883 on: April 14, 2011, 10:39:46 am »
Quote from: Blizz_rb93 on April 14, 2011, 10:14:28 am
How does the reaction of the alkenes with the halogens differ from the reaction of the alkanes with the halogens?
in alkanes+halogen, UV light should be present and u get mono-halogenoalkane and hydrogen halide ( or another longer alkane, if u study in DETAIL!) as byproduct, it is free-radical addition reaction
but in alkenes+halogen , u get di-halogenoalkane with no by product, it is neucliophilic addition reaction

SIMPLE
« Last Edit: April 14, 2011, 10:41:41 am by Mr. MUST »
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Offline Vampire-Love4ever

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Re: Edexcel CHEMISTRY DOUBTS!!!!
« Reply #884 on: April 14, 2011, 05:17:55 pm »
Hey,

Anyone having the answers to the EXAMZONE part of the questions in this textbook?

http://www.amazon.co.uk/Edexcel-Level-Science-Chemistry-Students/dp/1408206056/ref=pd_sim_b_7

Please!!! I hope someone does!!!


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