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Author Topic: CHEM AND BIO HELP AND TIPS HERE  (Read 353919 times)

Offline The Golden Girl =D

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2010 on: May 24, 2010, 06:45:10 pm »
Quote from: ~VIN1094~ on May 24, 2010, 06:40:58 pm
yes but it has to dissociate with water to give H+ to show its acidity ..

VIN (i kno u'll kill me but anyways) .... when does Hydrogen have an ion ....u say dissociate with water ,so is there any other way it get's an ion charge thingy
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Offline WARRIOR

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2011 on: May 24, 2010, 06:50:16 pm »
hmmm

isnt this supposed to be MG0 + H2?

MARK SCHEME SAYS A :/
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Offline Ghost Of Highbury

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2012 on: May 24, 2010, 06:52:10 pm »
Quote from: Kimo Jesus on May 24, 2010, 06:50:16 pm
hmmm

isnt this supposed to be MG0 + H2?

MARK SCHEME SAYS A :/
are you sure? check the markscheme again..if its steam it should be magnesium oxide + hydrogen
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Offline haris94

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2013 on: May 24, 2010, 06:54:08 pm »
yea....it should be MgO + H2
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Offline Vin

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2014 on: May 24, 2010, 06:54:54 pm »
Quote from: the golden girl on May 24, 2010, 06:45:10 pm
VIN (i kno u'll kill me but anyways) .... when does Hydrogen have an ion ....u say dissociate with water ,so is there any other way it get's an ion charge thingy

its ok its good to ask ques .. listen hydrogen has an ion when it is bound with a cation meaning when it is in an acid form .. eg HCl .. when HCl disassociates in water is gives out H+ ion .. this ion is very unstable so it combines with H2O .. to give H3O+ .. u see that PLUS over H3O ?? tht is very IMPORTANT it is called hydronium ion .. the concentration of THIS "ION" .. i repeat ION !! very imp because there is nothing lik H3O compound !! so the concentration of this ion determines the 'strength' of an acid .. also an acid solution is acidic due to this ion ..

i'll tell u something  .. DRY HCl gas doesnt turn blue litmus red .. y ?? because u need to WET the litmus to gain the change the colour diff .. when u wet it H+ ions are produced with are acidic ;)
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Offline the_grim_reaper

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2015 on: May 24, 2010, 06:57:09 pm »
Quote from: Kimo Jesus on May 24, 2010, 06:50:16 pm
hmmm

isnt this supposed to be MG0 + H2?

MARK SCHEME SAYS A :/


Which year is it??? I mean if it isn't an official document from CIE, (like the ones for 00 or 01 here) it has mistakes....
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Offline the_grim_reaper

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2016 on: May 24, 2010, 06:59:01 pm »
Quote
Plus one final thing people, in June 2000, shouldn't question 30 be C??? (Paper 1 Chemistry)

Can someone please help me here too?? The mark scheme says that if you add S02 to water, the pH goes above 7 (alkaline)
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Offline ambitious94

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2017 on: May 24, 2010, 07:01:54 pm »
A student carries out an experiment to prepare pure magnesium sulfate crystals.
The diagram shows the first stage of the preparation.
In diagram :
-dilute sulfuric acid
-stirrer
-magnesium carbonate
He adds magnesium carbonate until no more reacts.
Which process should he use for the next stage?
A crystallisation
B evaporation
C filtration
D neutralisation

I thght it's A. But turns out it's C. Is Magnesium sulphate insoluble in water? :S
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Offline WARRIOR

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2018 on: May 24, 2010, 07:03:32 pm »
oct / nov 1997

anwa a tricky question  ( for me anyway )  i got it wrong ..asnwr is A






asner should be filtration..you filter first then evaporate
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Offline Ghost Of Highbury

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2019 on: May 24, 2010, 07:07:39 pm »
Quote from: Kimo Jesus on May 24, 2010, 07:03:32 pm
oct / nov 1997

anwa a tricky question  ( for me anyway )  i got it wrong ..asnwr is A






asner should be filtration..you filter first then evaporate

A - CH4 + 2O2 = CO2 + 2H2O 

  H2O = colorless liquid......

  CO2 = colorless gas - limewater milky
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Offline Ghost Of Highbury

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2020 on: May 24, 2010, 07:08:14 pm »
Quote from: deadman786 on May 24, 2010, 06:59:01 pm
Can someone please help me here too?? The mark scheme says that if you add S02 to water, the pH goes above 7 (alkaline)

i cant open that paper??!!
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Offline the_grim_reaper

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2021 on: May 24, 2010, 07:09:09 pm »
Quote from: ambitious94 on May 24, 2010, 07:01:54 pm
A student carries out an experiment to prepare pure magnesium sulfate crystals.
The diagram shows the first stage of the preparation.
In diagram :
-dilute sulfuric acid
-stirrer
-magnesium carbonate
He adds magnesium carbonate until no more reacts.
Which process should he use for the next stage?
A crystallisation
B evaporation
C filtration
D neutralisation

I thght it's A. But turns out it's C. Is Magnesium sulphate insoluble in water? :S



No. All sulphates except those lead, barium and calcium are soluble.

You filter to remove any excess magnesium carbonate (which is insoluble). Adding it till no more reacts means that you must've added some excess magnesium carbonate (which is insoluble). First it must be removed by filtration then crystallisation can be used to obtain magnesium sulphate crystals
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Offline Vin

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2022 on: May 24, 2010, 07:09:19 pm »
Quote from: Kimo Jesus on May 24, 2010, 07:03:32 pm
oct / nov 1997

anwa a tricky question  ( for me anyway )  i got it wrong ..asnwr is A






asner should be filtration..you filter first then evaporate

easy .. look at the options .. try CH4 first .. does it burn in air to give water and CO2 ?? yes .. voila !! water is 100 *C boiling pt and CO2 lime watre colourless to cloudy..

answer is A
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Offline ambitious94

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2023 on: May 24, 2010, 07:16:55 pm »
Quote from: deadman786 on May 24, 2010, 07:09:09 pm


No. All sulphates except those lead, barium and calcium are soluble.

You filter to remove any excess magnesium carbonate (which is insoluble). Adding it till no more reacts means that you must've added some excess magnesium carbonate (which is insoluble). First it must be removed by filtration then crystallisation can be used to obtain magnesium sulphate crystals
Oh God that was so obvious!!! LOL...THANKSSSSSSSSSSS! :)
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Offline Horse Lover

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #2024 on: May 24, 2010, 07:17:41 pm »
CAN SOMEONE PLEASE TELL ME WHAT IS PRECIPITATION???

Also... when the give u an equation.. how do u know if it is a redox or oxidation???

Please Notify me :)
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