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Author Topic: CHEM AND BIO HELP AND TIPS HERE  (Read 354317 times)

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #825 on: May 16, 2010, 10:50:27 am »
Quote from: Fastal on May 16, 2010, 10:20:03 am
whats a colourimeter thing? is it like a data loggeror colour comparer
is this "colourimeter" in som mark scheme or somthin
if yes plz tel which yr n blahla
if no ,den tel me where did u fynd this wrd
 Thanks ;D :D ;) :P
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Offline gold_wings

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #826 on: May 16, 2010, 10:56:11 am »
Calorimeter is used for measuring the heat of chemical reactions or heat capacities
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Offline WARRIOR

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #827 on: May 16, 2010, 10:56:45 am »
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Offline K_M

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #828 on: May 16, 2010, 10:57:58 am »
Quote from: Mathewness on May 16, 2010, 09:11:37 am
Bond breaking is endothermic because the molecules are using energy from the surroundings to 'break' their bonds.
Bond forming  is exothermic because of a reason, which im not quite sure is relevant to IGs... two molecules start off at a higher energy. When they bond together, they become more stable and release energy.

oh yea sorry by mistake i wrote exothermic for bond breaking and bond formation!
Anyway what you just said makes sense but then how is 2N + O2 ---> 2NO endothermic?! Since nitrogen is combining with oxygen shouldnt it be exothermic?!
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Offline omair

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #829 on: May 16, 2010, 10:58:26 am »
Quote from: princess12 on May 16, 2010, 10:09:40 am
on 2007 p6 Q 4d
for bio or chem
 ??? ??? ??? ??? ??? ??? ??? ??? ??? ??? ???
reply me fast urgent reply
 ??? ??? ??? ???
oct nnov chemistry i a msorry
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Offline Kim

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #830 on: May 16, 2010, 10:58:50 am »
a colorimeter is a device used to measure the intensity of colour of a solution
u just need to know wen to use it for igcse
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Offline Vin

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #831 on: May 16, 2010, 11:00:00 am »
Quote from: gold_wings on May 16, 2010, 10:56:11 am
Calorimeter is used for measuring the heat of chemical reactions or heat capacities

They are talking about "Colorimeter" ur talking abt    "Calorimeter" .. get it ??
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Offline Vin

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #832 on: May 16, 2010, 11:00:19 am »
Quote from: ~VIN1094~ on May 16, 2010, 10:45:14 am
i dont think colourimeter is a data logger .. colourimeter si a device measures the absorbance of wavelengths of light by a specific given solution. we hav it in our lab .. jus a small thing (looks lik a weighing scale without the plate) has a hole where a test tube can fit in .. had almost forgotten abt it !!

data logger records data over time .. thts wat i remember .. =\


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Offline Vin

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #833 on: May 16, 2010, 11:07:18 am »
Quote from: Kimo Jesus on May 16, 2010, 10:56:45 am
http://www.freeexampapers.us/IGCSE/Chemistry/CIE/2005%20Jun/0620_s05_qp_6.pdf

q5 3? why green ppt.

Test for Copper(II)

That indicates tht the cation is Cu2+

green solution formed
dark blue solution formed

already given in the ques. ..
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Offline ismailb_1993

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #834 on: May 16, 2010, 11:08:08 am »
Quote from: Mathewness on May 16, 2010, 09:11:37 am
Bond breaking is endothermic because the molecules are using energy from the surroundings to 'break' their bonds.
Bond forming  is exothermic because of a reason, which im not quite sure is relevant to IGs... two molecules start off at a higher energy. When they bond together, they become more stable and release energy.

It is also because the endothermic reaction needs more energy than the exothermic reaction...its a simple explanation. Every reaction has an endothermic and exothermic reaction involved, it just depends on which one requires more energy. When they say the reaction is endothermic, then OVERALL, the exothermic reaction needs less energy than the endothermic reation, and vice versa for exothermic reactions.
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Offline K_M

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #835 on: May 16, 2010, 11:10:53 am »
Quote from: ismailb_1993 on May 16, 2010, 11:08:08 am
It is also because the endothermic reaction needs more energy than the exothermic reaction...its a simple explanation. Every reaction has an endothermic and exothermic reaction involved, it just depends on which one requires more energy. When they say the reaction is endothermic, then OVERALL, the exothermic reaction needs less energy than the endothermic reation, and vice versa for exothermic reactions.

oh i get it know! Thanks! =)
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Offline Vin

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #836 on: May 16, 2010, 11:12:02 am »
Quote from: K_M on May 16, 2010, 10:57:58 am
oh yea sorry by mistake i wrote exothermic for bond breaking and bond formation!
Anyway what you just said makes sense but then how is 2N + O2 ---> 2NO endothermic?! Since nitrogen is combining with oxygen shouldnt it be exothermic?!

synthesis of N2 and O2 requires a lot of heat .. tht is why NO is formed in the presence of lightning naturally in the atmosphere
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Offline gold_wings

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #837 on: May 16, 2010, 11:14:39 am »
Quote from: ~VIN1094~ on May 16, 2010, 11:07:18 am
Test for Copper(II)

That indicates tht the cation is Cu2+

green solution formed
dark blue solution formed

already given in the ques. ..

I get that the dark blue is copper 2+ but isnt green ppt iron (II)?
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Offline Vin

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #838 on: May 16, 2010, 11:29:22 am »

Yea i kno even i was foxed by this one .. yes for Iron(II) its green ppt.., insouble in excess so solid B was added so prolly it had Fe 2+   i forcefully had look in the ms !! these kinda are always dicey .. i'll ask my sir .. abt it .. ;)
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Offline Lariemeeva

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Re: CHEM AND BIO HELP AND TIPS HERE
« Reply #839 on: May 16, 2010, 11:39:55 am »
Got two doubts.

Firstly, I'm looking for any Notes/Diagrams/Worksheets on The Chemistry Lab apparatus, where they are all listed and named. I have already tried the Resources at freepastpapers.com and it does not come n handy as the notes are missing a lot.

Secondly, the syllabus mentions that we should describe the test for aqueous zinc cations, it's not in my Collins Chemistry book, so can anyone elaborate on this test?

Plus, I have a tiny request, if anyone has any good links to some great notes for Paper 6 Chemistry, I have already checked the notes submitted in this forum as a post, but they're kind of confusing.

Thanks in advance...
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