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Author Topic: Chemistry doubt  (Read 8070 times)

Offline acash09

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Chemistry doubt
« on: May 22, 2010, 05:37:41 pm »
Hey friends, what happens when an impurity is present in a substance, does:

  • boiling point change; increase or decrease
  • melting point change; increase or decrease

& when does ph increase or decrease?

e.g adding more water does what, not by neutralization. 

thanks, acash09
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Offline WARRIOR

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Re: Chemistry doubt
« Reply #1 on: May 22, 2010, 05:55:15 pm »
An impure subsance melts at a rangge BELOW THE MELTING POINT
                            boils at a range  ABOVE THE BOILING POINT

 ph gr8er 7 is alkaline .....ph  less than 7 is acidic  .

adding more water just makes somethin more DILUTE ..means less acidic/or alkaline
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Offline J.Darren

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Re: Chemistry doubt
« Reply #2 on: May 22, 2010, 07:11:29 pm »
Quote from: Kimo Jesus on May 22, 2010, 05:55:15 pm
An impure subsance melts at a rangge BELOW THE MELTING POINT
                            boils at a range  ABOVE THE BOILING POINT

 ph gr8er 7 is alkaline .....ph  less than 7 is acidic  .

adding more water just makes somethin more DILUTE ..means less acidic/or alkaline
Wait, I recall that back in 03 / 04 there is a reaction that involves Mg ribbon and acid, if you increase the volume of acid, the change in temp would decrease, same theory holds true for water, if it is a metal + water reaction, as we all know, salt and hydrogen is produced, yet the change in temperature would be smaller if greater volume of water is used. This is also a common question that appeared in Paper 6.

Kimo : Are you intended to compose a revision notes thingie for Physics P3 ?
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Offline WARRIOR

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Re: Chemistry doubt
« Reply #3 on: May 23, 2010, 10:54:27 am »
Quote from: J.Darren on May 22, 2010, 07:11:29 pm
Wait, I recall that back in 03 / 04 there is a reaction that involves Mg ribbon and acid, if you increase the volume of acid, the change in temp would decrease, same theory holds true for water, if it is a metal + water reaction, as we all know, salt and hydrogen is produced, yet the change in temperature would be smaller if greater volume of water is used. This is also a common question that appeared in Paper 6.

Kimo : Are you intended to compose a revision notes thingie for Physics P3 ?
if u mean chemistry paper 3  ..yep!
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Offline J.Darren

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Re: Chemistry doubt
« Reply #4 on: May 23, 2010, 11:14:22 am »
Quote from: Kimo Jesus on May 23, 2010, 10:54:27 am
if u mean chemistry paper 3  ..yep!
LOL my bad :D
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Offline Black

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Re: Chemistry doubt
« Reply #5 on: May 23, 2010, 11:16:58 am »
the multiple choice is on tuesday :( the paper 3 is in like 2 weeks 7th of june :D
Anyways my questions is for paper 1 (multi) do we need to knw the core material only or all of it(including extended)???
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holtadit

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Re: Chemistry doubt
« Reply #6 on: May 23, 2010, 02:50:13 pm »
Quote from: Black on May 23, 2010, 11:16:58 am
the multiple choice is on tuesday :( the paper 3 is in like 2 weeks 7th of june :D
Anyways my questions is for paper 1 (multi) do we need to knw the core material only or all of it(including extended)???

You have to know both.
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Offline Ivo

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Re: Chemistry doubt
« Reply #7 on: May 23, 2010, 02:51:33 pm »
Quote from: Ari Ben Canaan on May 23, 2010, 02:50:13 pm
You have to know both.

Oh, I thought for Papers 1 + 6 are aimed for Core curriculum.  That's why stuff like Condensation Polymerisation never comes up!
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nid404

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Re: Chemistry doubt
« Reply #8 on: May 23, 2010, 02:56:33 pm »
Yes, apparently it is based on the core syllabus. :-\ 
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Offline J.Darren

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Re: Chemistry doubt
« Reply #9 on: May 23, 2010, 06:47:35 pm »
Quote from: nid404 on May 23, 2010, 02:56:33 pm
Yes, apparently it is based on the core syllabus. :-\ 
Isn't that a good thing ??? :o
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Offline cashem'up

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Re: Chemistry doubt
« Reply #10 on: May 24, 2010, 10:25:24 am »
Quote from: J.Darren on May 23, 2010, 06:47:35 pm
Isn't that a good thing ??? :o
well yea the mcq's are based on the core syllabus but every ppr tends to have few tricky questions which tests both......if u had done only core it  would look gibberish bt havin dne extended it makes sense....... otherwise it be funny if a core dude got A in ppr 1 and 6......nd then couldnt go above C in pp3 lolzzz :P
 ;D ;D ;D
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Offline red_911

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Re: Chemistry doubt
« Reply #11 on: May 24, 2010, 10:39:13 am »
hey plzz anyone explain me question 13 pp1 O/N 2009  ???
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Offline Vin

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Re: Chemistry doubt
« Reply #12 on: May 24, 2010, 10:43:25 am »
Quote from: red_911 on May 24, 2010, 10:39:13 am
hey plzz anyone explain me question 13 pp1 O/N 2009  ???

which variant ??
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Offline red_911

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Re: Chemistry doubt
« Reply #13 on: May 24, 2010, 10:45:34 am »
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Offline Vin

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Re: Chemistry doubt
« Reply #14 on: May 24, 2010, 11:10:54 am »
Quote from: red_911 on May 24, 2010, 10:45:34 am
variant one

Ok remember when concentrated NaCl is electrolyzed:
First the solution contains Na+ Cl- and H+ and OH- (from water). The positive inos go to the cathode, and negative ions to the anode.

At the CATHODE
the H+ ions accept electrons, since it is less reactive than Na (always elements which is more reactive 'likes' to stay in the ionic form)
2H+  +  2e-  ---> H2

At the ANODE
the Cl- ions give up the electrons more readily than the OH- ions do.
2Cl-  -->  Cl2  +  2e-

what left in the solution is Na+ and OH- which combine to form NaOH

in your ques ..is 'D' .. the indicator solution turns blue at -ve as NaOH is produced .. Chlorine doesnt  show any change in presence of an indicator solution ;)

jus understand the concept ..

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