IGCSE/GCSE/O & A Level/IB/University Student Forum
Qualification => Subject Doubts => IGCSE/ GCSE => Sciences => Topic started by: acash09 on May 22, 2010, 05:37:41 pm
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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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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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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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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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if u mean chemistry paper 3 ..yep!
LOL my bad :D
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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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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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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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Yes, apparently it is based on the core syllabus. :-\
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Yes, apparently it is based on the core syllabus. :-\
Isn't that a good thing ??? :o
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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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hey plzz anyone explain me question 13 pp1 O/N 2009 ???
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hey plzz anyone explain me question 13 pp1 O/N 2009 ???
which variant ??
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which variant ??
variant one
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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 ..
(http://content.answers.com/main/content/img/McGrawHill/Encyclopedia/images/CE221700FG0010.gif)
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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 ..
(http://content.answers.com/main/content/img/McGrawHill/Encyclopedia/images/CE221700FG0010.gif)
lol...Thanks alot ... but y does the indicator solution turns blue only at -ve electrodde and not the whole solution ?
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lol...Thanks alot ... but y does the indicator solution turns blue only at -ve electrodde and not the whole solution ?
good ques .. see in this question u hav to act smart .. i think i forgot to mention .. look at the options .. u now kno tht NaOH is produced so the indicator turns blue ..there are two options with 'bule/purple' A and B .. now see A .. at -ve 'red' is given which is not possible because no acid it produced during the reaction so u r left with D .. ;)
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hey, between which elements can you find carbon in the reactivity series ?! ???
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hey, between which elements can you find carbon in the reactivity series ?! ???
LEARN it ! ;)
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LEARN it ! ;)
:P i sure will! thank you ;D
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:P i sure will! thank you ;D
sure .. ;) your welcome
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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 ..
(http://content.answers.com/main/content/img/McGrawHill/Encyclopedia/images/CE221700FG0010.gif)
u said H2 goes to cathode , then y u said sodium hydroxide changes indicator to blue when it is at the bottom not even close to the +ve electrode
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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 ..
(http://content.answers.com/main/content/img/McGrawHill/Encyclopedia/images/CE221700FG0010.gif)
it isnt concentrated, its aqueous .!!!
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it isnt concentrated, its aqueous .!!!
AADI U GAVE ME AN ATTACK !! ITS CONCENTRATED AQ. NaCl
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hi By the way below copper theres mercury Hg
i have a question mj 04 p1 q 30
why is the answer C?
can sum1 explain plz
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hi By the way below copper theres mercury Hg
i have a question mj 04 p1 q 30
why is the answer C?
can sum1 explain plz
the original is dilute NaOH because it has water in it...so say its pH is 10 (>7, because its alkali)
the distillate is water so pH = 7
the NaOH in the flask doesnt have any water left, so its concentrates that means its pH >10 (dilute NaOH)
thus , C
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hey can you tell me what colour chnages occur when universal indicator comes in contact with
hydrogen
oxygen
ammonia
and i thought acid /salt added to UI would not change the colour of UI.
right?
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UI in neutral solutions is green
in alkali blue if weak, violet if strong
in acid red & u do not test for gases with UI
Thanks A@di :)
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hey can you tell me what colour chnages occur when universal indicator comes in contact with
hydrogen
oxygen
ammonia
and i thought acid /salt added to UI would not change the colour of UI.
right?
hydrogen - no change
oxygen - no change
ammonia - blue/purple
yes it does .. right click and click view image
(http://www.jirvine.co.uk/Chemistry_GCSE/C2b/Universal_indicator_1.JPG)
(http://www.bbc.co.uk/schools/ks3bitesize/science/images/universal_indicator.jpg)
(http://image.made-in-china.com/2f0j00tesEfqjbaacV/Universal-Indicator-Strips.jpg)
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hydrogen - no change
oxygen - no change
ammonia - blue/purple
yes it does .. right click and click view image
(http://www.jirvine.co.uk/Chemistry_GCSE/C2b/Universal_indicator_1.JPG)
(http://www.bbc.co.uk/schools/ks3bitesize/science/images/universal_indicator.jpg)
(http://image.made-in-china.com/2f0j00tesEfqjbaacV/Universal-Indicator-Strips.jpg)
umm this means phenolphthalein is not an UI?
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Ofc not , just another indicator
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umm this means phenolphthalein is not an UI?
No it isnt.