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Author Topic: Chemistry Practical  (Read 3918 times)

Offline @d!_†oX!©

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Chemistry Practical
« on: October 26, 2009, 04:51:09 am »
If we are given this test in the qualitative analysis for salts :
" Place the funnel in a test-tube.
Pour about 3 cm3 of dilute nitric
acid onto the residue contained
in the funnel. Add about 2 cm3 of
potassium iodide to the solution
collected in the tube. "

How does it show that the salt is lead carbonate???
even the mark scheme only says : " fizz / bubbles / effervescence "
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Offline Ghost Of Highbury

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Re: Chemistry Practical
« Reply #1 on: October 26, 2009, 05:08:23 am »
can u plz tyoe in the year of the Qp..and all other details..
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Offline @d!_†oX!©

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Re: Chemistry Practical
« Reply #2 on: October 26, 2009, 05:14:00 am »
its from May/June 2007 [ http://www.freeexampapers.us/IGCSE/Chemistry/CIE/2007%20Jun/0620_s07_qp_5.pdf ] page no. 4
and By the way one more thing
in the question paper the c) part is for 2 marks and d) part is also 2 marks
bt the mark scheme says c) part is 1 mark and d) part is 3 marks...
so can that happen in any question with us..as in can they change the marks at any point of time even after our papers are over....???
and is the test for lead in our syllabus???i have only seen it in this particular paper...its not even there in th data sheet provided to us "Notes for qualitative analysis"
plss urgent help required guys!!!!!!!
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Offline Ghost Of Highbury

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Re: Chemistry Practical
« Reply #3 on: October 26, 2009, 05:27:15 am »
Quote from: @d!_†oX!© on October 26, 2009, 04:51:09 am
If we are given this test in the qualitative analysis for salts :
" Place the funnel in a test-tube.
Pour about 3 cm3 of dilute nitric
acid onto the residue contained
in the funnel. Add about 2 cm3 of
potassium iodide to the solution
collected in the tube. "

How does it show that the salt is lead carbonate???
even the mark scheme only says : " fizz / bubbles / effervescence "

idoide salt = yellow ppt.
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Offline @d!_†oX!©

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Re: Chemistry Practical
« Reply #4 on: October 26, 2009, 05:28:37 am »
why iodide????
there is no yellow ppt...
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Offline Ghost Of Highbury

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Re: Chemistry Practical
« Reply #5 on: October 26, 2009, 05:32:48 am »
Quote from: @d!_†oX!© on October 26, 2009, 05:28:37 am
why iodide????
there is no yellow ppt...


lead iodide...(yellow)
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Offline xXFaKeXx

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Re: Chemistry Practical
« Reply #6 on: October 26, 2009, 05:40:02 am »
It has to be carbonate bcoz of the fizz produced on de addition of an acid.

But where da hell did lead come frm!!!!!!!
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Offline @d!_†oX!©

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Re: Chemistry Practical
« Reply #7 on: October 26, 2009, 05:41:46 am »
adi see...u didn't get my question  i think
according to the markscheme there is effervescence
and u r getting a yellow ppt cuzz of the potassium iodide dt u hv added nd not in d salt
and about the anions....i know dt it is carbonate [effervescence ]
but how do we find the cation???
there is no test for lead in the notes given to us by CIE
and acc. to d ms...the salt is lead carbonate..bt i dont understand how????

that's exactly my question fakex
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Offline xXFaKeXx

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Re: Chemistry Practical
« Reply #8 on: October 26, 2009, 05:45:40 am »
Okay here's da test for lead>>>>
a)Add dilute sodium hydroxide solution to a solution of the substance.   White precipitate, that does dissolve as more sodium hydroxide is added.

b)Add dilute ammonia solution to a solution of the substance.              White precipitate that does not dissolve as more ammonia is added.

Whereas NaOH and NH3 solution hav nt even been used in the question!
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Offline @d!_†oX!©

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Re: Chemistry Practical
« Reply #9 on: October 26, 2009, 05:47:50 am »
even i know the test now....i saw it in the A levels section sm1 had posted it
bt again nothing of this sort has been done!!!!!
what to do??? :o
fakex do u remember this is the same question that cam for our preboards...
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Offline xXFaKeXx

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Re: Chemistry Practical
« Reply #10 on: October 26, 2009, 05:49:01 am »
Yes i do remember dat test. I just scored 29.5 on 40.
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Offline Ghost Of Highbury

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Re: Chemistry Practical
« Reply #11 on: October 26, 2009, 05:49:38 am »
Quote from: @d!_†oX!© on October 26, 2009, 05:41:46 am
adi see...u didn't get my question  i think
according to the markscheme there is effervescence
and u r getting a yellow ppt cuzz of the potassium iodide dt u hv added nd not in d salt
and about the anions....i know dt it is carbonate [effervescence ]
but how do we find the cation???
there is no test for lead in the notes given to us by CIE
and acc. to d ms...the salt is lead carbonate..bt i dont understand how????

that's exactly my question fakex

ok..1st...potassium iodide is not YELLOW!!..it is WHITE in color..
u do no get the yellow ppt because of the potassium iodide..

2nd. i aint appearing for this exam..i am writing chem/6..but still..i think ewn u heat C...a white ppt and ____carbonate is left...

wen u leave the tube to cool..it appears black/grey (possibly)...and lead carbonate is also grey...but i'm still not 100% sure.
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Offline @d!_†oX!©

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Re: Chemistry Practical
« Reply #12 on: October 26, 2009, 05:54:00 am »
Quote from: | am | on October 26, 2009, 05:49:38 am
ok..1st...potassium iodide is not YELLOW!!..it is WHITE in color..
u do no get the yellow ppt because of the potassium iodide..

2nd. i aint appearing for this exam..i am writing chem/6..but still..i think ewn u heat C...a white ppt and ____carbonate is left...

wen u leave the tube to cool..it appears black/grey (possibly)...and lead carbonate is also grey...but i'm still not 100% sure.
@ adi
1st...i know potassium iodide is WHITE....wat i said is that wen u add it to th solution...the IODIDE ions in d sol. give the YELLOW ppt...
2nd....i knw ur not appearing for p5....nd i think u might be right at this
but is there anyone who is damn sure of any answer????
@fakex...oh yeah...al of us did badly in it man!!!
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Offline Ghost Of Highbury

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Re: Chemistry Practical
« Reply #13 on: October 26, 2009, 05:56:11 am »
Quote from: @d!_†oX!© on October 26, 2009, 05:54:00 am
@ adi
1st...i know potassium iodide is WHITE....wat i said is that wen u add it to th solution...the IODIDE ions in d sol. give the YELLOW ppt...
2nd....i knw ur not appearing for p5....nd i think u might be right at this
but is there anyone who is damn sure of any answer????
@fakex...oh yeah...al of us did badly in it man!!!

okk..cool..maybe some1 can correctly answer it..
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Offline @d!_†oX!©

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Re: Chemistry Practical
« Reply #14 on: October 26, 2009, 05:57:32 am »
Quote from: | am | on October 26, 2009, 05:56:11 am
okk..cool..maybe some1 can correctly answer it..
thanks for trying though!!! :) :)
plsss some1!!!!come to our rescue!!!!!! :P
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