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Very IMPORTANT - Polish Chemistry competition, please help

Very IMPORTANT - Polish Chemistry competition, please help - Chemistry Forum

Very IMPORTANT - Polish Chemistry competition, please help - Chemistry Forum. Discuss chemical reactions, chemistry.


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  #1  
Old 01-28-2004, 06:04 PM
Bebop
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Default Very IMPORTANT - Polish Chemistry competition, please help



Hello!
I live in Poland. I attend here the last class of junior high (a
secondary school - I'm 16 years old). I've got many interests and
Chemistry is one of them.
That's why I took part in a Polish Chemistry competition organised for
people of my age. I got through to the second round aswell as my
school mates (11 students), mostly because of the support of the
greatest teacher ever (no one teaches Chemistry like she does).
The second round was organised on the beggining of this year (10th
January). Before it everyone had been sure of getting through to the
final, we were studying whole days & nights.
After the comp we were curious of one excercises. Most of us had the
same solution, so we thought it was OK.
Few days later, our teacher told us that none of us worked this
excercise well...
The comitee suggested really strange solution, no one got the idea and
most of the people writting the second round didn't get through (99%
:evil: ). Saying that differently - in the final there will probably
be 10 students out of aprox. 500...

Now what I want to ask you to do... We want to write to the comitee to
cancel this controversial task, because of the very strange solution
suggested and no good solutions from the students.
In order to do this we need good reasons. That's why I ask YOU to sit
and try to solve this task. Please, it will be very helpful for me
and my friends.

The suggested solution will be provided in the nearest future .

Task:
'The admixture of natrium's hydroxide (NaOH) in natrium's carbonate
(Na2CO3) can be detected in the following way : dissolve the sample
of the carbonate (Na2CO3) in water (H2O), then add dilution (I'm not
sure if it's understandable in English- otherwise spirit is OK?) of
BaCl2 in excess and few drops of
indicator showing if the dilution is basic (colourising the dilution
in kind of pink - I don't what's the name of this indicator in
English so I'm trying to describe it, in Polish it's
'fenoloftaleina'). The appearence of the pink color proclaim that
there's admixture of NaOH in Na2CO3. Explain with reaction's
equations and explaination in words this way of detection NaOH's
admixture in Na2CO3.'

Inform me if anything is not understandable, cos it's the first time I
use the chemical vocabulary .



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  #2  
Old 01-28-2004, 06:16 PM
G. R. L. Cowan
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Default Very IMPORTANT - Polish Chemistry competition, please help

Bebop wrote:

Phenolphthalein.


The barium cations will drop the carbonate anions.


--- Graham Cowan
[Only registered users see links. ] --
"Boron: A Better Energy Carrier than Hydrogen?"
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  #3  
Old 01-29-2004, 03:50 AM
Barry
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Default Very IMPORTANT - Polish Chemistry competition, please help

<snip>
Barium chloride solution precipitates the carbonate ion, leaving what is
effectively a neutral solution of sodium chloride. Any sodium hydroxide
present in the original sodium carbonate will be left in solution, and (if
there's enough of it) will cause phenolphthalein solution to become pink.

Hope this is clear

Barry Hunt


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  #4  
Old 01-29-2004, 09:00 PM
Bebop
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Default re:Very IMPORTANT - Polish Chemistry competition, please help

This is how it was described by the judging comitee:
- dissolving Na2CO3 + 2 H2O -->2 NaOH + H2O + CO2 (1 point)
- BaCl2 + H2O + CO2 -->BaCO3(solid)+ 2 HCl (1 point)
- neutralizing base 2 NaOH + 2 HCl -->2 NaCl + 2 H2O (1 point)
- reason why the solution colorises with phenophtalein: excess of
sodium hydroxide (NaOH)
in the sample of Na2CO3 that wasn't neutralized by created acid causes
the appearance
of the pink color in the solution. (2 points)
TOTAL: 5 points

Please tell me what you think about it .
Big thanks for your interest .



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  #5  
Old 01-29-2004, 10:56 PM
Barry
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Default re:Very IMPORTANT - Polish Chemistry competition, please help


"Bebop" <[Only registered users see links. ]-spam.invalid> wrote in message
news:40197484$1_1@127.0.0.1...

That is a weird way of looking at it!! The first reaction (generating CO2)
is not realistic.

The overall reaction is:

Ba++ + CO3-- >> BaCO3 (insoluble)
leaving equivalent numbers of Na+ and Cl- ions, hence neutral solution.
Any NaOH present, is almost entirely Na+ and OH-.
OH- reacts with phenolphthalein to give the characteristic red colour.

I can't understand what your instructors are trying to achieve by expressing
it the way they have.

Barry


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  #6  
Old 01-30-2004, 06:01 AM
friend®
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Default Very IMPORTANT - Polish Chemistry competition, please help

On 29 Jan 2004 15:00:52 -0600, [Only registered users see links. ]lid
(Bebop) wrote:


bzdura, sprawdzcie wykres w Chemii Analitycznej Minczewskiego i
Marczenki, w moim wydaniu na stronie 87. Wolny CO2 bedzie obecny od pH
7.2 w dol.
Nie ma mowy o jedneczesnej obecnosci NaOH i CO2.


bzdura, chlorek barowy jest niemal calkowicie zdysocjowany, wiec
powinno sie pisac Ba2+ + CO3(2-)-> BaCO3
w zaleznosci od obecnosci lub nie wodorotlenku, weglan po
rozpuszczeniu tworzy jony weglanowe ew. takze wodoroweglanowe (gdy
NaOH jest nieobecny).
fenoloftaleina zmienia barwe w zakresie 8.4-9.4. w zaleznosci od
stezenie, czyli nawet mieszanina weglanu i wodoroweglanu spowoduje
zmiane, bez watpienia sam weglan takze. To znaczy, ze chlorek barowy
stracajac weglan bedzie utrzymywal niskie pH (bezbarwny roztwor) do
czasu, gdy chlorek barowy pozostaje w nadmiarze. W momencie gdy
zostanie zuzyty, wtedy pH podskoczy i fenoloftaleina ulegnie
zabarwieniu. To sie stanie nawet bez obecnosci wodorotlenku, chociaz
jego obecnosc przyspieszy te zmiane.
Caly wstep z cytowanej ksiazki ma tu zastosowanie.


Kto organizowal te olimpiade? SLD dla dzieci swoich czlonkow?

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  #7  
Old 01-30-2004, 09:33 AM
Mohammed Farooq
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Default Very IMPORTANT - Polish Chemistry competition, please help

fkasner <[Only registered users see links. ]> wrote in message news:<c%fSb.6079$[Only registered users see links. ].prodigy.c om>...



A similiar example of absurd equation was given in our grade nine
Pakistani textbook ( fortunately they changed the book after remaining
in print for atleast five years) describing sodium chloride soluion
is "neutral" because of the reaction : NaCl + H2O ----> NaOH + HCl !!!
I don't know from where the authors (two of them were Ph.Ds) copied
it?
Mnay other phosphorus compounds of sulfur were shown in reaction
equations, which had never been reported to exist!



Aren't these equations illogical to describe precipitation of barium
carbonate by sodium carbonate?
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  #8  
Old 01-30-2004, 12:59 PM
Bebop
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Default re:Very IMPORTANT - Polish Chemistry competition, please help

To friend :
Komisja Konkursu Chemicznego dla uczniów gimnazjum .
Chcemy napisac odwolanie bo nikt nie
rozwiazal tego zadania tak jak oni to sugeruja... Nawet nauczyciele,
co dopiero uczniowie :P.
10 osób ledwie do finaBu przechodzi na 500, bo mialo maksa z
innych rzeczy :P. Pisa takie olimpiady na 100 % ?? No bez
przesady.



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  #9  
Old 01-30-2004, 01:14 PM
friend®
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Default Very IMPORTANT - Polish Chemistry competition, please help

sprobujcie skontaktowac sie z Wydzialem Chemii Uniwersytetu
Warszawskiego, mysle ze jeszcze paru myslacych tam zostalo.
Preferowane rozwiazanie, nie jest prawidlowe ani teoretycznie, ani
praktycznie.



On 30 Jan 2004 06:59:20 -0600, [Only registered users see links. ]lid
(Bebop) wrote:


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