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Topic: Aspirin tablets  (Read 18444 times)

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Offline ARGOS++

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Re: Aspirin tablets
« Reply #15 on: January 18, 2008, 11:50:56 AM »

Dear Angelku;

Maybe? a little bit simpler:

That’s because for CaCO3 as an Example, and/at the given End Point:
   CaCO3     +  H2SO4  --->  CaSO4 +   H2O + CO2(g) .
 
And that would be quasi equivalent to:
    Ca(OH)2  +  H2SO4  --->  CaSO4 + 2H2O
(because CO2(g) has left the System.)

I hope it may be of help.


Good Luck!
                    ARGOS++

Offline AWK

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Re: Aspirin tablets
« Reply #16 on: January 18, 2008, 12:04:43 PM »
At ph 8 CO2 do not left the system!
AWK

Offline ARGOS++

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Re: Aspirin tablets
« Reply #17 on: January 18, 2008, 12:14:18 PM »
Dear Mr. AWK;

That’s precisely why I was also talking about Indicators and/at the given End Point: Not pH 8!
(Please see the previous posts.)

Good Luck!
                    ARGOS++

« Last Edit: January 19, 2008, 12:51:54 PM by ARGOS++ »

Offline AWK

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Re: Aspirin tablets
« Reply #18 on: January 18, 2008, 12:19:47 PM »
But Angelku use the phenol red indicator, and just its using practically prevents decomposition of CaCO3.
AWK

Offline ARGOS++

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Re: Aspirin tablets
« Reply #19 on: January 18, 2008, 12:32:31 PM »

Dear Mr. AWK;

I’m surprised!,  ─   Something below pH 6.6?:   "Phenol Red

Good Luck!
                    ARGOS++


Offline AWK

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Re: Aspirin tablets
« Reply #20 on: January 18, 2008, 12:42:01 PM »
When we titrate from basic side?
AWK

Offline ARGOS++

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Re: Aspirin tablets
« Reply #21 on: January 18, 2008, 02:18:24 PM »

Dear Mr. AWK;

Sorry!,  ─   Exactly in this case Phenol Red changes from Red to Yellow and so our Endpoint will lie at, or below pH 6.6!
(Not only Wiki is telling that.)

Good Luck!
                    ARGOS++


Offline angelku

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Re: Aspirin tablets
« Reply #22 on: January 18, 2008, 11:28:11 PM »
How about using phenolphthalein as an indicator?Its pH is 8.2-10.0.

Is is calcium carbonate in the solution have already completely decompose into CO2 which left to the system at pH below 7?Do you mean H2SO4 needed to be use for neutralising the additional amount of CO2 presence in the solution no matter the CO2 left or not?
I
Although the  CO2 leave the system at pH below 7,more amount of H2SO4 still needed to be used even the end point is at pH above 8.Am I right?
 ???

Offline ARGOS++

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Re: Aspirin tablets
« Reply #23 on: January 19, 2008, 06:22:49 AM »

Dear Angelku;

Cheer!,  ─   You are very Solomonic, and you learn quite fast/well, but how is it called in English (American):  “TANSTAAFL”.

If the CO2(g) from CaCO3 doesn’t leave the System, then also all the CO2(g) you picked up during hydrolysis, during dilution, and during titration will not leave the System either.
In such case you will find a too small value of H2SO4, now simulating a too high content of Aspirin!

Quintessence: 
You can’t make a method more specific as it is by its nature,   ─   You have to live with.
(But you can combine/change methods!)

Good Luck!
                    ARGOS++


Offline AWK

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Re: Aspirin tablets
« Reply #24 on: January 21, 2008, 07:35:23 AM »
How about using phenolphthalein as an indicator?Its pH is 8.2-10.0.

Is is calcium carbonate in the solution have already completely decompose into CO2 which left to the system at pH below 7?Do you mean H2SO4 needed to be use for neutralising the additional amount of CO2 presence in the solution no matter the CO2 left or not?
I
Although the  CO2 leave the system at pH below 7,more amount of H2SO4 still needed to be used even the end point is at pH above 8.Am I right?
 ???
I think phenolphtalein is a good idea. It change color (become colorlees) just 0.1 pH unit over pH of NaHCO3 hydrolysis
AWK

Offline ARGOS++

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Re: Aspirin tablets
« Reply #25 on: January 31, 2008, 05:11:41 PM »

Dear Mr. AWK;

I don’t understand:   ─   A good Idea?   ─   For what?

─  For the evidence that the CO2  will not leave the system and we titrate a more or less erroneous actual content?

─  Or that we Chemists are so genial that we are able to titrate with a visual precision of better then 0.1 pH Units with the help of an indicator with its well known problems at acidic end of its indication range?

I don’t believe that continuing such discussions are doing any good job/help for anybody who tries to learn,  ─  Sorry!

Good Luck!
                    ARGOS++


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