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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: kuromi on May 11, 2009, 07:25:05 AM

Title: [hurry] citric acid reacts with sodium hyoxide !!!!
Post by: kuromi on May 11, 2009, 07:25:05 AM

C6H8O7 (aq)  +  OH- (aq)    :rarrow:      C6H7O7- (aq)  +  H2O(l)

OR C6H8O7 (aq)  +  3OH- (aq)     :rarrow:     C6H5O7 3- (aq)  +  3H2O(l)

Which one is correct ??   
Title: Re: [hurry] citric acid reacts with sodium hyoxide !!!!
Post by: Borek on May 11, 2009, 07:33:24 AM
Both, plus

C6H8O7 +  2OH- :rarrow: C6H6O72- + 2H2O

Depends on what you are asking (or are asked) about.
Title: Re: [hurry] citric acid reacts with sodium hyoxide !!!!
Post by: kuromi on May 11, 2009, 07:39:35 AM
Both, plus

C6H8O7 +  2OH- :rarrow: C6H6O72- + 2H2O

Depends on what you are asking (or are asked) about.


 to determine the Ka and pKa of 0.1M citric acid !! 
at 296 K , 20cm^3  of 0.1M citric acid titrate with 0.1M sodium hyoxide until end pt.
then , add a further 20cm^3  of  the same acid 
the pH of the mixture is 4.45  and used 62.7 cm^3 of sodium hyoxide  ~~~
Title: Re: [hurry] citric acid reacts with sodium hyoxide !!!!
Post by: Borek on May 11, 2009, 07:57:33 AM
to determine the Ka and pKa of 0.1M citric acid !!

pKa1, pKa2 or pKa3?

Quote
at 296 K , 20cm^3  of 0.1M citric acid titrate with 0.1M sodium hyoxide until end pt.

Just out of curiosity - how do you determine end point?

Quote
then , add a further 20cm^3  of  the same acid 
the pH of the mixture is 4.45  and used 62.7 cm^3 of sodium hyoxide  ~~~

What will you have in the solution at this point?

Think about stoichiometry of the neutralization reaction. You already known citric acid is triprotic.
Title: Re: [hurry] citric acid reacts with sodium hyoxide !!!!
Post by: kuromi on May 11, 2009, 08:11:41 AM
this is 

to determine the Ka and pKa of 0.1M citric acid !!

pKa1, pKa2 or pKa3? --- > i dont know , lab sheet is just to ask the pKa !!

i used phenolphthalein --> end pt : colourless to pink

the pH of the mixture is 4.45  and used 62.7 cm^3 of sodium hyoxide for titration, 

which are my experimental results !!   


Title: Re: [hurry] citric acid reacts with sodium hyoxide !!!!
Post by: Arkcon on May 11, 2009, 08:21:37 AM
So, when the solution turns pink, what does that mean?  Is there any acid left?  What would it mean, to a citric acid molecule, if it had no acid left?  What is acid, anyway?
Title: Re: [hurry] citric acid reacts with sodium hyoxide !!!!
Post by: Borek on May 11, 2009, 08:26:31 AM
lab sheet is just to ask the pKa !!

No such thing as just pKa of the citric acid. It has to be one of the three.