Discussionontheshapeofthespritetitrationcurve[1]

Discussionontheshapeofthespritetitrationcurve[1] - should...

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Discussion on the shape of the sprite titration curve; Observe from your calculations that the molarity of the sprite is very low(7x10-3 mol/L). At this concentration, the acid is most probably completely dissociated and is already a buffer. This is one reason for not observing a sharp rise. Instead, you observe a continuous rise in pH through out. There are three different buffer system, two of them being quite acidic. This should account for the linearity of the curve. There is only one rise instead of the expected three. Why? One obvious reason is the fact that the pKa’s are quite close and with the shape of the curve being almost linear you would observe the expected small rise. The rise is definitely from the third pKa and not the first two. How can one be sure of this? Since the third pKa is around 6, this rise due to the loss of the third proton should definitely be before a pH of 10. In the case of coke, the third pka
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Unformatted text preview: should be around 13 and this would not be observed since the pH of the diluted NaOH is around this value. This is not the case here. Also, if the continued the titration till we have doubled the volume of NaOH after the observed first equivalence point, we would not observe a second rise. Hence the observed rise should be due to the loss of the third proton. Does the presence of small amounts of sodium citrate and sodium benzoate affect the shape of the curve? Doubtful. How can one confirm this? Run a titration curve with solid citric acid. The curve is similar. If one runs the titration with a suitably high concentration of citric acid, one should be able to see an initial sharp upward rise due to the presence of buffer chemicals, but the curve will have only one significant rise due to the loss of the third proton and the first two rises will not be seen....
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