# Why is the pH level of carbonation loss decreasing then increases afterwards?

We have done an experiment of the titration of unsealed sprite soda to find the amount of carbonic acid being loss on various duration (0 to 1 hour), due to decrease pressure. The calculation was to determine the pH of carbonic acid overtime, thus the number of concentration of flat and unsealed soda are subtracted and is converted to pH level using -log[concentration of flat soda - unsealed soda].This was done multiple times on multiple duration until 1 hour. Now the results has demonstrated that carbonic acid pH level was decreasing in the first 30 minutes but then afterwards it was increasing. This contradicts on what my hypothesis is as it states that due to pressure being decreased (by unsealing the soda) the pH will increase turning more basic. Is this due to the factors of pressure and temperature? Can you please describe this thoroughly? Thank you for your time on reading this.

• Was that pH observation before the titration or after it ? – Poutnik May 21 at 18:47
• The pH observation was after the titration sir. – Jake Knight May 21 at 21:04
• Is not the pH computation ignoring citric acid content ? – Poutnik May 23 at 12:03
• Plus, is not it ignoring the strength of the carbonic acid ? – Poutnik May 23 at 12:48

## 1 Answer

At the beginning, there was titrated mostly just the citric acid and the equilibrium amount of carbonic acid.

After that, carbon dioxide slowly converted to carbonic acid and $$\mathrm{pH}$$ has been decreasing.

Finally, the long term process took dominance as dissolved carbon dioxide together with carbonic acid were leaving solution as gaseous carbon dioxide and $$\mathrm{pH}$$ have been raising.

• Sorry I haven't specified the description clearly, we have titrated both the flat soda (where all carbonation is loss) and the soda that is titrated in various duration. The amount of moles has been determined for both of the flat soda and the 'duration soda' and was subtracted, resulting the moles of only carbonic acid. This was then converted to pH level and was done multiple times for various duration. I am very sorry that I wasn't clear on this. – Jake Knight May 22 at 6:32
• You know, the prerequisite for good answers is a good question. If others have to guess, imagine or interpret what is the real question, answers are rarely what was wanted and clarification wastes resources on all sides. :-) – Poutnik May 22 at 6:42
• Converted to pH level ? I thought it was measured... Do you mean estimation of pH of sprite soda drink before and after titration ? The best would be, if you rewrite the question as a detailed description of experiment, with raising the clear questions about experiment details in a particular experiment stage. – Poutnik May 22 at 6:49
• I will do that. Thank you for your time – Jake Knight May 22 at 7:17