1. # Does pH Go with the Fizz?

What happens to unfinished soda? Many soft drinks are easy to tell apart by their tastes; they all are made from different recipes. But what they have in common is the presence of carbon dioxide. Compare the original acidity of soda with what happens to pH levels as the soda loses its carbonation and goes “flat”.

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Carbon dioxide is found in many soft drinks. It is to carbon dioxide they owe their name - “sodas” or “soda”, for short.  In the manufacture of soda, the basic drink is saturated with carbon dioxide (CO2), which is added to the bottle under pressure. Carbon dioxide gives the drink a refreshing property. In addition, it is a preservative and a disinfectant of drinks due to its ability to inhibit the growth of microorganisms.

The disinfecting effect of carbon dioxide is increased by lowering the acidity level, the pH, of soda. This is because carbonic acid Н2СО3 is formed by the interaction of CO2 with water.

$\mathsf{CO_2 \cdot H_2O_{(p)} \rightleftarrows H_2CO_{3(p)} }$ (carbonic acid)

Then, carbonic acid dissociates: Н2СО3 → Н+ + НСО3,  releasing the H+ ions responsible for the lowering the pH of soda drink.  [WHY IMPROVES DISINFECTIVE ABILITY?]

The above reaction can go both ways; which way it goes depends on the gas pressure. When you open a sealed bottle or a can of soda, the pressure drops, and carbonic acid, Н2СО3 , decomposes into water and carbon dioxide.

This means that the pH of soda should keep changing as the gas (CO2) exits from the liquid.

In this project we will study how the pH of an open bottle or a can of soda changes over time after opening. We will be able to compare changes in the pH of various soda drinks after opening of the bottle or can in which it was stored.