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31.19 What is the pH of Coca-cola?




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This article is from the Chemistry FAQ, by Bruce Hamilton B.Hamilton@irl.cri.nz with numerous contributions by others.

31.19 What is the pH of Coca-cola?

Phosphoric acid is an approved food-grade acid that is added to Coca-cola
to provide some of the taste. When CO2 is added to "carbonate" aqueous
solutions, carbonic acid is formed. A tin of coca-cola was cooled in a
refrigerator to 7C and the pH of the sample measured over time. The pH
electrode was not temperature-compensated, so a correction was applied.

  Time              pH                pH
               (when opened)     (corrected)            
Initial          2.75 @ 7C           2.6
30 seconds       2.78 @ 7C           2.6
60 seconds       2.80 @ 7C           2.6
2 minutes        2.82 @ 7C           2.7
4 minutes        2.80 @ 7C           2.6

A sample was degassed in an ultrasonic bath for several minutes and the
pH measured, and compared to a control sample maintained at the same
temperature and time profile.

                    pH
Degassed pH      2.52 @ 21c
RT sample        2.50 @ 20C

So the conclusion is that the pH of Coca-Cola is approximately 2.5 - 2.7.
Not surprisingly, the relatively weak carbonic acid from the dissolved CO2
did not significantly affect the pH of the beverage. The aluminium beverage
containers are lined with a thin polymer or lacquer coating to prevent the
aluminium metal dissolving into the beverage.

Note that the differing flotation characteristics of cans of the normal
versions of carbonated beverages like Coca-Cola ( they may sink ), and
the diet versions ( they may float ), has nothing to do with the amount
of CO2 present. It is due to the increase in solution density from the
few percent of sugar added to the normal version, while the diet version
has only a few hundred ppm of an artificial sweetener that is much sweeter
than sugar.

 

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