Lake Lianna is fed by two rivers, the Matthew and the Andrew. You have made careful water chemistry measurements throughout the year and found that the two rivers have the following pH and alkalinity:
Matthew River: pH = 8.2; alkalinity = 10-3 equivalents/liter
Andrew River: pH = 5.7; alkalinity = 10-5 equivalents/liter.
Your studies of river fluxes show that Lake Lianna is formed by mixing 2 parts of the Matthew with 3 of the Andrew. Calculate its pH, assuming that Lake Lianna is equilibrated with the atmosphere. Your measured pH value for Lake Lianna is 7.6. Why might this differ from the value you calculate based on mixing of the two sources?