MadSci Network: Chemistry |
Any solution of base will lose pH over time if it is exposed to air. Air contains carbon dioxide; carbon dioxide dissolves in water to give carbonic acid; carbonic acid reacts with base to form carbonate. Indicators which change at a relatively high pH (like phenolphthalein, which changes around pH 9) will "go acidic" on exposure to atmospheric CO2. The heat from the lamp probably hastens the reaction. Dan Berger
Try the links in the MadSci Library for more information on Chemistry.