Re: does the concentration of citric acid change in lemon juice overtime?

Dear Shwetha,

It certainly seems unlikely that citric acid will break down in lemon juice over the timeframe of five days which you describe. However, if an aqueous solution containing citric acid were left open to the air over five days, evaporation would certainly become an issue. As the water evaporates, the concentration of citric acid in the lemon juice would increase. As the pH of a solution is dependent upon the concentration of the acid in solution, this would have the effect of lowering the pH. Precisely how much is going to depend upon the total volume of lemon juice you started with and the rate of evaporation, which is influenced by the heat of the surrounding environment and the total surface area exposed to the air, etc. Hence, one way to test this would be to measure the pH of your lemon juice over a period of five days.