Message written with lemon juice appears when paper is treated with iodine solution.
name: Vitamin C prevents complex formation between iodine and starch.
In this experiment lemon juice developed by iodine solution is used to prepare invisible inks. When paper with written message is treated with iodine solution the starch contained in paper reacts with iodine to form a colored complex:
(C6H10O5)n + I2 → I2*(C6H10O5)n
The paper turns blue but the message still stays white. Lemon juice contains vitamin C which prevents the reaction between starch and iodine:
I2 + I- → I3-
C6H8O6 + I3- + H2O → C6H6O6 + 3I- + 2H+