Disappearing ink

Diffusion is the net movement of a substance from a region of high concentration to a region of low concentration. This is also referred to as the movement of a substance down a concentration gradient (change in the value of a quantity). Ink is a liquid that contains pigments, dyes and solvents and when added to cold water it start to spread and water change color (diffuson). In a worm water diffusion progress faster because molecules have more enegry and the space between them is grater. Pigment contained in ink have another attribute (thanks to polar covalent bonds). In warm wter it looses his color and when the solution is cooled the color is restored.

Covalent bonds with unequal electron sharing are called polar covalent bonds. The atom with the higher electronegativity will have a greater share of the electrons. This will result in the atom having a slight negative charge compared to the other atom which will have a slight positive charge.