Diffusion. Potassium permanganate (KMnO4, purple) crystals dissolving in water. As the potassium permanganate dissolves it diffuses throughout the water forming a solution. Diffusion is caused by the tiny, random movements of molecules in a solution. Over a period of time these movements cause the dissolved substance to become evenly dispersed throughout the solvent. The potassium permanganate will eventually produce a uniform purple solution without being stirred.