Abstract
We describe here an activity that enables students to visualize the dissolution process, ion mobility, and precipitation on a microscale level, all in 30 s. A small puddle of water consisting of approximately 10 drops is placed on a plastic sheet cover. Two small crystals of water-soluble salts are transferred by toothpicks and simultaneously introduced to the puddle from opposite sides. Within 30 s, a precipitate forms where the two ionic solutions meet and the result usually looks somewhat like a cat's eye marble. A significant feature of this activity is that it uses a minimum amount of resources.