The negative areas of the water molecules surround the positive sodium ions. As the attractions from the water molecules and their motion pulls the ions apart, the sodium chloride crystal dissolves.

Students investigate the polarity of the water molecule and design tests to compare water to less polar liquids for evaporation rate, surface tension, and ability to dissolve certain substances.

Heat can help some substances dissolve faster in water. Salt, for example, will dissolve quicker in hot water than in cold water. When a substance dissolves, it might look like it has disappeared ...