Soluble means able to dissolve in a liquid. When something is soluble, it breaks apart and mixes completely into a liquid until you can't see it anymore, like sugar disappearing into hot tea or salt vanishing into water.

Scientists use this word to describe how different substances behave in liquids. Table salt is highly soluble in water: it dissolves quickly and completely. Sand, on the other hand, is insoluble: no matter how much you stir, it just sinks to the bottom. Some things are only slightly soluble, meaning a little bit will dissolve but the rest won't.

Temperature matters: sugar becomes more soluble in hot water than in cold, which is why it's easier to sweeten hot chocolate than iced tea. Different liquids matter too: oil paint is soluble in turpentine but not in water.

The opposite of soluble is insoluble. When a chemistry teacher asks if a substance is soluble, she wants to know whether it will dissolve or just sit there. Understanding solubility helps explain everyday mysteries: why soap works to clean dishes, why some medicines dissolve under your tongue, or why that powdered drink mix needs stirring to blend into your water bottle.