Definition and meaning of Capillary Action in chemistry.
Two different molecular forces fight against each other to create this upward climbing effect. The first force is adhesion, which is the strong attraction between the liquid and the solid surface. The second force is cohesion, which is the natural attraction the liquid molecules have for each other.
Capillary action happens when the adhesive forces are much stronger than the liquid’s cohesive forces. The strong adhesion causes the liquid molecules to rapidly grab onto the walls of the tube. This climbing motion creates a curved liquid surface that chemists call a concave meniscus.
The liquid climbs the walls while surface tension smoothly pulls the deeper liquid up behind it. The physical width of the tube directly decides exactly how high the liquid can travel. The upward pulling force only happens exactly along the inner edge of the solid tube.
A very narrow tube has less empty space in the middle to weigh the rising liquid down. Therefore, a liquid will always rise much higher in a thin tube than in a wide glass. Scientists use a mathematical formula called Jurin’s law to predict exactly how high the liquid will go.
ExampleYou can safely stick a very thin glass capillary tube directly into a small cup of water. The water molecules are highly attracted to the glass, so adhesion easily wins against cohesion. The water will quickly creep up the inside of the narrow glass tube against gravity. The water stops rising when its own heavy weight finally equals the upward pulling force.
Does capillary action work with heavy liquid mercury?
Mercury actually shows the complete opposite effect. Its own cohesive forces are much stronger than its attraction to glass. Mercury will push itself down inside a glass tube and form a curved bump.
Why does a narrower tube cause a greater upward rise?
The lifting force only pulls along the outer edge where the liquid touches the glass. A wide tube has too much heavy water in the middle for the edges to lift. A narrow tube has less heavy water, so it lifts much higher.
How do trees use capillary action?
Trees use this force to pull water from their roots up to their highest leaves. The inside of a tree contains thousands of microscopic wooden tubes called xylem. Water climbs these tiny tubes to keep the tree alive.
