Question

The rise of a liquid in capillary tube is due to (a) viscosity (b) osmosis (c) diffusion (d) surface tension

Short answer

The phenomenon that causes a liquid to rise in a capillary tube is (d) surface tension.

Step-by-step solution

Identify the Correct Phenomenon

A liquid rises in a capillary tube due to a phenomenon known as capillary action or capillarity. This is an instance where the surface of the liquid is in interaction with a solid, leading the liquid to climb up the walls of the solid against the direction of gravity.

Evaluate Options to Identify the Phenomenon

Now we are required to match this phenomenon with the given options, which are viscosity, osmosis, diffusion, and surface tension. Osmosis is the flow of solvent from an area of lower solute concentration to an area of higher solute concentration through a semipermeable membrane, which is not happening here. Similarly, diffusion is the movement of particles from an area of higher concentration to an area of lower concentration, again not applicable here. Viscosity refers to a liquid's resistance to flow, it doesn't result in the rise of liquid inside a capillary tube.

Confirm the Correct Option

The last remaining option is surface tension. Indeed, capillary action is a manifestation of surface tension. Surface tension is the property of a liquid, due to its intermolecular forces, that allows it to resist an external force. In the case of capillary action, the adhesion of the liquid to the walls of the capillary and the liquid's own cohesion pull the liquid up until there's a balance with gravity

Key concepts

Capillary Action

Capillary action is an intriguing phenomenon where a liquid rises or falls in a thin tube, such as a capillary tube, due to the interplay of cohesive and adhesive forces. This effect occurs when the adhesive forces between the liquid and the walls of the tube are stronger than the cohesive forces within the liquid. The liquid rises against gravity until these forces reach equilibrium. For example, when you place a narrow tube into water, the water climbs up the tube. This occurs because water molecules adhere to the glass more strongly than they adhere to each other, pulling the water upward. The height to which a liquid climbs in a capillary tube can be influenced by several factors:

• Diameter of the tube: Smaller diameters result in higher rise.
• Type of liquid: Different liquids have varying surface tensions.
• Contact angle: The angle between the liquid's surface and the tube wall, influencing adhesive force strength.

Capillary action is essential in many natural and technological processes, including the movement of water in plants and ink within a pen.

Viscosity

Viscosity is a measure of a liquid's resistance to flow. Imagine trying to pour honey and water from separate jars. Honey, which is more viscous, flows much slower than water. This property is essential in determining how substances behave under different conditions. The higher the viscosity, the thicker the liquid, leading to slower flow. Viscosity depends on:

• Temperature: Heating a liquid typically reduces its viscosity.
• Molecular structure: Larger or more complex molecules generally increase viscosity.

Viscosity is crucial in everyday applications, from motor oil being optimized for engines to blood circulation in the human body, ensuring that fluids move efficiently through different environments.

Osmosis

Osmosis is the process where water moves across a semipermeable membrane from an area of lower solute concentration to higher solute concentration. Imagine two containers separated by a semipermeable membrane, with one side containing more salt. Water will naturally move to the saltier side to balance concentrations. Key points about osmosis include:

• Semipermeable membranes allow the solvent (e.g., water) but not solutes (e.g., salt) to pass through.
• It is a crucial process in biological systems, such as nutrient and waste transport in cells.
• Osmosis can cause cells to shrink or swell depending on the surrounding solution's concentration.

Osmosis helps maintain a stable environment within living organisms, contributing to various biological processes that are vital for life.

Diffusion

Diffusion is the natural movement of particles from an area of higher concentration to an area of lower concentration, leading to an even distribution. Consider how the scent of a perfume spreads in a room. This occurs because the perfume molecules disperse into the air until they are evenly distributed. Several factors affect diffusion:

• Temperature: Higher temperature increases kinetic energy, speeding up diffusion.
• Molecule size: Smaller molecules diffuse faster than larger ones.

Diffusion is an essential process in biology, chemistry, and physics, facilitating processes like gas exchange in lungs or nutrient absorption in intestines. It is a passive process, meaning it doesn’t require energy input, and is fundamental for maintaining homeostasis in living organisms.