Problem 80 - Chemistry: An Atoms-Focused Approach

Question

Explain why different liquids do not reach the same height in capillary tubes of the same diameter.

Step-by-Step Solution

Answer

Answer: Different liquids do not reach the same height in capillary tubes of the same diameter due to differences in their surface tensions, wetting properties, and densities. These factors influence the strength of cohesive and adhesive forces, as well as the weight of the liquid column, ultimately determining the height reached within the capillary tube.

Step 1: 1. Understanding capillary action

Capillary action is the ability of a liquid to flow into narrow spaces without the assistance of gravity, or in opposition to it. This phenomenon occurs due to the interaction between the liquid's cohesive forces (which hold the liquid molecules together) and adhesive forces (which attract the liquid molecules to the walls of the capillary tube).

Step 2: 2. Factors affecting capillary rise

There are three main factors that affect the height a liquid reaches in a capillary tube: - Surface tension: Surface tension is the cohesive force holding the liquid's molecules together. The greater the surface tension, the stronger the cohesive forces, and the higher the liquid can rise in a capillary tube. - Wetting properties: The wetting properties of a liquid describe the adhesive forces between the liquid and the capillary tube's walls. Better wetting liquids will have a stronger attraction to the walls, resulting in a higher capillary rise. - Density: The density of a liquid determines the weight of the liquid column in the capillary tube. As the density increases, the weight of the liquid column also increases, resulting in a lower capillary rise.

Step 3: 3. Applying the factors to different liquids

Different liquids have different surface tensions, wetting properties, and densities. This leads to different heights reached within capillary tubes of the same diameter, as each liquid interacts differently with the walls of the tube and experiences different cohesive and adhesive forces. For example, water has a high surface tension and good wetting properties on glass, allowing it to rise relatively high in a glass capillary tube. On the other hand, oil has a lower surface tension and poorer wetting properties on glass, resulting in a lower capillary rise in the same tube.

Step 4: 4. Conclusion

To summarize, different liquids do not reach the same height in capillary tubes of the same diameter due to differences in their surface tensions, wetting properties, and densities. These factors dictate the strength of cohesive and adhesive forces experienced by the liquid, as well as the weight of the liquid column, ultimately determining the height reached within the capillary tube.