Question

Surface tension of a liquid is found to be influenced by (A) It increases with the increase of temperature. (B) Nature of the liquid in contact. (C) Presence of soap that increase it. (D) Its variation with the concentration of the liquid.

Short answer

The correct statements about the influence of surface tension are: - Statement B: Surface tension is influenced by the nature of the liquid in contact. - Statement D: Surface tension varies with the concentration of the liquid.

Step-by-step solution

Statement A: Increases with the increase of temperature.

Generally, surface tension decreases with the increase of temperature. This is because at higher temperatures, the molecules in the liquid have more kinetic energy and are moving faster, thus reducing the cohesive forces among them. So, statement A is not true.

Statement B: Nature of the liquid in contact.

Surface tension is indeed influenced by the nature of the liquid in contact. Different liquids have different molecular structures and properties, which in turn affect the cohesive forces among the molecules. This means that surface tension can vary depending on the liquid and the substances in contact with it. So, statement B is true.

Statement C: Presence of soap that increases surface tension.

The presence of soap, or any surfactant, actually decreases surface tension. A surfactant is a substance that reduces the cohesive forces between molecules at the surface of a liquid. This is why soaps and detergents help to clean surfaces by reducing the surface tension of water, allowing it to spread more easily and mix with other substances. So, statement C is not true.

Statement D: Variation with the concentration of the liquid.

Surface tension can indeed vary with the concentration of the liquid. As the concentration of a liquid increases, its surface tension may also increase. This is because the number of molecules per unit area at the surface increases, leading to stronger cohesive forces. So, statement D is true. In conclusion, the accurate statements about the influence of surface tension are: - Statement B: Nature of the liquid in contact. - Statement D: Variation with the concentration of the liquid.

Key concepts

Temperature effect on liquids

Temperature can greatly impact the properties of liquids, including surface tension. As temperature increases, the surface tension of a liquid typically decreases. This can be attributed to the increase in kinetic energy of the molecules which makes them move faster. When molecules move more rapidly, they tend to spread apart. This weakens the cohesive forces that hold them together. As a result, the surface tension lessens because less force is needed to separate the molecules at the surface.

It's important to understand that the behavior of molecules at different temperatures plays a crucial role in the surface tension of liquids. Therefore, when studying or working with surface tension, always consider how temperature changes might affect it. This phenomenon is essential in various applications, from industrial processes to biological systems.

Cohesive forces

Cohesive forces are the intermolecular forces that hold molecules of the same substance together. These forces are responsible for many of the unique properties of liquids, such as surface tension. Cohesive forces arise from the attractive forces between molecules, including hydrogen bonds, van der Waals forces, and other types of molecular interactions.

When cohesive forces are strong, the molecules at the surface tend to stick together tightly, resulting in high surface tension. Conversely, if the cohesive forces are weak, surface tension will be low. The strength of cohesive forces depends on the nature of the liquid; different liquids have different molecular structures, affecting how the molecules interact. This is why certain liquids, like water, have a much higher surface tension than others, such as alcohol.

• Intermolecular forces impact how molecules stick together.
• Strong cohesive forces lead to higher surface tension.
• The molecular structure of a liquid defines its cohesive force strength.

Surfactants

Surfactants are substances that significantly reduce the surface tension of a liquid. They achieve this by disrupting the cohesive forces between the liquid's molecules. Surfactants contain molecules with two distinct parts: a hydrophilic (water-attracting) head and a hydrophobic (water-repelling) tail. When added to a liquid, surfactants position themselves at the interface, with the head in the water and the tail sticking out.

This arrangement breaks the molecular bonds at the liquid’s surface, reducing the overall surface tension. This property of surfactants is why they are crucial in cleaning products. By decreasing water's surface tension, they allow it to spread more effectively and penetrate dirt and grease, enhancing cleaning efficiency. It's important to note that soaps and detergents are common surfactants used in everyday life.

Liquid concentration

Liquid concentration refers to the amount of a substance dissolved in a certain volume of liquid. It has a direct impact on the surface tension of the liquid because it alters the density and arrangement of molecules at the surface. As the concentration of a solute in a liquid increases, the surface tension can also increase. This occurs because more molecules are present at the surface, strengthening the cohesive forces among them.

Concentration influences surface behavior, playing a fundamental role in various chemical processes and industrial applications. Understanding this concept is essential when working with solutions and mixtures, as the concentration can significantly alter the properties and functionality of a liquid. When dealing with concentrated solutions, expect changes in properties like viscosity and surface tension, which could affect their performance in practical uses.