Question

Mark the statement which is correct: (a) Surface tension of a liquid increases with temperature. (b) Addition of chemicals reduces the surface tension of a liquid. (c) Stalgmometer is used for measuring viscosity of the liquid. (d) Viscosity of a liquid does not depend on intermolecular forces.

Short answer

The correct statement is (b) Addition of chemicals reduces the surface tension of a liquid.

Step-by-step solution

Analyse option (a)

Surface tension of a liquid is the result of cohesive forces between liquid molecules. However, as the temperature increases, these cohesive forces become weaker, and thus, the surface tension decreases. Therefore, statement (a) is incorrect.

Analyse option (b)

The addition of chemicals such as detergents or other surfactants can indeed reduce the surface tension of a liquid. This is because these chemicals disrupt the cohesive forces between the liquid molecules, reducing the surface tension. Therefore, statement (b) is correct.

Analyse option (c)

A stalgmometer is not used for measuring viscosity of a liquid. It's a device used to measure surface tension. Hence, statement (c) is incorrect.

Analyse option (d)

Viscosity of a liquid is directly related to the intermolecular forces in the liquid. Stronger forces result in higher viscosity and vice versa. Consequently, statement (d) is incorrect.

Key concepts

Temperature Effects on Surface Tension

Understanding the relationship between temperature and surface tension is crucial in many applications ranging from industrial processes to daily life instances like cleaning. Imagine a skipping stone gliding across a pond; the stone is supported in part by the water's surface tension, which decreases as the mercury rises.

As temperature increases, the kinetic energy of molecules in a liquid escalates, leading them to move more vigorously and break away from their neatly ordered arrangement at the surface. This causes a weakening in the cohesive forces that bind the molecules together, thus decreasing surface tension. Think of it as a tightly knit sweater that loosens up as it warms, allowing more space between the stitches. Therefore, when we increase the temperature, the surface of a liquid becomes less capable of acting like a stretched elastic membrane.

In practical terms, heating a liquid can make it easier to spread over a surface, which is beneficial in processes such as painting or cleaning. Keeping this concept in mind could be a helpful tip when dealing with tasks that involve liquid spreading or penetration.

Surfactants

The term 'surfactant' might sound complex, but you encounter these substances daily. Surfactants, or surface active agents, are like skilled negotiators, bridging the gap between water and oils or dirt, allowing them to mix and be washed away easily.

By their nature, surfactants possess a double-ended molecular structure; one end is hydrophilic (water-loving) and the other is hydrophobic (water-repelling). When added to a liquid, surfactants head straight to the surface, where they wedge themselves between the liquid molecules, breaking up the tight pack and reducing surface tension.

Game Changers in Cleaning

Without surfactants, soaps wouldn't 'soapy' at all — they significantly improve the cleaning power by allowing water to mix with oil and dirt, making it easier to remove these unwanted substances from our clothes, dishes, or even our hands. In a broader context, surfactants' ability to reduce surface tension is utilized in various industries, from oil recovery to fabric production, showcasing their versatility.

Viscosity of Liquids

Viscosity can be thought of as a liquid's internal friction, a measure of its resistance to flow. Imagine pouring syrup onto your pancakes. It flows slowly because its high viscosity, unlike water, which pours quickly due to its low viscosity.

Liquids with higher viscosity move sluggishly because their molecular structure allows for strong intermolecular forces, which need considerable energy to overcome. On the flip side, liquids with low viscosity have weaker intermolecular forces and thus, flow more freely.

The Role of Temperature

Just like how the temperature influences surface tension, it also affects viscosity. Heating a viscous fluid tends to lower its viscosity — similar to warming up that syrup, making it pour more easily. However, it's not just temperature that plays a role; the type of molecules and the strength of attraction between them are what fundamentally determine a liquid's viscosity.

In industrial applications, understanding liquid viscosity is crucial for processes like pumping, mixing, and transporting liquids. Engineers take great care to ensure that liquids are at the correct temperature to maintain the desired flow characteristics for these processes.