Question

The viscosity of which liquid is highest? (a) Water (b) Glycol (c) Acetone (d) Ethanol

Short answer

The liquid with the highest viscosity is (b) Glycol.

Step-by-step solution

Understanding Key Concepts

Before making comparisons, it is important to understand that viscosity is a fluid's resistance to flow. In other words, viscous liquids are 'thicker' or 'stickier' and flow slower than less viscous liquids.

Comparing Liquid Viscosities

Indeed, without a specific temperature, the viscosity of liquids can vary. However, under typical conditions, glycol has a higher viscosity compared to water, acetone, and ethanol. So, (b) Glycol has the highest viscosity.

Key concepts

Fluid Dynamics

Fluid dynamics explores how fluids behave when they are in motion. It is a sub-discipline of fluid mechanics. At its core, fluid dynamics investigates the flow behaviors of liquids and gases. Key considerations in this field include:

• Viscosity: This is critical in determining how a fluid flows. Thick fluids with high viscosity, like honey, flow slower than those with low viscosity, like water.


• Flow types: Fluids may experience laminar (smooth) or turbulent (chaotic) flow depending on their speed and other factors.
• Reynolds number: This dimensionless value helps predict flow patterns based on fluid velocity and characteristic length.

By understanding how these attributes interact, fluid dynamicists can solve real-world problems, from predicting weather patterns to optimizing fuel efficiency in vehicles. The concept of viscosity is especially pertinent as it affects the resistance experienced by objects as they move through a fluid.
It acts almost like an internal friction within the fluid, resisting deformation when stress is applied.

Physical Chemistry

Physical chemistry focuses on understanding the macroscopic, atomic, and subatomic phenomena in chemical systems through the lens of physical principles. Viscosity, a significant property of liquids, isn't just about flow but is an essential aspect of understanding molecular interactions.

• Molecular structure: The shape and size of molecules influence how they move past each other, affecting viscosity. For example, glycerol has a higher viscosity due to its larger and more complex molecular structure compared to water.


• Intermolecular forces: Liquids with strong intermolecular forces, such as hydrogen bonds or van der Waals forces, generally exhibit higher viscosities.


• Temperature effects: As temperature increases, molecules move faster and overcome intermolecular forces more easily, often reducing viscosity.

In summary, physical chemistry helps us predict how changes in molecular composition or environmental conditions impact the viscosity of a fluid, thereby influencing fluid dynamics and the broader study of liquid properties.

Liquid Properties

Liquids possess unique properties that distinguish them from other states of matter, such as solids and gases. Understanding these properties enables us to predict and explain various phenomena. One of the fundamental properties of a liquid is viscosity, which defines how it resists flow. Here are a few important liquid properties:

• Density: This measures how much mass a liquid has in a given volume. It influences buoyancy and how liquids mix with each other.


• Surface Tension: Resulting from cohesive forces between molecules, it allows objects to float or sink and dictates the shape of liquid droplets.
• Boiling and melting points: These are the temperatures at which a liquid turns to gas or solidifies, respectively.

Exploring these properties offers insights into how liquids behave under different conditions and contexts. For example, glycol's high density and surface tension relate to its viscosity, explaining why it flows more sluggishly than water or ethanol. Appreciating these properties helps us harness liquids for various applications, from industrial to everyday use.