Question

The molecular viscosity of a liquid is given by (a) viscosity \(\times\) mol. wt. (b) viscosity \(\times\) molar volume (c) viscosity \(\times\) molar surface (d) none

Short answer

The correct answer is (b):viscosity \(\times\) molar volume.

Step-by-step solution

Understand the concept of viscosity

Firstly, note that viscosity refers to a liquid's resistance to flow. When it comes to molecular viscosity, it is influenced by several factors, such as the size and shape of the molecules, as well as the strength of the intermolecular forces.

Review the options

Option (a) suggests that the molecular viscosity is calculated by the product of viscosity and molecular weight. This is incorrect as the molecular weight does not have a direct link to the viscosity of a liquid.

Evaluate remaining options

Option (b) suggests that the molecular viscosity is calculated by the product of viscosity and molar volume. This is the most accurate among the answer choices, as the volume occupied by one mole of a substance (molar volume) can impact the viscosity by affecting molecular interactions. Option (c) proposing the product of viscosity and molar surface is incorrect, since molar surface is not a standard term. Option (d) is not the correct answer because there is a relationship and it's shown in option (b).

Choose the correct answer

Based on the analysis of each option, the correct answer would be (b): viscosity \(\times\) molar volume because molar volume can affect the viscosity of the liquid by influencing molecular interactions.

Key concepts

Molecular Weight

Molecular weight, also known as molecular mass, is the sum of the atomic weights of all atoms in a given molecule. It's typically expressed in atomic mass units (amu) or Daltons (Da). This measure is significant because it helps determine the mass of one molecule of a substance, allowing us to calculate molar masses and perform stoichiometric calculations. However, it's important to note that molecular weight does not directly influence a liquid's viscosity. Instead, it's more relevant when considering the masses of substances in reactions or when calculating molar quantities for chemical solutions and compounds. Despite not being directly linked to viscosity, molecular weight can have an indirect influence by affecting the shape, size, and overall energy of molecular interactions, which could, in turn, impact flow resistance.

Molar Volume

Molar volume is defined as the volume occupied by one mole of a substance, usually expressed in units like liters per mole (L/mol). It is derived by dividing the molar mass by the density of the substance under specific conditions. The molar volume is crucial because it can impact how molecules move and interact with each other within a liquid.

• Higher molar volumes generally indicate less dense substances, allowing molecules more freedom to move around.
• This increased freedom can lead to less resistance to flow, influencing the viscosity.

Thus, the relation between viscosity and molar volume is significant, making molar volume a more accurate consideration for molecular viscosity than molecular weight. The volume occupied by molecules affects their packing and how they slide over each other, contributing to the liquid's resistance to flow.

Molecular Interactions

Molecular interactions are the various forces that act between molecules, influencing how they behave and interact with each other. These interactions include things like hydrogen bonding, van der Waals forces, and ionic or covalent bonds, each playing a role in the chemical properties and behaviors of substances.

• Strong interactions, like hydrogen bonds, can lead to high viscosity because they create a more cohesive structure, making it harder for the molecules to move past one another.
• On the other hand, weak interactions, like dispersion forces, may result in lower viscosity as molecules don't hold together as tightly, allowing easier flow.

Understanding molecular interactions is essential for predicting and explaining why certain liquids resist flow more than others. These interactions dictate how closely molecules are packed and how they influence the viscosity of the substance.

Intermolecular Forces

Intermolecular forces are types of attractive forces between molecules which play a crucial role in determining the physical properties of liquids. These forces include hydrogen bonding, dipole-dipole attractions, and London dispersion forces.

• Hydrogen bonding, observed in substances like water, significantly increases viscosity due to the strong attractions between molecules.
• Dipole-dipole interactions occur in polar molecules where positive and negative charges attract, also contributing to higher viscosity.
• London dispersion forces, present in all molecules, are the weakest of these forces but become more significant in larger molecules, potentially affecting viscosity.

The intensity of intermolecular forces has a direct correlation with viscosity: stronger forces result in higher viscosity because they restrict the movement of molecules within the liquid. Thus, comprehending these interactions allows us to better understand how different substances flow and behave under various conditions.