Surprise Quiz - Surface Chemistry

The answer is gas-gas because gases are highly compressible and have no fixed volume or shape. Therefore, it is not possible to obtain an interface between two gases since they can easily mix and blend with each other.

The term "sorption" refers to the process of substances being either absorbed or adsorbed. Absorption occurs when one substance is taken in and incorporated into another substance, while adsorption refers to the attachment of molecules to the surface of a solid or liquid. Therefore, the correct answer is both absorption and adsorption.

At the equilibrium position in the process of adsorption, the change in enthalpy (∆H) is equal to the product of temperature (T) and the change in entropy (∆S). This is represented by the equation ∆H = T∆S. This means that the heat absorbed or released during the adsorption process is directly proportional to the temperature and the change in entropy.

When the temperature is increased, the kinetic energy of the gaseous species increases, allowing it to overcome the attractive forces of physical adsorption and leading to desorption. At higher temperatures, the gaseous species may undergo chemical reactions with the adsorbent, forming chemical bonds and transitioning from physical adsorption to chemical adsorption. Therefore, an increase in temperature can cause the change from physical adsorption to chemical adsorption.

Physisorption is the process by which gas molecules are attracted to and adhere to the surface of a solid. The extent of physisorption is influenced by various factors. A decrease in temperature causes a decrease in the kinetic energy of gas molecules, reducing their ability to overcome the attractive forces of the solid surface. As a result, the gas molecules are more likely to be adsorbed onto the surface, leading to an increase in the extent of physisorption. Therefore, the correct answer is decrease in temperature.

Adsorption is a process in which molecules or ions from a gas or liquid adhere to the surface of a solid. The enthalpy change (∆H) represents the heat energy absorbed or released during a reaction. In the context of adsorption, ∆H > 0 implies that the process is endothermic, meaning heat is absorbed from the surroundings. However, adsorption is typically an exothermic process, where heat is released. Therefore, ∆H > 0 is not applicable to the phenomenon of adsorption.

When a beam of light passes through a solution, it may scatter off the particles present in the solution, making the beam visible. This scattering of light by particles is known as the Tyndall effect. Aqueous solutions of soap above the critical micelle concentration contain micelles, which are clusters of soap molecules. These micelles act as particles and can scatter light, causing the Tyndall effect. In contrast, aqueous solutions of soap below the critical micelle concentration do not form micelles and therefore do not show the Tyndall effect. Aqueous solutions of sodium chloride and sugar do not contain particles large enough to scatter light, so they do not exhibit the Tyndall effect.

In physisorption, the adsorbent does not show specificity for any particular gas because the involved van der Waals forces are universal. Van der Waals forces are weak intermolecular forces that exist between all molecules, regardless of their chemical composition. These forces arise from temporary fluctuations in electron distribution, creating temporary dipoles that attract neighboring molecules. Since van der Waals forces are present between all gas molecules, the adsorbent does not discriminate between different gases and can adsorb any gas that comes into contact with it.

The extent of adsorption of adsorbate from the solution phase increases with an increase in the amount of adsorbate in the solution. This is because a higher concentration of adsorbate provides more opportunities for the adsorbate molecules to come into contact with the adsorbent surface and form stronger interactions. As a result, more adsorbate molecules are adsorbed onto the surface, leading to an increase in the extent of adsorption.

High temperature is not a favorable condition for physical adsorption because it leads to an increase in the kinetic energy of the adsorbate molecules. This increased energy causes the adsorbate molecules to move more rapidly, making it difficult for them to be attracted and held onto the surface of the adsorbent. As a result, physical adsorption is less likely to occur at high temperatures.

A colloidal system with a solid substance as a dispersed phase and a liquid as a dispersion medium is classified as a sol. In a sol, the solid particles are dispersed evenly throughout the liquid, forming a stable suspension. This is different from a solid sol, where the solid substance is dispersed in another solid medium, a gel, where the dispersion medium is a solid, and an emulsion, where the dispersed phase is a liquid and the dispersion medium is another immiscible liquid.

Water on calcium chloride is an example of absorption because calcium chloride has a strong affinity for water molecules. When water comes into contact with calcium chloride, the water molecules are attracted to the chloride ions in the calcium chloride, leading to the water being absorbed or taken up by the calcium chloride. This process is known as absorption, where one substance is taken up or soaked into another substance.

Freshly prepared precipitate sometimes gets converted to colloidal solution by peptisation. Peptisation is a process in which a precipitate is broken down into smaller particles and dispersed in a solvent, forming a colloidal solution. This is achieved by adding a suitable dispersing agent or by vigorous stirring or shaking. Peptisation helps in stabilizing the colloidal solution and preventing the particles from re-aggregating or settling down.

At high concentration of soap in water, soap molecules form aggregates or clusters called micelles. These micelles are formed due to the hydrophobic tails of the soap molecules being attracted to each other and forming a core, while the hydrophilic heads remain on the outer surface. This behavior is characteristic of associated colloids, where the particles are formed by the association of smaller particles or molecules. Therefore, at high concentrations, soap behaves as an associated colloid.

Lyophobic sols are formed by substances that are not easily dispersed or dissolved in a solvent. They tend to aggregate and form clumps. Adding a lyophilic sol, which is a solute that has an affinity for the solvent, can help stabilize the lyophobic sol. The lyophilic sol particles surround the lyophobic sol particles, preventing them from aggregating and improving their stability. Therefore, adding a lyophilic sol is a method of protecting a lyophobic sol.

Na3PO4 will have the maximum coagulating value for AgI/Ag+ sol because it contains three sodium ions and one phosphate ion. The phosphate ion can form strong bonds with the silver ions, causing the formation of a solid precipitate. This precipitate will effectively coagulate the AgI/Ag+ sol, leading to maximum coagulating value.

The correct answer is (b), (c) because it includes options (b) and (c) which are the preferred choices.

Homogeneous catalysis is the process in which the catalyst and reactants are in the same phase. In this process, the catalyst is uniformly distributed throughout the reaction mixture. Therefore, there is no interface of phases involved in homogeneous catalysis. On the other hand, crystallization occurs at the interface of the liquid and solid phases, heterogeneous catalysis occurs at the interface of different phases (solid-gas or solid-liquid), and corrosion occurs at the interface of a metal and its surrounding environment.

Colloidal particles are comparatively less in number compared to the particles in true solutions of the same concentration. This is why the values of colligative properties, such as boiling point elevation or freezing point depression, are of a small order in colloidal solutions. The small number of colloidal particles results in a lower concentration of solute particles, which leads to a smaller effect on the colligative properties.

The Freundlich adsorption isotherm describes a heterogeneous adsorption process where the adsorption capacity of the adsorbent increases with increasing concentration of the adsorbate. This is represented by a curve that starts steep and gradually levels off. Option 3 is the most suitable choice as it shows this characteristic behavior.

Coagulation is the process responsible for the formation of a delta at a place where rivers meet the sea. Coagulation refers to the clumping together of particles in a liquid to form larger, heavier particles. In the case of a delta, as the river flows into the sea, the sediment it carries undergoes coagulation, causing the particles to settle and accumulate, eventually forming a landform known as a delta. This process is essential in the formation and growth of deltas around the world.

The correct answer is "a → b → c → d → e" because it follows a logical sequence where each element is connected to the next element in a consistent pattern. Starting with "a", it leads to "b", which leads to "c", and so on until it reaches "e". This sequence maintains a clear and logical progression, making it the most appropriate choice.