Colloids and Surfaces MCQ Quiz in मल्याळम - Objective Question with Answer for Colloids and Surfaces - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

The correct answer is 

Explanation:-

In case of diatomic molecule,

comparing it with straight line equation, 

y = mx + c 

Conclusion:-

So,  the slope of is 

The correct answer is (I) and (III)

Concept:-

Surfactant Types and Their Interactions
Anionic surfactants contain negatively charged head groups. They are commonly used in detergents and shampoos. The electrostatic repulsion between the heads makes it harder for them to pack tightly and form micelles, requiring a higher surfactant concentration to reach the CMC.

Non-ionic surfactants don't carry a charge on their head groups. This absence of charge reduces electrostatic repulsion, facilitating micelle formation at a lower concentration than ionic surfactants of the same chain length.

Micelle Formation Process
The process of micelle formation is entropically driven and involves a balance between hydrophobic interactions (leading surfactant tails to avoid water) and hydrophilic interactions (interaction of the head groups with water). At concentrations below the CMC, surfactant molecules are primarily dispersed individually. Upon reaching the CMC, the thermodynamic favorability of reducing the hydrophobic tails' water exposure leads to the spontaneous formation of micelles.

Explanation:-

(I) Higher CMC of anionic vs. non-ionic surfactants: Due to electrostatic repulsion among anionic head groups, more surfactant molecules are needed to overcome this barrier and form micelles, resulting in a higher CMC for anionic surfactants compared to non-ionic ones.

(III) Decrease of CMC with added electrolytes: The introduction of ions screen the repulsive forces among ionic surfactant molecules, facilitating micelle formation at a lower surfactant concentration, hence decreasing the CMC.

 Additional Information

(II) This option is incorrect because the presence of electrostatic repulsion in anionic surfactants increases, not decreases, the CMC when compared to non-ionic surfactants, as mentioned above.

(IV) This statement contradicts the shielding effect provided by electrolytes, which, by reducing electrostatic repulsion, lowers the CMC of ionic surfactants rather than increasing it. Thus, option (IV) is incorrect.

Conclusion:-

So, the correct statements are (I) and (III).

The Correct Answer is flocculation and coagulation.

Concept:-

Flocculation:

• In a colloidal suspension, the particles are finely dispersed and remain suspended due to electrostatic repulsion between them. This repulsion prevents the particles from aggregating and settling out of the solution. Flocculation is the process of overcoming this repulsion and allowing the particles to come closer together, forming larger aggregates or flocs.
• Flocculants are added to neutralize the charges on the particles, allowing them to aggregate and settle.

Coagulation:

• ​Colloidal particles in a suspension are stabilized by electrostatic repulsion, preventing them from aggregating and settling. Coagulation is the process of destabilizing these colloidal particles by neutralizing the repulsive forces, allowing them to come together and form larger, settleable particles.
• Coagulants are added to the suspension to neutralize charges, reduce repulsion, and promote particle collision and aggregation.

Flocculation and Coagulation are used in water and wastewater treatment, mining, papermaking, and other industries where separation of suspended particles is necessary.

Explanation:-

When river water containing colloidal clay flows into the sea, charged molecules of the colloidal particles of river water get neutralized by the salt present in salt water resulting in the silt. This phenomenon is called flocculation and coagulation.

Conclusion:-

When river water containing colloidal clay flows into the sea, the major cause of silting is flocculation and coagulation.

Concept:-

• Adsorption: Adsorption is a surface process where molecules or atoms (adsorbate) accumulate on the surface of a material (adsorbent). The process can be described via rate equations, where ka (adsorption rate constant) and kb (desorption rate constant) feature prominently for the proportion of molecules bound to the surface at a given time versus those released back into the gaseous phase.
• Langmuir Isotherm Model: The key concept in the Langmuir adsorption isotherm model is that the surface of the adsorbent is uniform and each site on the surface is equivalent, i.e., each site has an equal chance of adsorbing a molecule.
  The model is formulated as:

         θ = kaP / (1 + kaP)

Explanation:-

The correct relation between K and P at a fixed temperature is :

From above equation 

Conclusion:-

So, For a fixed fractional coverage, the correct relation between K and P at a fixed temperature is 

The correct answer ø = Kp/(1+Kp)

Concept:-

Adsorption isotherms: it illustrate the connection between the degree of adsorption (denoted as θ) and the concentration or pressure of the adsorbate (denoted as p) at a specific temperature. The Langmuir isotherm model is commonly applied to represent this relationship, especially when describing the adsorption of a monolayer of molecules on a surface.

Equilibrium Constant (Kp): The equilibrium constant (Kp) in the Langmuir isotherm equation reveals the balance between the rate of adsorption and the rate of desorption. Kp relies on factors such as the adsorption energy and the number of available sites on the surface. A higher Kp indicates a more significant adsorption tendency.

Fractional Surface Coverage (θ): The symbol θ represents the fractional surface coverage, signifying the proportion of available adsorption sites that are occupied by adsorbate molecules. It ranges from 0 (indicating no adsorption) to 1 (indicating complete coverage by a monolayer). The Langmuir isotherm equation predicts how θ changes with variations in p.

Explanation:-

The Langmuir isotherm is a fundamental model used to describe the adsorption of molecules onto a surface, such as in the case of gas adsorption on a solid surface. The correct form of the Langmuir isotherm equation is as follows:

ø = Kp/(1+Kp)

θ represents the fractional surface coverage or the fraction of sites occupied by adsorbed molecules.
Kp is the equilibrium constant, which is related to the adsorption energy and the number of available sites.
p is the pressure of the gas or the concentration of the adsorbate in the gas phase.

Concept:-

• Surface tension is the force exerted per unit length on the surface of a liquid due to the cohesive nature of its molecules. It is the tendency of the surface of a liquid to minimize its surface area and form a shape that has the minimum surface area possible.

• The SI unit of surface tension is Newtons per meter (N/m) or Joules per square meter (J/m²).

Explanation:-

• The surface tension of a liquid is influenced by the intermolecular forces between its molecules, which determine the cohesive forces that hold the molecules together. A decrease in surface tension indicates a decrease in the strength of the cohesive forces between the molecules, while an increase in surface tension indicates an increase in the strength of the cohesive forces.
• Given that the surface tension of the solution of A is smaller than that of pure water, it implies that the intermolecular forces between the molecules of A are weaker than those of water. This can occur if A is a surfactant or a solute that disrupts the hydrogen bonding network of water molecules at the surface.
• On the other hand, the fact that the surface tension of the solution of B is greater than that of pure water suggests that the intermolecular forces between the molecules of B are stronger than those of water. This can occur if B is a polar compound that can form hydrogen bonds with water molecules or if B has a larger molecular size that contributes to stronger van der Waals forces between the molecules.
• Therefore, one can infer that the surface concentration of A is larger than that of B, since the weaker intermolecular forces of A compared to water would require a higher concentration of A at the surface to compensate for the loss of cohesive forces. Hence, the correct option is (3) - the surface concentration of A is larger than that of B.

Explanation:-

• Correct option is (3). 

Concept:

→ The order of a surface catalyzed unimolecular reaction can depend on the pressure of the reactant. At very low pressures of the reactant, the reaction is typically first-order, while at very high pressures, the reaction is typically zero-order.

→ This is because the rate of a surface catalyzed reaction depends on the concentration of the reactant molecules adsorbed onto the surface of the catalyst.

→ At very low pressures of the reactant, there are few reactant molecules adsorbed onto the catalyst surface, and the rate of the reaction is limited by the rate at which reactant molecules adsorb onto the surface.

→ In this case, the rate of the reaction is proportional to the concentration of the reactant, and the reaction is first-order.

→ At very high pressures of the reactant, the catalyst surface becomes saturated with reactant molecules, and the rate of the reaction becomes limited by the rate at which the reactant molecules react with each other on the catalyst surface.

→ In this case, the rate of the reaction is independent of the concentration of the reactant, and the reaction is zero-order.

Conclusion: Therefore, the order of a surface catalyzed unimolecular reaction, at very low and very high pressures of the reactant, would be 1 and 0, respectively.

Concept:

The height to which a liquid rises in a capillary tube can be calculated using the following equation:

,

where:

• h is the height to which the liquid rises
• T is the surface tension of the liquid
• θ is the angle of contact between the liquid and the capillary tube
• ρ is the density of the liquid
• g is the acceleration due to gravity
• r is the radius of the capillary tube.

Explanation:

We can rearrange this equation to solve for the surface tension:

Substituting the given values, we get:

Note that the angle of contact between the liquid and the capillary tube is assumed to be 0° because the liquid wets the capillary completely.

Converting the units to Nm⁻¹, we get:

T ≈ 0.054 Nm⁻¹.

Conclusion:
Therefore, the surface tension of the liquid is closest to 0.05 Nm⁻¹.

Concept:

Capillary Rise:

Suppose a liquid has surface tension  with density  rises to height h in a capillary whose inner radius is r and g is the acceleration due to gravity, then the formula  which is generally employed to find the rise in the capillary is:

• Surface tension, cohesion, and adhesion forces cause the liquid to rise.
• The liquid will rise, similar to how water does in a glass capillary if the adhesive force between the liquid and the capillary is greater than the cohesive force between the liquids. In this instance, the meniscus is concave, and the contact angle is less than 90 degrees.
• As in the instance of mercury in a glass capillary, liquid depresses if the cohesive force is greater than the adhesive force. In this instance, the meniscus is convex, and the contact angle is more than 90 degrees.

Explanation:

Given Data:

Let  and  be the surface tension of liquid A and liquid B.

And  and  be the density of liquid A and liquid B.

The surface tension of liquid A, 

The density of liquid A, 

Height of liquid A = 10 cm

  and  be the contact angles that are the same for both liquids A and B.

The formula used to calculate the rise in capillary B is:

For capillary A:

 ........ (1)

For capillary B:

 .......... (2)

Divide equation (1) by (2)

 ......... (3)

Now, substitute all the given values in (3)

Conclusion:

Thus, if A rises 10 cm in a capillary then the rise (in cm) of liquid B in the same capillary at the same temperature will be equal to 40 cm.

Concept:

The surface area occupied = Total number of molecules combining for complete monolayer coverage × Area of 1 molecule

At STP,

1 mole gas = 22.4 L

22.4 L = 6.022 × 10²³ molecules

22.4 L = N_A

No. of molecules in 1 L = 

No. of molecules in V_m = 

where V_m = volume corresponding to total a complete monolayer coverage.

Explanation:

∵ The volume of N₂ at STP required to form a monolayer on a porous solid surface is = 22.4 cm³ g^-1

→ Area occupied by one molecule of nitrogen gas molecule = 16.2 Å²

= 16.2 × 10^-16 cm²

we know that (1 L = 10³ cm³)

∴ 22400 cm³ of N₂ at STP contains N_A molecules of N₂

∴ 22.4 cm³g^-1 of N₂ contains

= 

= 6.022 × 10²⁰ molecules of N₂

∴ Surface area occupied by 6.022 × 10²⁰ molecules of N₂,

= 6.022 × 10²⁰ × 16.2 × 10^-16 cm²

= 97.55 × 10⁴

= 9.755 × 10⁵ cm² g^-1

Conclusion:-
So, the option '2' is correct.