Surface Chemistry

Step 1: Concept
Pesticide spray is an aerosol.
Step 2: Analysis
In a spray, liquid droplets are dispersed in a gaseous medium.
Step 3: Conclusion
Dispersing phase is liquid and dispersion medium is gas.
Final Answer: (D)

Step 1: Concept
Flocculation value is inversely proportional to coagulating power.
Step 2: Analysis
is a positively charged sol. According to Hardy-Schulze rule, the ion with the lowest negative charge ( in ) has the lowest coagulating power.
Step 3: Conclusion
Lower coagulating power results in the maximum flocculation value.
Final Answer: (A)

Step 1: Concept
Flocculation value is inversely proportional to coagulating power.
Step 2: Analysis
is a positively charged sol. According to Hardy-Schulze rule, the ion with the lowest negative charge ( in ) has the lowest coagulating power.
Step 3: Conclusion
Lower coagulating power results in the maximum flocculation value.
Final Answer: (A)

Step 1: Identifying Curves
Curve OA: Pressure is constant (Isobaric). Curve OD: Volume is constant (Isochoric).
Step 2: Slope Comparison
Both Isothermal (OB) and Adiabatic (OC) curves are curves, but the adiabatic slope is steeper.
Step 3: Conclusion
Since OC is steeper than OB, it represents the Adiabatic process.
Final Answer: (d)

Step 1: Concept
Resonance occurs when inductive reactance ( ) equals capacitive reactance ( ).
Step 2: Analysis
At resonance, the net reactance is zero, making the circuit purely resistive.
Step 3: Conclusion
In a purely resistive circuit, current and voltage are in phase, so the phase difference is zero.
Final Answer: (C)

Step 1: Mechanism
A voltmeter always draws some current from the cell during measurement, which leads to a potential drop across the internal resistance.
Step 2: Null Method
A potentiometer works on the "null deflection" method, meaning it draws no current from the cell when balanced.
Step 3: Conclusion
Because no current is drawn, the potentiometer measures the true electromotive force (emf) accurately.
Final Answer: (d)

Step 1: Understanding multimolecular colloids.
Multimolecular colloids consist of aggregates of molecules that are small enough to remain in suspension, and their size is typically between 1 nm and 1000 nm.

Step 2: Explanation of the options.
- (1) Soap solution: Soap solutions contain micelles, which are not multimolecular colloids.
- (2) Sol of proteins: Proteins are macromolecules and generally form macromolecular colloids, not multimolecular.
- (3) Sol of gold: Gold nanoparticles in sol are an example of multimolecular colloids, where gold atoms aggregate.
- (4) All of these: This is incorrect because soap solutions and sol of proteins are not multimolecular colloids.

Step 3: Conclusion.
The correct answer is (3) Sol of gold.

Step 1: Identifying the types of forces in adsorption.
In physical adsorption, the gas molecules are held by weak forces, mainly van der waals' forces, which are temporary dipole interactions between molecules.

Step 2: Explanation of the options.
- (1) Strong chemical forces: Chemical forces are involved in chemisorption, not in physical adsorption.
- (2) Van der waals’ forces: This is the correct option. In physical adsorption, van der waals’ forces are responsible for holding the gas molecules to the surface.
- (3) Metallic bonds: Metallic bonds are not involved in adsorption.
- (4) Gravitational forces: Gravitational forces are too weak to play a significant role in adsorption.

Step 3: Conclusion.
The correct answer is (2) Van der waals’ forces.

Step 1: Formula / Definition}

Step 2: Calculation / Simplification}
From Latimer diagram:
(4e, 1e)
(5e)


(with given data)
Step 3: Final Answer

Step 1: Formula / Definition}

Step 2: Calculation / Simplification}


is more easily oxidized (lower reduction potential).
Spontaneous: (anode)
(cathode)
Overall:
Step 3: Final Answer

Concept: Types of adsorption.

Step 1: Physical adsorption involves weak intermolecular forces.

Step 2: These are van der Waals’ forces.

Step 3: Chemical adsorption involves strong covalent/ionic bonds.
Conclusion:
Physical adsorption uses van der Waals’ forces.

Step 1: Understanding the Concept:
Adsorption is an exothermic process that results in a decrease in entropy.

Step 2: Detailed Explanation:
Adsorption is spontaneous at low temperatures. It is an exothermic process because energy is released when gas molecules bind to the surface ( ). Additionally, when gas molecules become confined to a surface, their freedom of movement decreases, leading to a decrease in entropy ( ).

Step 3: Final Answer:
During adsorption, and , which corresponds to option (C).

Step 1: Understanding the Concept:
Colloidal solutions are classified based on the dispersed phase and the dispersion medium.
Step 2: Detailed Explanation:
\begin{itemize} \item Fog: Tiny liquid water droplets dispersed in air (gas). So, dispersed phase is liquid, dispersion medium is gas. \item Smoke: Solid in gas. \item Foam: Gas in liquid. \item Cloud: Liquid in gas. \end{itemize}
Step 3: Final Answer:
Fog is a colloidal solution of liquid in gas, option (C).

Step 1: Understanding the Concept:
In the blast furnace extraction of iron, slag is formed by the reaction of flux (limestone) with impurities (silica).
Step 2: Detailed Explanation:
The slag formed is calcium silicate ( ). It has a lower density than molten iron, so it floats on top of the molten iron, allowing easy separation. It also has a lower melting point than iron, ensuring it remains molten and can be tapped off separately.
Step 3: Final Answer:
The correct statement is that the slag is lighter and has a lower melting point than the metal, option (A).

Step 1: Understanding the Concept:
The average kinetic energy for a gas is given by , where n is the number of moles. This is the total translational kinetic energy.
Step 2: Detailed Explanation:
Given: mass of = 1 g, Molar mass of = 32 g/mol. Number of moles, mol. Temperature, K. . Total kinetic energy = = = J ≈ J.
Step 3: Final Answer:
The kinetic energy is J, option (C).

Step 1: Understanding the Concept:
CsCl has a body-centered cubic (BCC) structure. In the CsCl structure, the Cl ions form a simple cubic lattice, and the Cs ion occupies the body center. The ions touch along the body diagonal.
Step 2: Detailed Explanation:
In the CsCl structure, the relationship between the edge length (a) and the sum of the ionic radii (r + r ) is given by: Given: Å, Å. Sum of radii = Å. Thus, Å. So, Å.
Step 3: Final Answer:
The edge length of the unit cell is 4.04 Å, option (A).

Step 1: Understanding the Concept:
Lyophilic sols are solvent-loving.
Step 2: Detailed Explanation:
Lyophilic sols are stable due to strong solvation (interaction between dispersed phase and dispersion medium).
Step 3: Final Answer:
Lyophilic sols are stable because the colloidal particles are solvated.

Step 1: Understanding the Concept:
ZnS has zinc blende structure.
Step 2: Detailed Explanation:
In ZnS (zinc blende structure), each Zn is surrounded by 4 S ions. Coordination number is 4.
Step 3: Final Answer:
Coordination number is 4.

Step 1: Understanding the Concept:
Equivalent mass = .
Step 2: Detailed Explanation:
At STP, L of mol . Mass of g. Equivalent mass of metal = g.
Step 3: Final Answer:
The mass of the element is g.

Step 1: Understanding the Concept:
Compressibility factor measures deviation from ideal gas behaviour.
Step 2: Detailed Explanation:
; for ideal gas, .
Step 3: Final Answer:
.