Surface Chemistry MCQ Quiz - Objective Question with Answer for Surface Chemistry - Download Free PDF

CONCEPT:

Adsorption of Gas on Solid Surface

• Adsorption is a surface phenomenon where molecules of a gas adhere to the surface of a solid.
• The extent of adsorption depends on factors such as the nature of the gas, nature of the adsorbent, temperature, and pressure.
• Gases with a higher critical temperature are adsorbed more easily because they are more polarizable and have stronger intermolecular forces, which enhance adsorption.
• Gases that are easily liquefiable (having high critical temperatures) are generally adsorbed more efficiently on solid surfaces.

Explanation:-

• Given that adsorption is less when:
  • The critical temperature of the gas is low because lower critical temperatures indicate weaker intermolecular forces and less polarizability, making adsorption less favorable.
  • Gases that are not easily liquefiable (indicating low critical temperatures) are less likely to be adsorbed efficiently.

The correct answer is 2) the critical temperature of the gas is low

CONCEPT:

Chemisorption

• Chemisorption, or chemical adsorption, involves the formation of a chemical bond between the adsorbate and the surface of the adsorbent.
• This type of adsorption is typically highly specific to the adsorbate and adsorbent involved.
• Chemisorption usually has a high enthalpy of adsorption due to the chemical bond formation.
• It is generally irreversible because the process involves breaking and forming of chemical bonds.

EXPLANATION:

• We know that chemisorption involves specific interactions between the adsorbate and the surface, which means it is highly specific.
• It also has a high enthalpy of adsorption due to the formation of strong chemical bonds.
• Additionally, chemisorption is generally irreversible because breaking these bonds requires significant energy.
• Therefore, the statement "Lack of specificity" does not describe chemisorption.

Therefore, the correct answer is Lack of specificity.

CONCEPT:

Adsorption Principle in Purification Methods

• Adsorption is a process in which atoms, ions, or molecules from a substance (which can be a gas, liquid, or dissolved solid) adhere to a surface of the adsorbent.
• It is widely used in various purification methods to separate components based on their different affinities to the adsorbent material.

EXPLANATION:

• In the context of the given purification methods:
  • Chromatography: This technique relies on adsorption principles, where different compounds in a mixture adhere to the stationary phase (adsorbent) to varying degrees, allowing their separation.
  • Sublimation: This process involves changing a substance from solid to gas without passing through the liquid phase and is not related to adsorption.
  • Extraction: This method involves separating components based on their solubilities in different immiscible liquids and does not involve adsorption.
  • Distillation: This technique separates substances based on their different boiling points and does not utilize adsorption.

Therefore, the correct answer is option 1: Chromatography, which uses the adsorption principle for purification.

A sol is a colloidal suspension of very small solid particles in a continuous liquid medium. Sol particles typically have a charge that can be positive or negative, depending on the type of sol and the conditions of its preparation.

Among the options you provided:

• Starch - Typically, starch sols are negatively charged.
• Gum - Gum-based sols are generally not characterized by a specific charge without more context, but they are usually not particularly known for carrying a positive charge.
• Gold Sol - Gold sols are negatively charged. However, without specifying the stabilizing agent or the preparation method, we cannot definitively say it's positively charged. Historically, negatively charged gold sols are more commonly mentioned in literature due to the stabilizing agents commonly used.
• Blood is a positively charged colloid whereas sols of starch, gum & gold are negatively charged. 

Explanation:

Enthalpy of adsorption is high - is NOT a characteristic of physisorption.

• Adsorption - The accumulation of molecular species at the surface rather than in the bulk of a solid or liquid.
• Two types of adsorption of gases on solids - Physisorption (physical adsorption) and Chemisorption (chemical adsorption).
• Physisorption (physical adsorption) - When the accumulation of gas on the surface of a solid occurs on account of weak van der Waals' forces.
• Chemisorption (chemical adsorption) - When the gas molecules or atoms are held to the solid surface by chemical bonds.

In physisorption, enthalpy of adsorption is low ( 20- 40 kJ mol^–1 ) whereas in the case of chemisorption enthalpy of adsorption is high (80 – 240 kJmol^–1 ) 

A colloid is a mixture in which one substance of microscopically dispersed insoluble particles are suspended throughout another substance.

• Dispersed phase: The phase that is scattered or present in the form of colloidal particles is known as dispersed phase.
• Dispersion medium: The medium in which the colloidal particles are dispersed is called dispersion medium.

Classification of colloids:

Hence we can conclude that 'Clouds' are examples of Aerosol.

The correct answer is Coagulation.

Key Points

• Alum helps in purifying water by coagulating the mud particles.
• The mud particles thus formed a gelatin-like precipitate, sp the particle size increases.
• Hence, the heavy particles settle down as precipitates and water becomes purified.

Additional Information

• In absorption, the substance you add to the water would fully absorb the contaminants.
• In adsorption, contaminants are trapped on the surface of the substance, but not ingested into the substance.
• Activated carbon filters work by the principle of adsorption.
• Dialysis is a process for the removal of waste and excess water from the blood, and is not typically used in water purification.

A sol is a colloidal suspension of very small solid particles in a continuous liquid medium. Sol particles typically have a charge that can be positive or negative, depending on the type of sol and the conditions of its preparation.

Among the options you provided:

• Starch - Typically, starch sols are negatively charged.
• Gum - Gum-based sols are generally not characterized by a specific charge without more context, but they are usually not particularly known for carrying a positive charge.
• Gold Sol - Gold sols are negatively charged. However, without specifying the stabilizing agent or the preparation method, we cannot definitively say it's positively charged. Historically, negatively charged gold sols are more commonly mentioned in literature due to the stabilizing agents commonly used.
• Blood is a positively charged colloid whereas sols of starch, gum & gold are negatively charged. 

Concept:

• A catalyst is a substance that can be added to a reaction to enhance the reaction rate without getting consumed in the process.
• Catalysts typically speed up a reaction by lowering the activation energy or changing the reaction mechanism.
• Enzymes are proteins that act as catalysts in biochemical reactions.
• A stoichiometric amount of one reactant can mean the amount that will react completely with a given amount of another reactant, leaving no excess of either one.
• Catalyst does not take part in balancing the chemical reaction hence catalysts are not required in Stoichiometric amounts.
• Most common catalysts are - Aluminosilicates, Iron, Vanadium, Nickel, Platinum + Alumina.

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​Shape selective catalysts:

• Some catalysis reactions depend upon the pore size of the reactant and the shape of catalyst used.
• The pore size and shape of catalysts is similar to the shape and size of the reactants then they can fit into each other and the reaction takes place.
• Zeolites are for example are shape-selective catalysts. They can catalyze only selective reactions.
• The pore size of Zeolites do not permit all transition state complex to pass through it, thus becomes selective in nature.
• Zeolites are large network of aluminosilicates having the network type Al-O-Si. Molecules like water and alkali metals are trapped inside the pores of the networks.

Explanation:

• Zeolites, a shape selective catalyst or HZSM-5 are the catalysts used in conversion of alcohols to gasoline.
• The temperature range is 300-400^oC.
• The alcohols first undergo dehydration to give unsaturated alkenes.
• The alkenes are then converted to higher alkenes via hydrogenation.
• The catalyst used in Haber's process synstesis of ammonia is Fe.
• It increases the rate of reaction between nitrogen and hydrogen.
• Finely divides solid Fe provides a surface for the reaction to occur.
• Gases nitrogen and hydrogen get adsorbed on the catalyst surface, a reaction occurs, and then the products diffuse out.
• catalysts used for synthesis of methanol from CO and H2 are copper and nickel.
• The catalyst used in polymerisation of ethelene is Zeigler-Natta catalyst.

Hence, a shape selective catalyst used in conversion of alcohol to gasoline.

Concept:

Adsorption is defined as the deposition of molecular species onto the surface.
The molecular species that gets adsorbed on the surface is known as Adsorbent and the surface on which adsorption occurs is known as Adsorbate.

Types of Adsorption

On the basis of interaction forces between adsorbate and adsorbent, adsorption is of two types. 

Physical adsorption:

This type of adsorption is also known as physisorption. It is due to weak Van der Waals forces between adsorbate and adsorbent. 

For example, H2 and N2 gases adsorb on coconut charcoal.

Chemical adsorption:

This type of adsorption is also known as chemisorption. It is due to strong chemical forces of bonding type between adsorbate and adsorbent.

We can take the example involving the formation of iron nitride on the surface when iron is heated in N2 gas at 623 K. 

Additional Information

Adsorption of gas on a solid is a spontaneous exothermic reaction.

Amount of heat liberated when a unit mass of a gas is adsorbed on the surface is called heat of adsorption.

The process of removal of adsorbent from the surface of adsorbate is known as Desorption.

Concept:

1. Colloidal medicines:

Medicines are more effective in colloidal state because colloids have a larger surface area. Thus, they get easily assimilated, absorbed and digested.

Thus, option (a) is wrong.

2. Addition of alum:

Alum is used in the form of Aluminium Sulphate (usually) to remove particulates in water through flocculation to remove solids and some ions and allow them to be filtered or settled. This process is a part of water treatment process.

Excess of alum can make water unfit for drinking but in terms of excess is not mentioned in the option.

Thus, option (b) is wrong.

3. Electrophoresis:

The coagulation of lyophobic sols can be done by electrophoresis where the colloidal particles move towards oppositely changed electrodes which gets discharged and forms precipitate.

Thus, option (c) is correct.

4. Brownian motion:

The viscosity is also inversely proportional to the speed of Brownian motion. So, lesser the viscosity, faster the motion.

Thus, option (d) is wrong.

Concept:

Types of Mixtures:

Homogeneous Mixture:

• Those mixtures, in which the substances are completely mixed together and are indistinguishable from one another, are called homogeneous mixtures.
• For example Soda water, Soft drinks, lemonade, salt or sugar solution, etc.

Heterogeneous Mixture:

• Those mixtures in which the substances remain separate and one substance is spread throughout the other substance as small particles, droplets, or bubbles are called heterogeneous mixtures.
• All the suspensions and colloids are heterogeneous mixtures.
• A mixture is heterogeneous and shows Tyndall effect because of the floating particle it behave like colloid solution or scatter light but actually its heterogeneous mixture the particle will settle down after some time and the tyndel effect will diminish hence it doesnt scatter light when particle settle down.
• For Example: - Sugar and sand mixture, muddy river water, soap solution. 

​Explanation:

Colloids:

• A colloid is a heterogeneous system in which one substance is dispersed (dispersed phase or colloidal particles) in another substance which is called a dispersion medium.

Properties of colloids:

• A colloid appears to be homogeneous but actually, it is heterogeneous.
• The particles of most of the colloids cannot be seen even with a microscope.
• It scatters a beam of light passing through it (Tyndall effect).
• The size of the solute particle is in the range of 1 to 100 nm.
• Since they are heterogeneous in nature, centrifugation techniques can be used to separate the particles.

The correct answer is Ultra-filtration.

Key Points

• The method in which the process of separating the colloidal particles from the solvent and soluble solutes present in the colloidal solution by specially prepared filters, which are permeable to all substances except the colloidal particles is known as Ultra-filtration.
• The blood is filtered through three layers i.e., the endothelium of glomerular blood vessels, the epithelium of Bowman’s capsule (podocyte cells), and a basement membrane between these two layers.
• This type of filtration is called Ultra-filtration. 

Additional Information

• Vacuum filtration is a mechanical method of dewatering sludge and Incineration units are used for the disposal of dewatered sludge.
• Dialysis works on the principle of the diffusion of solutes and ultra-filtration of fluid across a semi-permeable membrane.
  • Diffusion is a property of substances in water; substances in water tend to move from an area of high concentration to an area of low concentration.
• Electro Dialysis (ED) is a membrane process, during which ions are transported through a semi-permeable membrane, under the influence of an electric potential.

Concept:

Adsorption:

• Adsorption is defined as the deposition of molecular species onto the surface.
• The molecular species that gets adsorbed on the surface is known as Adsorbent and the surface on which adsorption occurs is known as Adsorbate.
• It is a surface phenomenon and occurs due to the unsaturation of forces on the surface of an adsorbate molecule.

​

• There are two types of adsorption:
  • Physical or physisorption where there exist only weak van der Waals forces between adsorbent and adsorbate.
  • Chemical or chemisorption where new bonds are formed between adsorbent and adsorbate.

Explanation: 

• In adsorption isotherms, the fraction of moles of adsorbate (x) by the grams of adsorbent(m) versus P is plotted.
• The Freundlich isotherm gives us the empirical relationship between the amount of gas adsorbed and its equilibrium pressure P.
• It is seen that the amount of adsorption increases with an increase of pressure when the pressure is in the lower range.
• As the pressure increases, the rate of adsorption increases but reaches saturation after some point.
• After this point, the amount of adsorption doesn't change even when pressure is increased.
• The equation of Freundlich isotherm is given as follows:

\(\frac{{\rm{x}}}{{\rm{m}}} \propto {\rm{\;}}{{\rm{P}}^{\frac{1}{{\rm{n}}}}}\) where k and n are constant for a particular adsorbent and adsorbate at a fixed temperature.

• The graph is represented as follows.

• When the temperature is fixed and pressure is low, the adsorption becomes directly proportional to the pressure of the gas.
• The relation reduces to
• x=kP.

This signifies, 1/n = 1 or n = 1.

• At a higher range of pressure, the adsorption becomes independent of pressure and the equation reduces to

x/m= k.

We can infer from this that 1/n = 0.

Hence, in Freundlich adsorption isotherm, the value of 1/n is 0 to 1.

Explanation:

An emulsion is a type of colloid in which one liquid is dispersed in another immiscible liquid in the form of small droplets.

Hair cream is an example of an emulsion where oil droplets are dispersed in water. Paint can also be classified as an emulsion or a suspension depending on the type of paint.

Cheese, on the other hand, is a type of colloid where solid particles are dispersed in a liquid. Smoke is an aerosol, which is a type of colloid where solid or liquid particles are suspended in a gas.