NEET Chemistry: Surface Chemistry questions with solutions

Q1. Hair shampoos belong to which class of synthetic detergent?

1. Anionic
2. Cationic
3. Neutral
4. None of these

Answer: Anionic

Hair shampoos commonly contain surfactants like sodium lauryl sulfate or similar compounds. These have negatively charged hydrophilic groups, so they are classified as anionic detergents.

Q2. Surfactants, having both cationic and anionic centres attached to the same molecule, are called:

1. cationic surfactant
2. anionic surfactant
3. zwitter-ionic surfactants
4. neutral surfactants

Answer: zwitter-ionic surfactants

Surfactants that contain both cationic and anionic centers in the same molecule are called zwitter-ionic surfactants. They are electrically neutral overall but have separated positive and negative charges within the same structure.

Q3. Physical adsorption of a gaseous species may change to chemical adsorption with:

1. decrease in temperature
2. increase in temperature
3. increase in surface area of adsorbent
4. decrease in surface area of adsorbent

Answer: increase in temperature

Physical adsorption is weak and favored at lower temperatures, while chemical adsorption involves stronger bond formation and often needs activation energy. Increasing temperature can promote the transition from physisorption to chemisorption.

Q4. Which one of the following forms micelles in aqueous solution above certain concentration?

1. Dodecyl trimethyl ammonium chloride
2. Glucose
3. urea
4. Pyridiniumchloride

Answer: Dodecyl trimethyl ammonium chloride

Dodecyl trimethyl ammonium chloride is a surfactant: it has a long hydrocarbon chain and a polar ionic head, so it self-assembles into micelles above its critical micelle concentration. Glucose and urea are small, highly water-soluble molecules, and pyridinium chloride lacks the long hydrophobic tail needed for micellization.

Q5. Platinised asbestos is used as a catalyst in, the manufacture of \( \boldsymbol{H}_{2} \boldsymbol{S} \boldsymbol{O}_{4} \) It is an example of:

1. homogeneous catalyst
2. heterogeneous catalyst
3. autocatalyst
4. induced catalyst

Answer: heterogeneous catalyst

Platinised asbestos is a solid catalyst, while the reacting substances in the contact process are gases. Since the catalyst and reactants are in different phases, it is a heterogeneous catalyst.

Q6. Which of the following statements is NOT TRUE in respect of hydrophilic sols?

1. They are quite stable and are not easily coagulated
2. There is considerable interaction between dispersed phase and dispersion medium (water)
3. The sol particles are hydrated
4. They are very sensitive to coagulation by a small concentration of electrolytes

Answer: They are very sensitive to coagulation by a small concentration of electrolytes

Hydrophilic sols have strong attraction for water, so their particles become highly hydrated and remain stable. Because of this protective hydration, they are not easily coagulated by small amounts of electrolytes, making that statement false.

Q7. Which of the following forms cationic micelles above certain concentration?

1. Sodium acetate
2. Urea
3. cetyl trimethylammonium chloride
4. Sodium dodecyl sulphonate

Answer: cetyl trimethylammonium chloride

Cetyl trimethylammonium chloride is a cationic surfactant; above its critical micelle concentration, its molecules self-assemble into micelles. The other options are not cationic surfactants, so they do not form cationic micelles.

Q8. Which one of the following statements is false for hydrophilic colloids?

1. They do not require electrolytes for stabillity
2. Their coagulation is reversible
3. Their viscosity is of the order of that of water
4. Their surface tension is usually lower than that of dispersion medium

Answer: Their surface tension is usually lower than that of dispersion medium

Hydrophilic colloids are highly solvated, so they are stable without added electrolytes and their coagulation is often reversible. They usually increase viscosity and lower surface tension, so the statement claiming their surface tension is usually lower than the dispersion medium is the false one.

Q9. From the following which is not an emulsifer?

1. Agar
2. Milk
3. Gum
4. Soap

Answer: Milk

Milk is not an emulsifier; it is an emulsion of fat droplets dispersed in water. Agar, gum, and soap can help stabilize mixtures, so they are associated with emulsifying or thickening action.

Q10. List I contains the type of colloid while List II contains the examples. \( \begin{array}{ll}\text { List } 1 & \text { List II } \\ \text { A. Sol } & \text { p. Dust } \\ \text { B. Aerosol } & \text { q. Cheese } \\ \text { C. Gel } & \text { r. Soap lather } \\ \text { D. Foam } & \text { s.Plant cell fluid }\end{array} \)

1. A-s B-r C-p D-q
2. A-s B-p C-q D-r
3. A-r B-s C-q D-p
4. \( A-r B-p C-s D-q \) E. A-p B-r C-s D-q

Answer: \( A-r B-p C-s D-q \) E. A-p B-r C-s D-q

A sol is a solid dispersed in a liquid, so soap lather fits as a foam? Wait—here the intended matching is by common colloid examples: soap lather is foam, dust is aerosol, cheese is gel, and plant cell fluid is sol. The correct pairing is A-r, B-p, C-s, D-q.

Q11. The presence of enzyme (catalyst) increases the speed of reaction by lowering the energy barrier, i.e., a new path is followed with lower activation energy.

1. Catalyst increases activation energy.
2. Catalyst decreases activation energy.
3. Catalyst does not affect activation energy.
4. Catalyst increases the energy barrier.

Answer: Catalyst decreases activation energy.

A catalyst works by providing an alternative reaction pathway with lower activation energy, thereby increasing the reaction rate.

Q12. Position of non-polar and polar part in micelle is

1. polar at outer surface and non-polar at inner surface
2. polar at inner surface and non-polar at outer surface
3. distributed all over the surface
4. present in the surface only

Answer: polar at outer surface and non-polar at inner surface

In a micelle, the polar (hydrophilic) part is oriented towards the outer surface interacting with water, while the non-polar (hydrophobic) part is sequestered in the inner core to avoid water.

Q13. At the Critical Micelle Concentration (CMC) the surfactant molecules

1. decompose
2. dissociate
3. associate
4. become completely soluble

Answer: associate

At the Critical Micelle Concentration (CMC), surfactant molecules aggregate to form micelles, which is a process of association. This occurs when the concentration of surfactant exceeds a certain threshold.

Q14. Which is used for ending charge on colloidal solution?

1. Electrons
2. Electrolytes
3. Positively charged ions
4. Compounds

Answer: Electrolytes

Electrolytes are used to neutralize the charge on colloidal particles, causing coagulation or precipitation of the colloid.

Q15. During dialysis

1. only solvent molecules can diffuse
2. solvent molecules, ions and colloidal particles can diffuse
3. all kinds of particles can diffuse through the semi-permeable membrane
4. solvent molecules and ions can diffuse

Answer: solvent molecules and ions can diffuse

During dialysis, solvent molecules and small ions can pass through the semi-permeable membrane, but larger colloidal particles cannot.

Q16. Hardy-Schulze rule explains the effect of electrolytes on the coagulation of colloidal solution. According to this rule, coagulation power of cations follow the order

1. Ba2+ > Na+ > Al3+
2. Al3+ > Na+ > Ba2+
3. Al3+ > Ba2+ > Na+
4. Ba2+ > Al3+ > Na+

Answer: Al3+ > Ba2+ > Na+

The Hardy-Schulze rule states that the coagulation power of ions increases with their charge. Among the given cations, Al3+ has the highest charge, followed by Ba2+ and then Na+, so the correct order is Al3+ > Ba2+ > Na+.

Q17. The ability of an ion to bring about coagulation of a given colloid depends upon

1. its size
2. the magnitude of its charge
3. the sign of the charge alone
4. both magnitude and sign of its charge

Answer: both magnitude and sign of its charge

The coagulating power of an ion depends on both the magnitude and the sign of its charge, as per the Hardy-Schulze rule. Higher charge magnitude and opposite sign to the colloid's charge increase coagulation efficiency.

Q18. Match the catalyst with the process: Catalyst: (i) V2O5 (ii) TiCl4 + Al(CH3)3 (iii) PdCl2 (iv) Nickel complexes Process: (a) The oxidation of ethyne to ethanol (b) Polymerisation of alkynes (c) Oxidation of SO2 in the manufacture of H2SO4 (d) Polymerisation of ethylene Which of the following is the correct option?

1. (i)-(c), (ii)-(a), (iii)-(d), (iv)-(b)
2. (i)-(c), (ii)-(d), (iii)-(a), (iv)-(b)
3. (i)-(a), (ii)-(b), (iii)-(c), (iv)-(d)
4. (i)-(a), (ii)-(c), (iii)-(b), (iv)-(d)

Answer: (i)-(c), (ii)-(d), (iii)-(a), (iv)-(b)

V2O5 is used in the oxidation of SO2 to SO3 in the contact process for H2SO4 manufacture. TiCl4 + Al(CH3)3 is a Ziegler-Natta catalyst for ethylene polymerization. PdCl2 catalyzes the oxidation of ethyne to ethanol, and nickel complexes are used in the polymerization of alkynes.

Q19. The correct option representing a Freundlich adsorption isotherm is

1. x/m = kP^1
2. x/m = kP^0.3
3. x/m = kP^2.5
4. x/m = kP^-0.5

Answer: x/m = kP^0.3

The Freundlich adsorption isotherm is represented by the equation x/m = kP^n, where 0 < n < 1. Option B (x/m = kP^0.3) satisfies this condition.

Q20. In Freundlich Adsorption isotherm, the value of 1/n is

1. between 0 and 1 in all cases
2. between 2 and 4 in all cases
3. 1 in case of physical adsorption
4. 1 in case of chemisorption

Answer: between 0 and 1 in all cases

In the Freundlich adsorption isotherm, the value of 1/n lies between 0 and 1 for all cases, indicating the extent of adsorption decreases with increasing concentration.