Surface Chemistry: JEE Advanced PYQ, 2007–2026

Q1 · Chemistry · Surface Chemistry

A gas adsorbs on a solid according to x/m = k p^(1/2), where x/m is in mg g⁻¹ and p is in atm. The constant k is 4 mg g⁻¹ atm^(-1/2). What is x/m, in mg g⁻¹, when p = 9 atm?

• A4.5 mg g⁻¹
• B12 mg g⁻¹
• C36 mg g⁻¹
• D2.25 mg g⁻¹

Q2 · Chemistry · Surface Chemistry

Sodium stearate removes an oily stain from cloth during washing. Which description of the cleansing action is correct?

• AThe carboxylate group reacts chemically with the grease to form a water-soluble salt that rinses away
• BThe ionic heads dissolve in the oil droplet while the hydrocarbon tails stay in water, which gives a stable emulsion
• CThe hydrocarbon tails embed in the oil droplet and the negatively charged heads face the water, so the mutually repelling droplets stay suspended and wash away
• DSoap only lowers the surface tension of water so that oil dissolves in it as individual molecules

Q3 · Chemistry · Surface Chemistry

A clean metal powder is exposed at 300 K to a gas that is chemisorbed on it, until the surface is saturated with a chemisorbed monolayer. The vessel is evacuated, cooled to 77 K, and the same gas is admitted again at a pressure close to its saturation vapour pressure at 77 K. At 77 K the gas can also be physisorbed. Which statement correctly describes what happens?

• ANo further uptake can occur, because chemisorption saturates the available surface valences and leaves no site for any further adsorption
• BFurther gas is held by weak van der Waals forces as additional layers over the chemisorbed monolayer, and this physisorbed gas can be removed by warming and evacuating while the chemisorbed layer remains
• CA second chemisorbed layer forms, because lowering the temperature favours the exothermic chemisorption
• DFurther uptake occurs only if the chemisorbed monolayer is first displaced, because physisorption and chemisorption cannot share a surface

Q4 · Chemistry · Surface Chemistry

In the Freundlich adsorption isotherm x/m = k p^(1/n), what is the dependence of x/m on p when n = 1?

• Ax/m is inversely proportional to p
• Bx/m is directly proportional to p
• Cx/m is proportional to the square root of p
• Dx/m is independent of p

Q5 · Chemistry · Surface Chemistry

Equal masses of activated charcoal are exposed to H₂ (critical temperature 33 K), CH₄ (191 K), CO₂ (304 K) and NH₃ (405 K) separately, each at the same temperature of 300 K and the same pressure. Which order correctly gives increasing extent of adsorption?

• AH₂ < CH₄ < CO₂ < NH₃
• BH₂ < CH₄ < NH₃ < CO₂
• CNH₃ < CO₂ < CH₄ < H₂
• DCH₄ < H₂ < NH₃ < CO₂

Q6 · Chemistry · Surface Chemistry

A fixed mass of finely divided nickel is exposed to dihydrogen at constant pressure, and the amount taken up is measured from about 80 K to 600 K. As temperature rises, the amount adsorbed first falls steadily, then rises to a maximum at a considerably higher temperature, and finally falls again. Which interpretation of this adsorption isobar is correct?

• AThe first fall is weakening of exothermic physisorption of H₂ molecules. The rise is activated chemisorption (dissociation to H atoms on Ni), which becomes fast enough only at higher temperature. The final fall is the exothermic chemisorption equilibrium shifting back towards desorption.
• BThe first fall is chemisorption weakening. The rise is physisorption, which is endothermic and so favoured by heating. The final fall is the physisorbed layer evaporating.
• CThe whole curve is due to physisorption alone. The rise at intermediate temperature occurs because faster molecules collide with the surface more often and so build up multilayers.
• DThe first fall and the rise both belong to chemisorption. The rise appears because heating creates additional surface area on the nickel, and the final fall is physisorption starting.

Q7 · Chemistry · Surface Chemistry

Which plot of experimental data gives a straight line whose slope equals 1/n for the Freundlich adsorption isotherm x/m = k p^(1/n)?

• Ax/m against p
• Bx/m against 1/p
• Clog(x/m) against log p
• Dp against log(x/m)

Q8 · Chemistry · Surface Chemistry

A freshly precipitated, washed precipitate of iron(III) hydroxide is shaken with a very small amount of dilute FeCl₃ solution. The precipitate gradually goes into a stable reddish-brown sol. Which statement correctly explains this change?

• AThe precipitate preferentially adsorbs Fe³⁺ ions, which are common to its lattice. The particles acquire a positive charge, and mutual repulsion breaks the aggregates into colloidal particles.
• BThe precipitate adsorbs Cl⁻ ions from FeCl₃ and becomes negatively charged. The repulsion between negatively charged particles disperses it as a negative sol.
• CFe(OH)₃ reacts chemically with FeCl₃ to form a soluble basic chloride, so the result is a true solution of ions rather than a sol.
• DThe added electrolyte compresses the electrical double layer around the particles, and the reduced repulsion lets the particles disperse in the medium.

Q9 · Chemistry · Surface Chemistry

The gold number of a protective colloid is the mass in milligrams that just prevents coagulation of 10 mL of a standard gold sol on adding 1 mL of 10% NaCl solution. Protective colloid A has gold number 0.04 and protective colloid B has gold number 20. What mass of A gives the same protective effect on a gold sol as 10 mg of B?

• A0.02 mg
• B0.04 mg
• C0.08 mg
• D5000 mg

Q10 · Chemistry · Surface Chemistry

Which kind of interaction mainly holds a gas molecule to a solid surface in physisorption?

• ACovalent bonds formed between the gas molecule and surface atoms
• BWeak van der Waals forces
• CIonic bonds from complete electron transfer to the surface
• DMetallic bonding with the conduction electrons of the solid