Is Surface Chemistry part of the EAPCET Chemistry syllabus?

Yes. Surface Chemistry is taught in Intermediate second year Chemistry, and the EAPCET Engineering syllabus is based on the Intermediate first- and second-year syllabus. Check the official notification each year for any changes.

How many Chemistry questions are there in EAPCET?

40 of the 160 questions in the Engineering paper are Chemistry, spread across 24 chapters.

What mistakes do students make in Surface Chemistry?

Ranking coagulating power by the cation for a positive sol — for Fe(OH)₃ count the anion’s charge; use cations only for negative sols such as As₂S₃. Saying adsorption is endothermic or that physisorption increases with temperature — adsorption is exothermic and physisorption falls as temperature rises. Calling chemisorption multilayer — chemisorption gives a monolayer, while physisorption can form multilayers. Thinking a smaller coagulation value means weaker coagulating power — coagulation value is the minimum concentration needed, so the smaller it is, the stronger the electrolyte.

EAPCET Chemistry · Intermediate second year

Surface Chemistry

Surface Chemistry covers adsorption, catalysis, colloids and emulsions.

Subject: Chemistry
Taught in: Intermediate second year
Chemistry in the paper: 40 of 160 questions

Key formulas and results

Physisorption is weak and reversible; chemisorption is strong and specific
Freundlich isotherm: $\frac{x}{m} = k p^{1/n}$
Colloids show the Tyndall effect and Brownian motion
Hardy–Schulze rule: coagulating power rises with the charge of the ion
Enzymes are highly specific biological catalysts

What this chapter covers

Physisorption and chemisorption
Adsorption isotherms
Catalysis
Colloids and their classification
Properties of colloids
Emulsions

How it is usually asked

Types of adsorption
Order of coagulating power
Properties of colloids
Types of catalysis

Understanding Surface Chemistry

Adsorption is the accumulation of molecules on a surface, unlike absorption, where they spread through the bulk. It is always exothermic, and it increases with surface area and with how easily a gas liquefies, so NH₃ and SO₂ are adsorbed more than H₂ or N₂. Physisorption relies on weak van der Waals forces (about 20–40 kJ mol⁻¹), is reversible, forms multilayers and falls with rising temperature. Chemisorption forms chemical bonds (about 80–240 kJ mol⁻¹), is specific, forms a single layer and is often irreversible.

The Freundlich isotherm, x/m = k p^(1/n) with n > 1, describes how the amount adsorbed per gram rises with pressure; plotting log(x/m) against log p gives a straight line of slope 1/n and intercept log k. Catalysis builds on adsorption. In heterogeneous catalysis, such as iron in the Haber process, reactants are adsorbed on the catalyst surface. Enzymes are biological catalysts that are highly specific and work best near body temperature and a particular pH. Zeolites act as shape-selective catalysts.

Colloids contain particles of roughly 1–1000 nm dispersed in a medium. Lyophilic sols such as starch and gelatin are stable and reversible; lyophobic sols such as gold, As₂S₃ and Fe(OH)₃ need stabilising and coagulate easily. Colloidal particles scatter light (Tyndall effect), move randomly (Brownian motion) and carry charge, which is shown by electrophoresis. By the Hardy–Schulze rule, the ion of opposite charge coagulates a sol more strongly the higher its charge. Emulsions are liquid-in-liquid colloids: milk is oil-in-water and butter is water-in-oil.

Worked example

EAPCET-style question

A positively charged $\ce{Fe(OH)3}$ sol is most effectively coagulated by which of the following electrolytes?

(1) $\ce{NaCl}$
(2) $\ce{Na2SO4}$
(3) $\ce{Na3PO4}$
(4) $\ce{K4[Fe(CN)6]}$

Solution

$\ce{Fe(OH)3}$ sol (made by hydrolysing $\ce{FeCl3}$ ) is positively charged, so the anions of the electrolyte cause coagulation.
The anions are $\ce{Cl-}$ (charge 1), $\ce{SO4^2-}$ (2), $\ce{PO4^3-}$ (3) and $\ce{[Fe(CN)6]^4-}$ (4).
Hardy–Schulze rule: coagulating power increases with the charge of the oppositely charged ion.
Order: $\ce{[Fe(CN)6]^4-} > \ce{PO4^3-} > \ce{SO4^2-} > \ce{Cl-}$ , so $\ce{K4[Fe(CN)6]}$ is the most effective.
The $\ce{Na+}$ and $\ce{K+}$ cations carry the same charge as the sol and play no part.

Answer: $\ce{K4[Fe(CN)6]}$

Common mistakes to avoid

Ranking coagulating power by the cation for a positive sol — for Fe(OH)₃ count the anion’s charge; use cations only for negative sols such as As₂S₃.
Saying adsorption is endothermic or that physisorption increases with temperature — adsorption is exothermic and physisorption falls as temperature rises.
Calling chemisorption multilayer — chemisorption gives a monolayer, while physisorption can form multilayers.
Thinking a smaller coagulation value means weaker coagulating power — coagulation value is the minimum concentration needed, so the smaller it is, the stronger the electrolyte.

How to prepare it

The Hardy–Schulze ordering is asked often — practise ranking ions by charge.

Once the formulas feel familiar, test them the way the exam does: practise Surface Chemistry questions chapter-wise, then attempt a full previous year paper to see whether it holds up under a 3-hour timer.

Related Chemistry chapters

See every chapter in the EAPCET Chemistry syllabus.

Practise Surface Chemistry chapter-wise

Chapter-wise quizzes show exactly which topics in this chapter you still get wrong — before a full paper does.

Frequently asked questions

Is Surface Chemistry part of the EAPCET Chemistry syllabus?: Yes. Surface Chemistry is taught in Intermediate second year Chemistry, and the EAPCET Engineering syllabus is based on the Intermediate first- and second-year syllabus. Check the official notification each year for any changes.
How should I prepare Surface Chemistry for EAPCET?: The Hardy–Schulze ordering is asked often — practise ranking ions by charge.
How many Chemistry questions are there in EAPCET?: 40 of the 160 questions in the Engineering paper are Chemistry, spread across 24 chapters.
What mistakes do students make in Surface Chemistry?: Ranking coagulating power by the cation for a positive sol — for Fe(OH)₃ count the anion’s charge; use cations only for negative sols such as As₂S₃. Saying adsorption is endothermic or that physisorption increases with temperature — adsorption is exothermic and physisorption falls as temperature rises. Calling chemisorption multilayer — chemisorption gives a monolayer, while physisorption can form multilayers. Thinking a smaller coagulation value means weaker coagulating power — coagulation value is the minimum concentration needed, so the smaller it is, the stronger the electrolyte.