DGT Surface Chemistry
DGT Surface Chemistry
DGT Surface Chemistry
Scientists Contributions
Johannes Van der Waals (1837 - 1923) i. Deduced Van der Waals equation of state and
(Dutch scientist) introduced a term Van der Waals forces of
attraction. These are generally inter molecular
forces
ii. Received Nobel prize in physics in 1910.
Freundlich, Herbert Max Finlay (1880 - 1941) i. Introduced the term thixotropy that describes a
(German chemist) specific behaviour of gels.
ii. Proposed an equation which is known as
Freundlich adsorption isotherm.
iii. Studied the electrical properties of colloids.
Arne Wilhelm Kaurin Tiselius (1902 - 1971) i. Carried out first important experiment on
(Swedish physical chemist) electrophoresis in 1930s which proved to be a
powerful technique for studying mixtures of
proteins.
ii. Received Nobel prize in chemistry for his work
on electrophoresis.
7.1 : Introduction :
Q.1. Define surface.
Ans: A boundary separating two phases is called a surface or interface.
eg. A boundary between water and its vapour. This is a liquid gas interface.
Note:
Surfaces differ from the phases in some properties. Also many properties of solids, liquids or solutions can
be explained by the action of their surfaces.
eg. Surface of solid or liquid has strong affinity for the particles (atoms or molecules) of the substances
that are coming in contact with it.
7.2 : Adsorption :
Q.2. Define:
i. Adsorption ii. Desorption iii. Adsorbate
iv. Adsorbent v. Heat of adsorption vi. Absorption
vii. Absorbate viii. Absorbent
Ans: i. Adsorption: Adsorption is defined as the phenomenon of accumulation of higher concentration of
one substance on the surface of another than in the bulk.
eg. Water vapours are adsorbed by silica gel.
ii. Desorption: The process of removal of an adsorbed substance from the surface is known as
desorption.
iii. Adsorbate: The substance adsorbed on the surface of another substance is called an adsorbate or
adsorbed phase.
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 2
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 3
Q.9. What is chemisorption? What are its characteristics? Give two examples of chemisorption.
OR
Write a short note on chemisorption.
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 4
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 5
Q.11. Which are the various factors on which adsorption of gases on solid depends?
Ans: Adsorption of gases on solid depends on the following factors:
i. Nature of adsorbate (gas)
ii. Nature of solid adsorbent
iii. Surface area of adsorbent
iv. Temperature of the surface
v. Pressure of the gas
Note:
All solids adsorb gases to some extent but when the adsorbent provides large surface area for a given
mass, adsorption occurs to a significant extent.
Q.12.How does adsorption of gases by solids depend on the nature of the adsorbate?
Ans: i. Critical temperature is a certain minimum temperature that is required for the liquefaction of a gas.
Above this temperature a gas cannot be liquefied.
ii. It is observed that volume of gas adsorbed (i e., extent of adsorption) increases as the critical temperature
of the gas increases.
iii. However, higher the critical temperature of a gas, more easily it will be liquified.
iv. Thus, it implies that the gases which are easily liquified are easily adsorbed and adsorption of gases by
solids depend on the nature of adsorbate (i.e., whether it is easily liquefiable or not)
eg. The gases which are easily liquefiable (like SO2, Cl2, NH3, etc.,) are adsorbed to a greater extent
than the gases which cannot be easily liquified (like N2, O2, H2, etc.).
Note:
Critical temperature of gases and volume adsorbed.
Volume of gas
adsorbed (cm 3 )
Gas Critical by 1 g of
temperature (K) charcoal at
15o C
Dinitrogen 126 08
(N 2 )
Hydrogen 324 72
chloride (HCl)
Ammonia 406 181
(NH3 )
Chlorine 417 235
(Cl 2 )
Sulphur 430 380
dioxide (SO 2 )
Q.13. How does adsorption of gases by solids depend on nature of the adsorbent?
Ans: i. Adsorbent with more free valencies or unbalanced forces show more tendency to adsorb.
eg. Transition metals like Ni, Pd, Pt, etc.
ii. Also solids having porous nature provide large surface area for a given mass and are found to be
effective adsorbents.
eg. Silica gel, charcoal, etc.
Q.14. How does adsorption of gases by solids depend on surface area of the adsorbent?
Ans: i. Adsorption is a surface phenomenon. Hence, with the increase in the surface area of adsorbent for a
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 6
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 7
7.3 : Catalysis :
Introduction:
Q.20. Explain catalysis with a suitable example.
Ans: i. A catalyst is defined as a substance which when added to the reacting system increases the rate of
the reaction without itself being consumed in the reaction.
ii. Thus, the phenomenon of increasing the rate of a chemical reaction with the help of a catalyst is
known as catalysis.
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 8
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 9
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 10
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 11
I ( aq )
1
H2O2(aq) H2O(l) + 2 O2(g)
Hydrogen water
peroxide
ii. The formation of SO3, in lead chamber process for the manufacture of H2SO4, is catalyzed by nitric
oxide or nitrogen dioxide.
1 NO( g )
SO2(g) + O2(g)
or NO2 ( g )
SO3(g)
2
Sulphur Sulphur
dioxide trioxide
The catalyst and the reactants are present in the same gaseous phase.
Q.31. Explain acid catalysis with suitable examples.
Ans: When the reaction is catalysed due to the presence of an acid, it is called as acid catalysed reaction.
eg.
i. Hydrolysis of an ester: Ester when hydrolysed with water forms corresponding organic acid and
alcohol. The reaction is catalysed by an acid like HCl
CH3COOC2H5(aq) + H2O(l) H ( aq )
CH3COOH(aq) + C2H5OH(aq)
Ethyl acetate Acetic acid Ethanol
(Ester) (Organicacid) (Alcohol)
ii. Alkylation of benzene: Benzene on reaction with alkene in the presence of acid undergoes alkylation
and forms corresponding alkyl benzene
C6H6(l) + C2H4(l) H ( aq )
C6H5CH2CH3
Benzene Ethene Ethyl benzene
In both of the above reactions, catalyst and reactants are present in liquid phase. Thus, the catalyst is
homogeneous catalyst and the phenomenon of catalysis is homogeneous catalysis.
Q.32. Explain the industrial and domestic applications of homogeneous catalysts.
Ans: i. Industrial applications: Homogeneous catalysts are used in industrially important reactions like
polymerization, carbonylation, etc.
ii. Domestic applications: Detergents used for washing purposes contain enzymes which catalyze oxidation
and depolymerization of stains. Metal atoms present in cleansers act as catalyst and enhance the
bleaching action.
Q.33. What are heterogeneous catalysts? Give two examples.
Ans: A catalyst which exists in different phase from the reactants is known as heterogeneous catalyst.
eg.
i. The hydrogenation of unsaturated compounds is catalyzed by finely divided metals like Ni, Pd or Pt.
PtorPd
H2C = CH2(g) + H2(g)
or Ni
H3C – CH3(g)
Ethene Ethane
This principle is used in the food industry for the conversion of unsaturated vegetable oils to solid fats.
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 12
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 13
Q.42. Classify the following catalyzed reactions as homogencous and heteroreneous catalysis :
Ans:
Homogeneous catalysis Heterogeneous catalysis
ZnO and
Tl+(aq) + 2Ce4+(aq)
Ag 3+ 3+
Tl (aq) + 2Ce (aq) CO(g) + H2O(g)
CuO
CO2(g) + H2(g)
TiO2
4NH3(g) + 4NO(g) + O2(g) 4N2(g) + 6H2O(l)
Ru
H
C 12H 22O 11(aq) +H 2O (l) C 6H 12O 6(aq)+ C6H 12O 6(aq) 2NO(g) + 2CO(g)
Al2 O3
N2(g) + 2CO2(g)
Glucose Fructose
carboxyl esterase
CH3COOC2H5(aq) + H2O(l)
enzyme 4NH3(g) + 7O2(g)
Pt gauze
4NO2(g) + 6H2O(l)
CH3COOH(aq) + C2H5OH(aq)
C2H6(g)
Pd
C2H4(g) + H2(g)
Catalytic activity :
Q.43. Write a shortnote on catalytic activity. (NCERT)
Ans: i. In heterogeneous catalysis, the activity of a catalyst depends on the strength of chemical adsorption.
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 14
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 15
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 16
v. The active site of the enzyme catalyst binds the substrate (reactant) and produces enzyme-substrate
complex which then decomposes to give the product of reaction and the enzyme is recovered.
E+S ES P+E
Where, E and S are enzyme and substrate respectively. ES is an enzyme-substrate complex and P is
the product.
eg .
i. Decomposition of H2O2 using enzyme catalase as a catalyst:
1
H2O2(aq)
Catalase H2O(l) + O2(g)
2
Hydrogen Water Oxygen
peroxide
ii. Oxidation of Fe2+ ion to Fe3+ ion using ferroxidase enzyme as a catalyst:
4Fe2+(aq) + 4H+(aq) + O2(g)
Ferroxidas 3+
4 Fe (aq) + 2H2O(l)
Note:
i. The lock and key model was developed by German chemist Emil Fischer in 1894.
ii. Nitrogenase enzyme present in bacteria supported by leguminous plants such as peas, beans, etc. act
as a catalyst in the conversion of atmospheric nitrogen to NH3 which serves as a fertilizer for the
growth of plants.
N2 + 3H2 Nitrogenase
2NH3
Nitrogen Ammonia
iii. In the human body, heart and brain cells uses an enzyme called hexokinase, whereas liver cells uses
an enzyme called glucokinase to trap the glucose. The cell reaction can be given as:
Glucose + ATP glucose-6-phosphate + ADP
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 17
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 18
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 19
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 20
Q.62. What are colloids? Why is there no colloid in which both the disperse phase and dispersion
medium are gases?
Ans: i. Colloidal dispersion is defined as the dispersion of small particles (1 nm to 10 3 nm) of one substance
throughout the dispersion medium made of another substance.
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 21
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 22
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 23
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 24
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 25
iv. The lyophobic colloids adsorb the ions of the electrolyte from the solutions in which they are prepared
whereas the lyophilic particles first adsorb the molecules of dispersion medium to form a layer of the
latter od the former. The ions mayor may not be adsorbed on this layer of medium.
v. The charges on the lyophilic particles often result from the ionization of the substance that constitute
the disperse phase.
vi. Evidently, the dispersion medium also carries an electric charge but equal and opposite in sign to that
of the colloidal particles.
vii. Hence, particles and the medium become electrically oppositely charged and consequently the colloidal
system as a whole is electrically neutral.
Q.82. Define electrophoresis. Give its two applications. (NCERT).
Ans: The migration of electrically charged colloidal particles in one direction under the influence of an electric
field is called electrophoresis.
Applications:
i. It is possible to know the sign of charge on the particles. This can be done by observing the direction
of movement of colloidal particles under the influence of an electric field (i.e., during electrophoresis).
If they move to positive electrode, they are negatively charged and vice-versa.
ii. Electrophoresis is used to measure the rate of migration of sol particles.
iii. A mixture of colloidal particles such as proteins can be separated by electrophoresis as different
colloidal particles in a mixture migrate at different rates.
Q.83. Explain phenomenon of electrophoresis using U tube.
Ans: Phenomenon of electrophoresis can be demonstrated by constructing the apparatus as follows:
i. Colloidal dispersion (sol) is taken in U tube and water is added to both arms of U tube. Addition of
water is done slowly and carefully so as to obtain a clear boundary between sol and water.
ii. Two platinum electrodes connected to high voltage battery are inserted in water in two arms of U
tube.
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 26
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 27
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 28
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 29
7.5 : Nanomaterials :
Q.95. Define nanomaterial. State its types.
Ans: The materials having atleast one-dimension in the range of 1 nm to 100 nm are called nanomaterials.
Different types of nanomaterial are as follows:
i. The nanomaterial with only one dimension between 1 nm and 100 nin are called nanolayers.
ii. The nanomaterial with two dimensions in the range 1-100 nm are termed as nanotubes or nanowires.
iii. The nanomaterials with three dimensions in the range of 1 nm to 100 nm are known as nanoparticles.
iv. Quantum dots are semiconductor nanoparticles that are about 1-10 nm in diameter.
Note:
i. Size of nanomaterials lies between the width of 4 - 25 hydrogen atoms laid side by side.
ii. Size of a nanoparticle is about 50,000 times smaller than the diameter of a single strand of human hair
and 1/100th the length of a typical bacterium.
Q.96. What are the different properties ofnanomaterials?
Ans: Properties of nanomaterials:
i. The nanomaterials have different colours than the bulk material.
eg. Gold nanoparticles are red whereas bulk gold metal is yellow.
ii. The nanomaterials have lower melting points than the bulk material.
iii. The nanomaterials tend to have greater reactivity than the bulk material.
eg. Gold nanoparticles are chemically reactive whereas bulk metal is inert.
iv. The nanoparticles have a substantial percentage of atoms on the surface and are therefore bound less
tightly than those within the bulk solid.
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 30
Q.1. Explain the difference in the properties of a surface or an interface and the bulk or a phase. Refer Q.3
Q.2. Explain any two characteristics ofa catalyst. Refer Q.21.
Q.3. Distinguish between:
i. true solution and colloidal dispersion. Refer Q.61.
ii. colloidal dispersion and suspension Refer Q.61.
Q.4. What is coagulation? Give two methods to effect coagulation. Refer Q.87.
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 31
c) k d) kP n
9. Rate of physisorption increases with ______ m P m
a) decrease in temperature 17. When log xlm is plotted against log P, the intercept
b) increase in temperature obtained _______
c) decrease in pressure a) on Y axis is equal to log K
d) decrease in surface area b) on Y axis is equal to K
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 32
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 33
Answer Keys
1. b) 2. d) 3. a) 4. a) 5. c) 6. a) 7. c) 8. a) 9. a) 10. a)
11. a) 12. d) 13. d) 14. c) 15. c) 16. d) 17. a) 18. c) 19. c) 20. a)
21. a) 22. c) 23. b) 24. c) 25. d) 26. c) 27. a) 28. d) 29. c) 30. c)
31. b) 32. d) 33. d) 34. c) 35. b) 36. d) 37. a) 38. a) 39. a) 40. a)
41. b) 42. c) 43. d) 44. a) 45. d)
MH - CET Chemistry - XI
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448
DGT MH –CET 11th CHEMISTRY Study Material 34
DGT Group - Tuitions (Feed Concepts) XIth – XIIth | JEE | CET | NEET | Call : 9920154035 / 8169861448