CBSE Class 12 Chemistry Surface Chemistry Worksheet Set A

Question. Which one of the following characteristics is associated with adsorption?
(a) DG and DH are negative but DS is positive.
(b) DG and DS are negative but DH is positive.
(c) DG is negative but DH and DS are positive.
(d) DG, DH and DS all are negative.
Answer. D

Question. In Freundlich adsorption isotherm, the value of 1/n is
(a) between 0 and 1 in all cases
(b) between 2 and 4 in all cases
(c) 1 in case of physical absorption
(d) 1 in case of chemisorption. 
Answer. A

Question. If x is amount of adsorbate and m is amount of adsorbent, which of the following relations is not related to adsorption process?
(a) x/m = f (p) at constant T
(b) x/m = f (T) at constant p
(c) p = f (T) at constant (x/m)
(d) x/m = p ×T
Answer. D

Question. The Langmuir adsorption isotherm is deduced using the assumption
(a) the adsorption sites are equivalent in their ability to adsorb the particles
(b) the heat of adsorption varies with coverage
(c) the adsorbed molecules interact with each other
(d) the adsorption takes place in multilayers.
Answer. A

Question. A plot of log(x/m) versus log P for the adsorption of a gas on a solid gives a straight line with slope equal to
(a) log k
(b) –log k
(c) n
(d) 1/n 
Answer. D

Question. Which is not correct regarding the adsorption of a gas on surface of a solid?
(a) On increasing temperature adsorption increases continuously.
(b) Enthalpy and entropy change is negative.
(c) Adsorption is more for some specific substance.
(d) It is a reversible reaction. 
Answer. A

Question. Which one of the following statements is not correct?
(a) The value of equilibrium constant is changed in the presence of a catalyst in the reaction at equilibrium.
(b) Enzymes catalyse mainly biochemical reactions.
(c) Coenzymes increase the catalytic activity of enzyme.
(d) Catalyst does not initiate any reaction.
Answer. A

Question. Which one of the following statements is incorrect about enzyme catalysis?
(a) Enzymes are mostly proteinous in nature.
(b) Enzyme action is specific.
(c) Enzymes are denatured by ultraviolet rays and at high temperature.
(d) Enzymes are least reactive at optimum temperature. 
Answer. D

Question. The enzyme which hydrolyses triglycerides to fatty acids and glycerol is called
(a) maltase
(b) lipase
(c) zymase
(d) pepsin.
Answer. B

Question. According to the adsorption theory of catalysis, the speed of the reaction increases because
(a) the concentration of reactant molecules at the active centres of the catalyst becomes high due to adsorption
(b) in the process of adsorption, the activation energy of the molecules becomes large
(c) adsorption produces heat which increases the speed of the reaction
(d) adsorption lowers the activation energy of the reaction. 
Answer. D

Question. A colloidal system has particles of which of the following size?
(a) 10^–9 m to 10^–12 m
(b) 10^–6 m to 10^–9 m
(c) 10^–4 m to 10^–10 m
(d) 10^–5 m to 10^–7 m
Answer. B

Question. Measuring zeta potential is useful in determining which property of colloidal solution?
(a) Viscosity
(b) Solubility
(c) Stability of the colloidal particles
(d) Size of the colloidal particles
Answer. C

Question. Which mixture of the solutions will lead to the formation of negatively charged colloidal [AgI]I– sol ?
(a) 50 mL of 0.1 M AgNO₃ + 50 mL of 0.1 M KI
(b) 50 mL of 1 M AgNO₃ + 50 mL of 1.5 M KI
(c) 50 mL of 1 M AgNO₃ + 50 mL of 2 M KI
(d) 50 mL of 2 M AgNO₃ + 50 mL of 1.5 M KI
Answer. B

Question. On which of the following properties does the coagulating power of an ion depend?
(a) The magnitude of the charge on the ion alone
(b) Size of the ion alone
(c) Both magnitude and sign of the charge on the ion
(d) The sign of charge on the ion alone
Answer. C

Question. The coagulation values in millimoles per litre of the electrolytes used for the coagulation of As₂S₃ are given below :
I. (NaCl) = 52, II. (BaCl₂) = 0.69,
III. (MgSO₄) = 0.22
The correct order of their coagulating power is
(a) I > II > III
(b) II > I > III
(c) III > II > I
(d) III > I > II
Answer. C

Question. Fog is a colloidal solution of
(a) solid in gas
(b) gas in gas
(c) liquid in gas
(d) gas in liquid.
Answer. C

Question. Which property of colloidal solution is independent of charge on the colloidal particles?
(a) Electroosmosis
(b) Tyndall effect
(c) Coagulation
(d) Electrophoresis
Answer. B

Question. The protecting power of lyophilic colloidal sol is expressed in terms of
(a) coagulation value
(b) gold number
(c) critical micelle concentration
(d) oxidation number.
Answer. B

Question. Which one of the following forms micelles in aqueous solution above certain concentration?
(a) Dodecyl trimethyl ammonium chloride
(b) Glucose
(c) Urea
(d) Pyridinium chloride 
Answer. A

Question. Position of non-polar and polar part in micelle
(a) polar at outer surface but non-polar at inner surface
(b) polar at inner surface non-polar at outer surface
(c) distributed over all the surface
(d) are present in the surface only. 
Answer. A

Question. Which one of the following method is commonly used method for destruction of colloid?
(a) Dialysis
(b) Condensation
(c) Filteration by animal membrane
(d) By adding electrolyte 
Answer. D

Question. At the critical micelle concentration (CMC) the surfactant molecules
(a) associate
(b) dissociate
(c) decompose
(d) become completely soluble
Answer. A

Question. The ability of anion, to bring about coagulation of a given colloid, depends upon
(a) magnitude of the charge
(b) both magnitude and charge
(c) its charge only
(d) sign of the charge alone. 
Answer. B

Question. When a few typical solutes are separated by a particular selective membrane such as protein particles, blood corpuscles, this process is called
(a) transpiration
(b) endosmosis
(c) dialysis
(d) diffusion.
Answer. C

Very Short Answer

Question. What are poisons? 
Answer. Poisons are substances that decrease the activity of a catalyst.

Question. What are promoters? 
Answer. Promoters are substances that enhance the activity of a catalyst.

Question. Why zeolites are good shape selective catalysis? 
Answer. Zeolites are good shape selective catalysts because of their honeycomb like structures.

Question. What are shape selective catalysis? 
Answer. The catalytic reaction that depends upon the pore structure of the catalyst and the size of the reactant and product molecules.

Question. Who made the systematic study of the effect of various foreign substances on the rates of chemical reactions? 
Answer. Berzelius made the systematic study of the effect of various foreign substances on the rates of chemical reactions

Short Answer

Question. What are the important features of solid catalysts? 
Answer. The two important features of solid catalysts are:
1. Activity: the activity of a catalyst depends upon the strength of chemisorption to a large extent. The reactants must get adsorbed reasonably strongly on to the catalyst to become active.
2. Selectivity: The selectivity of a catalyst is its ability to direct a reaction to yield a particular product selectively, when under the same reaction conditions many products are possible.

Question. What do you understand by the catalysis? 
Answer. The process by which a substance speeds up a chemical reaction without being consumed or altered in the process. The SI unit for catalysis is the katal. This is a derived
unit which is moles per second. When enzymes catalyse a reaction, the preferred unit is the enzyme unit

Question. How do zeolites work as catalyst? 
Answer. The zeolites trap the calcium and magnesium ions and release sodium ions in their place,so the water becomes softer but richer in sodium. Many everyday laundry and dishwasher detergents contain zeolites to remove calcium and magnesium and soften water so they work more effectively.

Question. What do you mean by mechanism of enzyme catalysis? 
Answer. The mechanism of enzyme catalysis. In order for a reaction to occur, reactant molecules must contain sufficient energy to cross a potential energy barrier, the activation energy.The lower the potential energy barrier to reaction, the more reactants have sufficient energy and, hence, the faster the reaction will occur.

Question. What do you mean by enzyme catalysts?? 
Answer. Enzyme catalysis is the increase in the rate of a process by a biological molecule, an enzyme. Most enzymes are proteins, and most such processes are chemical reactions.Within the enzyme, generally catalysis occurs at a localized site, called the active site

Long Answer

Question. Explain homogeneous catalysis? 
Answer. Homogeneous catalysis refers to reactions where the catalyst is in the same phase as the reactants, principally in solution. In contrast, heterogeneous catalysis describes processes where the catalysts and substrate are in distinct phases, typically solid-gas, respectively. Hydrogen addition to multiple bonds is catalysed by certain complex metal salts in solution. This may be described as homogeneous catalysis and, compared to heterogeneous catalysis, is a relatively new development in the area of the hydrogenation reactions. Acid catalysis, organometallic catalysis, and enzymatic catalysis are examples of homogeneous catalysis. Most often, homogeneous catalysis involves the introduction of an aqueous phase catalyst into an aqueous solution of reactants. Oxidation of sulphur dioxide into sulphur trioxide with the dioxygen in the presence of the oxides of the nitrogen as the catalyst chamber process. The reactants of sulphur di oxide and oxygen and the catalyst nitric oxide are all in the phase.

Question. What are the five steps mechanisms involves in modern adsorption theory? 
Answer. The five steps mechanisms involves in modern adsorption theory are:
1. Diffusion of reactants to the surface of the catalyst.
2. Adsorption of reactant molecules on the surface of the catalyst.
3. Occurrence of chemical reaction on the catalysts surface through the formation of an intermediate.
4. Desorption of the reaction products from the catalyst surface and thereby making the surface available again for more reaction to occur.
5. Diffusion of the reaction products away from the catalyst’s surface.
6. The surface of the catalyst unlike the inner part of the bulk has free valances which provide the seat for the chemical forces of the attraction.
7. When a gas comes in contact with such a surface its molecules are adsorbed side by side they may react with each other resulting in the formation of new molecules.

Question. Explain some of the applications of adsorption?
Answer. The applications of adsorption are:
1. Production of high vacuum, the remaining traces of air can be adsorbed by the charcoal from a vessel evacuated by a vacuum pump to give a very high vacuum.
2. Control of humidity, silica and aluminium gels are used as adsorbents for removing moisture and controlling the humidity.
3. In curing the diseases, a number of the drugs are used to kill the germs by getting adsorbed on them.
4. Gas mask is usually used for breathing in coal mines to adsorb poisonous gases.
5. Chromatographic analysis based on the phenomenon of adsorption finds a number of applications in analytical and industrial fields.
6. Removal of colouring natter from solutions, animal charcoal removes colours of solutions by adsorbing coloured impurities.

Question. Explain heterogeneous catalysis? 
Answer. Heterogeneous catalysts are catalysts that are in a different phase than the reactants. Heterogeneous catalysts are solids that are added into gas or liquid reaction mixtures. In heterogeneous catalysis, the reactants adsorb onto binding sites on the surface of the catalyst, and the availability of these reaction sites can limit the rate of the heterogeneous reactions. Heterogeneous catalysis is very important because it enables faster, large-scale production and the selective product formation. The production of 90% of chemicals (by volume) is assisted by solid catalysts. The chemical and energy industries rely heavily on heterogeneous catalysis. Oxidation of the sulphur dioxide into sulphur tri oxide in the presence of Pt., the reaction is in gaseous state while the catalyst is in the solid state.

Question. What are the characteristics of the enzyme catalysts?
Answer. The characteristics of the enzyme catalysts are:
1. Each enzyme is specific for a given reaction, i.e. one catalyst cannot catalyse more than one reaction.
2. One molecule of an enzyme may transform one million molecules of the reactant per minute.
3. The rate of an enzyme catalysed reaction is maximum at a particular pH, which is between pH values 5-7.
4. The enzyme activity is increased in the presence of the certain substances known as co-enzymes.
5. The rate of an enzyme reaction become maximum at a definite temperature called the optimum temperature’s
6. The inhibitors or poisons interacts with the active functional groups on the enzyme surface and often reduce or completely destroy the catalytic activity of the enzymes.

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