SURFACE CHEMISTRY
MCQ type question
Q1 Which of the following statement is not correct regarding physical adsorption?
a.) it is not specific
b.) it forms monomolecular layers
c.) it has low heat of adsorption
d) it is reversible
Ans- b
Q 2. Which of the following is adsorbed by charcoal to maximum extent ?
a.) N2
b) CO2
c.) Cl2
d) O2
Ans- b
Q3. An example of micelle is
a) Sodium stearate
b) gold gel
c) solution of NaCl
d) Ruby glass
Ans - a
4. Alum helps in purifying water by
a) forming silicon complex with clay particles.
b) sulphate part which combines with dirt and removes it.
c) Aluminum which coagulates the mud particles.
d) making mud water soluble.
Ans-c
5 The disease kalaazar is caused by
a) colloidal antimony
b) milk of magnesia
c) argyrols
d)colloidal gold
Ans- a
6. Which one of the following is a property of physisorption?
(1) Non-specific nature
(2) High specificity
(3) Irreversibility
(4) Single layer adsorption
Answer (a) Physisorption is non-specific, reversible, multilayred.
7. Which of the following is not a characteristic of chemisorption?
(a) Irreversible nature
(b) Change in enthalpy is of the order of 500 J
(c) Specific in nature
(d) Increases with increase of surface area Sol.
Answer (b) ΔH of chemisorption is of the order of 80 – 240 kJ.
8. Freundlich adsorption isotherm gives a straight line on plotting
(a) x/m versus P
(b) log x/m versus P
(c) log x/m versus log P
(d) x/m versus 1/P
Answer (c)
9. The process of froth floatation and chromatography are based on
(a) Emulsification
(b) Adsorption
(c) Absorption
(d) Both (b) & (c)
Answer (b)
10. Which of the following is correct about the adsorption of N2 over Iron?
(a) It is always physically adsorbed
(b) Extent of adsorption over iron decreases with the increase in temperature first and then increases
(c) It is always chemically adsorbed
(d) N2 is never adsorbed over iron
Answer (b) Adsorption of N2 over iron is an example of chemisorption
11. Size of colloidal particle ranges between
(a) 1 nm to 100 nm
(b) 1 nm to 1000 nm
(c) 10 nm to 1000 nm
(d) 100 nm to 1000 nm
Answer (b)
12. Which is not a colloidal solution?
(a) Smoke
(b) Ink
(c) Air
(d) Blood
Answer (c) Air is homogenous mixture so not colloid solution.
13. Lyophobic colloids are
(a) Reversible colloids
(b) Irreversible colloids
(c) Protective colloids
(d) Gum, proteins
Answer (b) Irreversible colloids.
14. Which of the following processes best describes the purification of muddy water by addition of alum?
(a) Absorption
(b) Coagulation
(c) Dialysis
(d) Electrodialysis
Answer (b) Alum coagulates the impurities present in muddy water, which settles down.
15. Colloidal solution commonly used in treatment of eye disease is
(a) Colloidal sulphur
(b) Colloidal silver
(c) Colloidal gold
(d) Colloidal antimony
Answer (b) Colloidal silver = argyrol.
16. Micelles formation takes place
(a) At CMC and at kraft temperature
(b) At CMC and at above kraft temperature
(c) At above CMC and at kraft temperature
(d) Above CMC and above kraft temperature
Answer (d)
17. Which of the following is positively charged colloidal particle?
(a) As2S3
(c) Al2O3.xH2O
(3) Au
(d) Pt
Answer (2) Al2O3.xH2O [Generally, oxides are positively charged colloidal solution.]
18. Colloids can be purified by
(a) Tyndall effect
(b) Coagulation
(c) Peptization
(d) Ultrafiltration
Answer (d)
19. Which of the following has minimum protecting power? (out of 12 cbse syllabus)
(a) Gelatin (Gold no. = 0.01)
(b) Dextrin (Gold no. = 15)
(c) Potato starch (Gold no. = 25) (d) Albumin (Gold no. = 0.25)
Answer (c) Protecting power α 1/ Gold number
20. Movement of colloidal particles under the influence of electric field is called
(a) Electrophoresis
(c) Dialysis
(c) Ionisation
(b) Electrodialysis
Answer (a)
21. Emulsifier is an agent which
(a) Accelerates the dispersion
(b) Stabilizes the emulsion
(c) Homogenizes the emulsion
(d) Dissociate emulsions
Answer (b) Emulsifier stabilises the emulsion.
22. Gelatin is often used as an ingredient in the manufacture of ice-cream. The reason for this is
(a) To prevent the formation of a colloid
(b) To stabilize the colloid and prevent crystal growth
(c) To cause the mixture to solidify
(d) To improve the flavour
Answer (b)
23. Milk can be preserved by adding a few drops of
(a) Formic acid solution
(b) Formaldehyde solution
(c) Acetic acid solution
(d) Acetaldehyde solution
Answer (b)
24. When a river enters the sea, a delta is formed. Formation of delta is due to
(a) Peptization
(b) Coagulation
(c) Emulsification
(d) Dialysis
Answer (b) River water is a colloidal solution of clay and sea water contains a number of electrolytes. When river water meets the sea water, the electrolytes present in the sea water, coagulate the colloidal solution of clay which resulting in its deposition with formation of delta.
25. Which statement is incorrect?
(a) Higher the gold number of lyophilic sol better is its protective action
(b) Lower the gold number of a lyophilic sol better is its protective action
(d) The Bredig's arc method is usually suitable for preparing sols of inert metals
(d) The osmotic pressure method gives the average molar mass of a polymer
Answer (a) protective action α 1/Gold number
26. The potential difference between the fixed charged layer and the diffused layer having opposite charge is called
(a) Zeta potential
(b) Streaming potential
(c) Dorn potential
(d) Colloidal potential
Answer (a)
27. When dilute aqueous solution of AgNO3 (excess) is added to KI solution, positively charged sol particles of AgI are formed due to adsorption of ion
(a) K+
(b) Ag+
(c) I–
(d) NO3 –
Answer (b)
28. Colloidal particles in soap sol carry
(a) Negative charge
(b) Positive charge
(c) No charge
(d) Either positive or negative charge
Answer (a)
29. Which of the following metallic sols cannot be prepared by Breding’s arc method?
(a) Gold
(b) Silver
(c) Platinum
(d) Sodium
Answer (d)
30.The stabilization of the dispersed phase in a lyophobic sol is due to
(a) The viscosity of the medium
(b) The surface tension of the medium
(c) Affinity for the medium
(d) The formation of an electrical double layer between the two phases
Answer (d)
39. When FeCl3 solution is added to NaOH a negatively charged sol is obtained. It is due to the
(a) Presence of basic group
(b) Preferential adsorption of OH– ions
(c) Self dissociation
(d) Electron capture by sol particles
Answer (d) FeCl3 + NaOH ------> Fe2O3.xH2O/OH–
40. Which of the following is used to absorb water?
(a) Silica gel (b) Calcium acetate (c) Hair gel (d) Anhydrous CaCl2
Ans- d
41. The heat evolved in physisorption lies in the range (kJ/mol) of
(a) 20-40
(b) 40-100
(c) 100-200
(d) 200-400
Ans- a
42. Adsorbed acetic acid on activated carbon is
(a) Adsorber
(b) Absorber
(c) Adsorbent
(d) Adsorbate
Ans-c
43. The graph between log x/m versus log P is straight line inclined at an angle 45° with intercept 0.30. What will be rate of adsorption at pressure 0.4 atm.
(a) 0.4
(b) 0.6
(c) 0.8
(d) 0.9
Ans.-c
Solution- Slope in equation is 1/n = tan450 =1
Intercept is logk = 0.30, that implies k=2
Hence by equation m/x =kp1/n
k=2, n=1 and p=0.4
∴ Rate of adsorption, x/m is 0.8.
44. The nature of colloidal solution obtained when excess FeCl3 is added in precipitate of Fe (OH)3?
(a) (+) vely charged
(b) (–) vely charged
(c) No charge
(d) All of above
Ans- a
fill in the blanks
45.At high concentration of soap in water, soap behaves as------.
Ans- associated
46 The lyophobic colloid is protected by -----------from electrolytes
Ans - adding of lyophilic colloids
47.The term sorption stands for-----------.
Ans- both adsorption and absorption
48.The physical adsorption of gases may change to chemical adsorption with------
Ans- on increasing temperature
49.At equilibrium position in the process of adsorption delta H is ------------.
Ans-∆H = T∆S
at equilibrium, rate of forward reaction = rate of backward reaction. so this reason, there is no work done by the system. and hence Gibbs free energy equals to zero.
Assertion- Reason Type Questions
The question given below consist of an assertion and reason. Use the following key tochoose appropriate answer
a) If both assertion and reason are correct and reason is correct explanation of the 19 assertion
b) if both assertion and reason are correct but reason is not the correct explanation of the assertion.
c) If assertion is correct but reason is incorrect.
d) if assertion is incorrect but reason is correct.
e) if both assertion and reason both are incorrect.
1. Assertion: physical adsorption of molecules on the surface requires activation energy.
Reason: because the bonds of adsorbed molecules are broken.
Ans - e
2 Assertion: activity of enzymes is pH dependent.
Reason: change of PH affects the solubility of the enzyme in water.
Ans-b
3 Assertion: small quantity of soap is required to prepare a stable emulsion.
Reason: Soaps lower the interfacial between the oil and water.
Ans- a
4 ASSERTION: sea water looks blue.
Reason: due to scattering of light by colloidal particles in sea water.
Ans-a
5 Assertion: the conversion of fresh precipitate to colloidal state is called peptization.
Reason: it is caused by addition of common ions.
Ans- b
TWO MARKS QUESTIONSQ
1.What is adsorption isotherm? Describe Freundlich adsorption isotherm at intermediate pressure.
2. Define:-
a) zeta potential
b) CMC.
3. Out of BaCl2 and KCl which is more effective in causing coagulation of negatively charged sol. give reason.
4. What happens when dialysis is prolonged?
5. What is collodion?
THREE MARKS QUESTIONS
1.Explain the following observations
a) Ferric hydroxide sol gets coagulated on addition of sodium chloride solution.
b) Cottrell's smoke precipitator is fitted at the mouth of chimney us
2. what are the differences between multimolecular, macromolecular and associated colloids?
3. what happens when—
a) a freshly prepared precipitate of Fe (OH)3 is shaken with small amount of FeCl3 solution.
b) electric current is passed through colloidal sol.
c)an emulsion is centrifuged.
4. Define
a) Micelles
b) Peptization
c) desorption.
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