NEET UG Chemistry Surface Chemistry MCQs

Important Points

ˆ The study of chemistry regarding the boundary separating two bulk states or phases is called surface chemistry. This boundary surface is known as interface. It is expressed as hyphen (–) or slash (/). Dissolution, crystallization, catalysis, metallic corrosion are surface phenomena.

 ˆ The surface should be completely pure which can be obtained by vacuum generating method and can be stored also.

ˆ In this unit, surface phenomena like adsorption, catalysis, colloid and emulsion are studied.

ˆ In adsorption, the substance which is in solid form and on which other gas or liquid is adsorbed is called adsorbent. The substance that is adsorbed is called adsorbate and the whole phenomenon is called adsorption. The phenomenon opposite to adsorption is called desorption.

ˆ Absorption is such a phenomenon in which there is homogeneous system viz. any coloured solution but if solid adsorbent like charcoal is added to it then there is decrease in intensity of the colour which is adsorption. The combined phenomenon of adsorption and absorption is called sorption. In adsorption the concentration of adsorbate is more than that in the bulk. More porous the adsorbent more will be adsorption. Adsorption is an exothermic phenomenon.

ˆ In adsorption, the residual particles on the surface are responsible for the adsorption that is due to difference in forces of attraction.

ˆ Adsorption is of two types– Physical and Chemical. The points of difference between them are given in the unit.

ˆ Adsorption is used in many fields as well as in everyday life viz. To wear gas mask in which there is adsorbent to save from the poisonous gas like chlorine. Silica gel is used as adsorbent for keeping the electronic instruments moisture free. In the removal of yellow colour from sugar, the phenomenon of adsorption is used.

ˆ The factors affecting adsorption are (1) nature of adsorbate (2) nature of adsorbent (3) specific area of adsorbent surface (4) pressure of adsorbed gas (5) temperature. The detailed discussion about each one is included in the unit.

ˆ The study of Freundlich isotherm can be understood by the study of demonstration experiment in practicals book. There are many uses of adsorption which are described in the unit.

ˆ Catalysis is also a surface phenomenon. Some chemical reactions are slow. To increase their rates, the substance used in small proportion is called catalyst. This phenomenon is called catalysis. The catalyst is obtained back in original form at the end of the reaction.

ˆ There are two types of catalysis (1) Homogeneous and (2) Heterogeneous. In homogeneous catalysis, catalyst and the reactant are in one phase e.g. hydrolysis of methyl acetate in presence of H⁺ (2) In heterogeneous catalysis the catalyst and the reactants are in different phases e.g. Production of sulphuric acid in presence of V₂O₅ by contact process. There are many uses of homogeneous and heterogeneous catalysis as shown in the unit.

ˆ The characteristics of catalysis are activity, selectivity that is specific reaction; selection of specific catalyst e.g. zeolite. The zeolite named ZSM-5 is used to obtain gasoline from alcohol. Catalyst increases the rate of reaction but does not affect the equilibrium because it affects equally both the forward and the reverse reaction. Hence, more product is not obtained. ˆ Enzymes are proteins and are necessary for biochemical reaction. For every reaction separate and specific enzyme works viz. invertase can transform sugar into glucose and fructose. Urease can decompose urea into ammonia and carbon dioxide.

ˆ For enzyme catalysis the lock and key model or induced fit model are proposed. As the lock can be opened by suitable key, similarly for a particular reaction suitable enzyme will be required. The enzymes work at the temperature of the body i.e. 298-310 K temperature is considered the best.

ˆ Colloid chemistry is also a surface phenomenon. The colloidal solution is called sol. There are two components called dispersing phase and dispersion medium in it. The particles are of some particular size so this is a heterogeneous system. Colloids are of two types-Lyophilic and Lyophobic. The colloid which has attraction for solvent (dispersion medium) is used called lyophilic colloid e.g. gum. The colloid which has repulsion towards the solvent (dispersion medium is called lyophobic colloid. If water is as a medium then they are respectively called hydrophilic and hydrophobic. Colloids are of eight types which depend on the dispersing phase and dispersion medium. This is shown in the unit. Multimolecular, macromolecular and associated colloids are also known. In associated colloids molecules come nearer and form an association which is called micelle.

ˆ The certain temperature, at which the micelle is formed is called Kraft's temperature (TK). Below the critical micelle concentration (CMC), it remains in colloidal state and at higher than that concentration it is changed to solid in the form of precipitates. The formation micelle is obtained in the cleansing action of soap. Molecules like soap are shown as RCOONa, and their ionization form will be RCOO^–Na⁺. From this RCOO^–, R part combines with organic impurity and drags inside. It is called tail. The upper charged part COO^– attracts dust etc. and removes the dirt. It is called head.

ˆ The methods of preparation of colloids are as follows :

M.C.Q.

 

Question. Which of the following statements about chemisorption is not applicable?
(A) It involves chemical forces between adsorbent and absorbate
(B) It is irreversible in nature
(C) It involves high heat of adsorption
(D) It does not require activation energy
Answer : D

Question. A catalyst increases rate of reaction by :
(A) Decreasing enthalpy
(B) Decreasing internal energy
(C) Decreasing activation energy
(D) Increasing activation energy
Answer : C

Question. Some type of gels like gelatin loose water slowly. The process is known as :
(A) Synerisis
(B) Thixotropy
(C) Peptisation
(D) Imbibition
Answer : A

Question. Gold number of a lyophilic sol is such property that:
(A) the larger its value, the greater is the peptising power
(B) the lower its value, the greater is the peptising power
(C) the lower its value, the greater is the protecting power
(D) the larger its value, the greater is the protecting power
Answer : C

Question. Small liquid droplets dispersd in another liquid is called :
(A) Suspension
(B) Emulsion
(C) Gel
(D) True solution
Answer : B

Question. Protective sols are:
(A) lyophilic
(B) lyophobic
(C) both (A) and (B)
(D) none of (A) and (B)
Answer : A

Question. For the coagulation of 200 mL of As2S3 solution, 10 mL of 1 M NaCl is required. What is the coagulating value (number of milli moles of solute needed for coagulation of 1 liter of solution) of NaCl.
(A) 200
(B) 100
(C) 50
(D) 25
Answer : C

Question. Which of the following factors affects the adsorption of a gas on solid?
(A) Tc(critical temp.)
(B) Temperature of gas
(C) Pressure of gas
(D) All of them
Answer : D

Question. Colloidal solution of gold prepared by different methods of different colours because of :
(A) different diameters of colloidal gold particles
(B) variable valency of gold
(C) different concentration of gold particles
(D) impurities produced by different methods
Answer : A

Question. Volume of N₂ at NTP required to form a mono layer on the surface of iron catalyst is 8.15 ml/gram of the adsorbent. What will be the surface area of the adsorbent per gm if each nitrogen molecule occupies 16 × 10^–22 m².
(A) 16 × 10^–16 cm²
(B) 0.35 m²/g
(C) 39 m²/g
(D) 22400 cm²
Answer : B

Question. Which of the following ions is most effective in the coagulation of ferric hydroxide solution ?
(A) Cl¯
(B) Br–
(C) NO₂¯
(D) SO₄^2–
Answer : D

Question. All colloids
(A) are suspensions of one phase in another
(B) are two-phase systems
(C) contain only water-soluble particles
(D) are true solutions
Answer : B

 

 

(1) On which factors interface depends ?

(a) Size of the molecules in the bulk phase.

(b) Wieght of the molecules in the bulk phase.

(c) Numbers of molucules in the bulk phase.

(d) Physical state of molucules in the bulk phase.

 

(2) Which of the following phenomenon in not involved in surface chemistry ?

(a) Elecrode reactions (b) Dissolution

(c) Heterogeneous catalysis (d) Liquid and its vapour taken in closed vessel.

 

(3) How much pascal high vacuum is required to achive completely pure surface of metal?

(a) 10^-8 to 10^-9 (b) 10^-8 to 10^-10 (c) 10^-6 to 10^-9 (d) 10^-8 to 10^-7

 

(4) Due to adsorption

(a) surface energy increases (b) surface energy becomes zero

(b) surface energy decreases (d) no change occurs in surface energy

 

(5) Which of the following processes is adsortion phenomenon ?

(a) Soakd of rayon clothes in coloured solution

(b) Contact between silicagel and vapour of water

(c) Contact between anhydrous CaCl₂ and vapour of water

(d) H₂S gas in contact to water.

 

(6) Which of the following is good adsorbent ?

(a) Silica gel (b) Alumina (c) Clay (d) All the given

 

(7) Which type of process adsorption is ?

(a) Isotonic (b) Isochonic (c) Indothermic (d) Exothermic

 

(8) When adsorption phenomenon occurs complete ?

(a) ΔH < O,ΔG < O,ΔS < O (b)ΔG < O,ΔH < O,ΔS > O

(c) ΔH > O,ΔS > O,ΔG < O (d)ΔG < O,ΔS < O,ΔH > O

 

(9) Which is correct for adsorption ?

(a) Δ H-T Δ S is negative (b) ΔH is positive

(C) Δ H-T Δ S is positive (d) TΔS and ΔG=0

 

(10) Which of the following statement is not true ?

(a) The value of adsorption enthalpy of physical adsorption is less than chemical adsorption.

(b) Physical adsorption occurs due to van der waals’ forces

(c) Chemical adsorption decreases at high temperacture and low pressure.

(d) Physical adsorption is reversible.

 

(11) At which temperature chemical adsorption occurs ?

(a) At high temperature (b) At very low temperature

(c) At low temperature (d) Temperature does not affect.

 

(12) Whose value is less than zero during adsoption ?

(a) DG (b)ΔH (c)ΔS (d)All the given

 

(13) How molecules of gases are deposited on the surface of solid during physical adsorption ?

(a) By electrostatic forces (b) By chemical forces

(c) By gravitational forces (d) By van der waals’ forces

 

(14) What is used to prevante electronic instruments clamaged by the moisture ?

(a) Silica gel (b) Zeolite

(c) Chromatographic plate (d) All the given

 

(15) On which factor adsorption of gas on solid adsorbtion depend ?

(a) On temprature (b) On pressure of gas

(c) On nature of adsorbent (d) All the given

 

 

(23) Which of the following is not true regarding to Freudlich adsorption isotherm ?

(a) This isotherm is applicable in certain limit of pressure

(b) Constant k and n change with temprature

(c) It shows deviation at low pressure

(d) Freundlich isotherm is empirical, there is no theoritical proof of it.

 

(30) In Indothermic reaction with the increase of temperature adsorption will be

(a) constsnt (b) increase (c) decrease (d) none of these

 

(31) Which adsorbent is used in separation of inert gases by Dewar’s method ?

(a) Vanadium pentoxide (b) Silica gel

(c) Activated charcoal (d) Allumina

 

(32) Which of the following are adsorption indicators ?

(a) eosin (b) fluorescin (c)methelene blue (d) (a) and (b)

 

(33) What is not true for catalytic reaction ?

(a) Catalyst increases equally both the rate of forward and reverse reactions.

(b) Catalyst does not effect to equilibrium constant.

(c) Catalyst decreases activation energy

(d) Catalyst increases activation energy of chemical equation.

 

(34) Which catalyst forms NH₃ and CO₂ from urea ?

(a) Invertase (b) Celluase (c) Urease (d) Pepcine

 

(35) Which of the following is an example of surface catalysis ?

(a) Inversion of sucrose

(b) Production of ammonia by Haber’s process

(c) Production of H₂SO₄  by lead chamber process

(d) Hydrolysis of ester

 

(36) Which catalyst is used in inversion of sucrose ?

(a) Fe_(s) (b) NO_(g) (c) H₂SO₄ (d) Cl_(g)

 

(37) Which catalyst is used to obtain methanal from water gas ?

(a) Cu (b) ZnO-Cr₂O₃ (c) (a) and (b) (d) FeO

 

 

 

(43) On which factor shape-selective catalysis depends ?

(a) Size of reactant malecules (b) Pore structure of catalyst

(c) Size of product molecules (d) All the given

 

(44) How many times reaction rate increase by catalyst ?

(a) 10¹⁰ to 10²⁰ (b) 10² to 10⁴

(c) 10⁶ to 10⁸ (d) 10⁸ to 10²⁰

 

(45) What is called colloid system in which dispesing phase and dispersion medium, both are in solid state ?

(a) Gel (b) Emulsion (c) Sol (d) Aerosol

 

(46) What is called colloid system in which dispersing phase is gas and dispersion medium is lquid ?

(a) Gel (b) Areosol (c) Emulsion (d) Foam

  

(47) Milk is example of which type of colloid ?

(a)Emulsion (b) Suspension (c) Gel (d)Aerosol

 

(48) Smoke is which type of colloidal system ?

(a) Gas in salid (b) Solid in gas (c) Gas in gas (d) Gas in liquid

 

(49) Which of the following is reversible sol ?

(a) Cellulose (b) (c) Mist (d) Gelatin

 

(50) Which type of sol sulphar is ?

(a) Multimolecular colloid (b) Micelle

(c) Associated colloid (d) Macromolecular colloid

 

(51) Which of the following is macromolecalar colloid ?

(a) Artificial rubber (b) Protein (c) Nylon (d) All the given

 

(52) What is called to that temperature at which the formation of micelle takes place ?

(a) Zero temperature (b) Kraff temperatue

(c) Kelvin temperature (d) Absolute temperature

 

(53) At which condition micelle is formed ?

(a) At concentration higher then critical micelle concentration and lower then kraft temperature.

(b) At concentration higher then critical micelle concentration and higher then kraft temperature.

(c) At concentration lower then critical micelle concentration and lower then kraft temperature.

(d) At concentration lower then critical micelle concentration and higher then kraft temperature.

 

 

(60) In which of the following method condensation and dispersion are associated ?

(a) Excessive cooling (b) Hydrolysis (c) Bredig’s are (d) Peptization

 

(61) Which method is is used to obtain sol of gold and silver ?

(a) Electric dispersion (b) Peptization (c) Excessive cooling (d) Mechanical dispersion

 

(62) Whose menbranes are used in dialysis ?

(a) Parchment paper (b) Plastic (c) Filter paper (d) Ultrafilter paper

 

(63) ___Phenomenon is called reverse to coagulation ?

(a) Flocculation (b) Tyndall (c) Brownian (d) Dialysis

 

(69) By the use of which colligative property molecularmass of colloid can be determine ?

(a) Decrease in vapour pressure (b) Elevation in boiling point

(c) Depression infeezing point (d) Osmotic pressure

 

(70) Which of the following is oil/water emulsion ?

(a) Milk (b)Vanishing cream (c) Butter (d) All the given

 

(71) Which of the following substance is used as stabilizer in emulsion ?

(a)Protein (b) Gum (c)Agar (d) All the given

 

(72) Tyndall effect is associated with which property of colloid ?

(a) Mechanical (b) Colligative (c) Optical (d) Electrical

 

(73) Which method is used for demulsification ?

(a) Sulimation (b) DIstillation (c) Filtration (d) Centrifugation

 

(74) Surface-tention of lyophobic sol is

(a) less then water (b) greater then water(c) equal to water (d) can not be predict

 

(75) for the preparation of which substances reversible micelle is used ?

(a) Medicines (b) Nano products (c) Rubber plating (d) All the given

 

(76) Tyndall effect is shown by

(a) Ideal solution (b) Colloidal solution (c) Saturated solution (d)True solution

 

(77) Which of the following can prepare cationic micelle ?

(a) Sodium stearate (b) Cetyltrimethyl ammonium bromide

(c) Urea (d) Sodium dodesylsulphate

 

(78) When the rate of physical adsorption will increase ?

(a) By reducing pressure (b) By reducing temperature

(c) By increasing temperature (d) (a) and (c)

 

(79) According to the adsorption theory of catalysis, the speed of the reaction increases because

(a) Adsorption produces heat which increases the speed of the reaction.

(b) Adsorption lowers the activation energy of the raction

(c) The concentration of reactant molecules at the active centres of the catalyst becomes high due to adsorption.

(d) In the process of adsorption, the activation energy of the molecules become large.

 

(80) Which of the following property is true ?

(a) The particles of colloid can diffuse slowly through semipermeable membrance

(b) The particles of colloid can not be settle down under the influence of gravitational force.

(c) The particle of colloid can not be observed by ultramicroscope.

(d) All the given.

 

(81) In a case of auto-catalysis

(a) reactant act as a catalyst (b) heat ivolved during reaction, act as a catalyst

(c) product act as a catalyst (d) solvant act as a catalyst

 

(82) When light passes through collodial solution it _____

(a) is reflected (b) is refracted (c) is scatterd (d) does not affect 

 

 

(83) Which of the following is least effective for flocculation >

(a) k₂ CrO₄ (b) KBr (c)  K₂SO₄  (d) K₃[Fe (CN)₆ ]

 

(84) 0.25g of starch sol is required to prevent coagulation of 10ml gold sol when 1 ml of 10% NaCl solution is present. What is gold number of starch sol ?

(a) 0.25 (b) 2.5 (c) 250 (d) 0.025

 

(85) Which of the following is appropriate ?

(a) Emulsion - butter milk (b) Aerosol - smoke

(c) Foam - fogs (d) Solid sol - cake

 

(86) Which of the following has minimum value of coagulation for AS₂S₃ ?

(a) Kcl (b) 2 Bacl (c) Nacl (d) AlCl₃

 

(87) Surface tention of lyophilic sol is

(a) greater than H₂O (b) equal to H₂O (c) less than H₂O (d) none of these

 

(88) Which of the following is an example of homogeneous catalysis ?

(a) Acidic hydrolysis of methyl acetate

(b) Catalytic coversion in methanol from watergas

(c) Catalytic coversion in SO₃ from SO₂ by contract process

(d) Synthesis of NH3 by Haber’s process

 

(89) In peptiration reaction

(a) colloid coverts in precipitates

(b) precipitates converts in calloid

(c) true solution is formed from suspention particels.

(d) true solution is formed by dissolving precipitates.

 

(90) From which of the following effect colloidal system is free ?

(a) gravitational (b) Concentration of electrolyte

(c) heat (d) applied electrical field.