Surface Chemistry VBQs Class 12 Chemistry

VBQs Surface Chemistry Class 12 Chemistry with Surface Chemistry has been provided below for standard students. We have provided chapter wise VBQ for Class 12 Chemistry with Surface Chemistry. The following Surface Chemistry Class 12 Chemistry value based questions with answers will come in your exams. Students should understand the concepts and learn the solved cased based VBQs provided below. This will help you to get better marks in class 12 examinations.

Surface Chemistry VBQs Class 12 Chemistry

Assertion & Reasoning Based MCQs

For questionS, a statement of assertion followed by a statement of reason is given. Choose the correct answer out of the following choices.
(a) Assertion and reason both are correct statements and reason is correct explanation for assertion.
(b) Assertion and reason both are correct statements but reason is not correct explanation for assertion.
(c) Assertion is correct statement but reason is wrong statement.
(d) Assertion is wrong statement but reason is correct statement.

Question. Assertion : The molecules on the surface have lesser energy than the molecules inside.
Reason : During adsorption, the surface of solid is in a state of strain.

80. Assertion : A colloidal sol scatters light but a true solution does not.
Reason : The particles in a colloidal sol move slowly than in a true solution.

Question. Assertion : Muddy water is an example of sol.
Reason : A colloidal system in which solid is dispersed in a liquid is called sol.

Question. Assertion : There is no interface between gases.
Reason : The shape and volume of gases are not definite.

Question. Assertion : Lyophilic colloids are called reversible sols. 
Reason : Lyophilic sols are liquid loving.

Question. Assertion : Colloidal particles show Brownian movement. 
Reason : Brownian movement arises because of the impact of the molecules of the dispersion medium with the colloidal particles.

Question. Assertion : A colloidal sol of As₂S₃ is coagulated faster by 0.1 M BaCl₂ than by 0.1 M NaCl. 
Reason : BaCl₂ gives double the number of Cl^– ions than NaCl.

Question. Assertion : Gold number is a measure of protective action by a lyophilic colloid on a lyophobic colloid.
Reason : Zeta potential (or electrokinetic potential) is the potential difference between fixed charged layer and the diffused layer having opposite charge.

Question. Assertion : Porous or finely divided forms of adsorbents adsorb larger quantities of adsorbate. 
Reason : The greater the surface area of the solid, the greater would be its adsorbing capacity.

Question. Assertion : According to Freundlich, x/m = k.P^1/n
Reason : The isotherm shows variation of the amount of gas adsorbed by the adsorbent with temperature.

Question. Assertion : Soap and detergent are macromolecular colloids.
Reason : Macromolecular colloids are formed by molecules of large size.

Question. Assertion : When FeCl₃ is added to an excess of hot water, a positively charged sol of hydrated ferric oxide is formed. 
Reason : When ferric chloride is added to NaOH solution a negatively charged sol is obtained due to adsorption of OH^– ions.

Question. Assertion : NH₃ is adsorbed more readily than O₂ on charcoal.
Reason : More easily liquefiable gases are adsorbed easily.

Short Answer Type Questions-I

Question. (i) Why is Chemisorption referred to as activated adsorption?
(ii) What type of colloid is formed when a liquid is dispersed and a solid is in dispersion? Give an example. 
Answer. (i) Chemisorption involves formation of bonds between the solid surface (adsorbent) and gaseous atoms/molecules (adsorbate). Since formation of chemical bonds requires high activation energy, it is known as activated adsorption.
(ii) Gel is a colloidal solution in which liquid is dispersed in a solid dispersion medium. Example- Cheese / butter.

Question. What do you understand by an adsorption isotherm? Give a brief description of Freundlich’s isotherm. 
Answer. A graph drawn between extent of adsorption of gas on the adsorbent and the pressure of the gas at constant temperature is called adsorption isotherm.
An empirical relationship between the amount of gas adsorbed by unit mass of solid adsorbent (x/m) and the equilibrium pressure (p) can be given by

where, n is a positive integer and k is the constant.
Taking log both the sides,

Question. Write one difference in each of the following:
(a) Multimolecular colloid and associated colloid
(b) Coagulation and peptization
Answer.

Question. Define the following terms:
(i) Protective colloid
(ii) Zeta potential 
Answer. (i) Protective colloid: The process by which the lyophobic sols are protected from coagulation by electrolytes due to the previous addition of a lyophilic colloid is called protection and the colloids are called Protective colloids.
(ii) Zeta potential: It is the potential difference between the dispersion medium and the stationary layer of fluid attached to the dispersed particle.

Question. (i) How does the precipitation of colloidal smoke take place in Cottrell precipitator?
(ii) Freundlich adsorption isotherm is given by the expression x/m = kp^1/n What conclusions can be drawn from this expression? 
Answer. (i) In Cottrell precipitator, charged smoke particles are passed through a chamber containing plates with charge opposite to the smoke particles. Smoke particles lose their charge on coming in contact to the plates and get precipitated. Hence, particles settle down on the floor of the chamber.
(ii) Following conclusions can be drawn from the equation:
(a) When 1/ n = 0, the adsorption is independent of pressure.
(b) When n = 1, x/m vs p graph is a straight line with slope 1. This show x/m ∝ p, means adsorption is dependent upon the pressure directly.

Question. (i) Define adsorption with an example.
(ii) Write one similarity between Physiorption and Chemisorption. 
Answer. (i) The phenomenon of accumulation of higher concentration of the molecular species on the surface of the solid than in the bulk is called adsorption. e.g. Activated charcoal adsorbs a number of gases like ammonia, phosgene etc.
(ii) Both are surface phenomenon / both increase with increase in surface area (or any other correct similarity).

Question. Explain the following:
(i) Same substance can act both as colloids and crystalloids.
(ii) Artificial rain is caused by spraying salt over clouds.
Answer. (i) The nature of the substance whether colloid or crystalloid depends upon size of the solute particles. When the size of solute particles lies between 1 nm to 1000 nm, it behaves as a colloid. Whereas size of particles is less than 1 nm, it behaves as crystalloids.
(ii) The colloidal particles of the clouds that carry charges, get neutralized and coagulated to bigger water drops by spraying salt over clouds and as a result artificial rain is occurred.

Question. Give reasons for the following observations:
(i) Leather gets hardened after tanning.
(ii) Lyophilic sol is more stable than Lyophobic sol.
Answer. (i) Mutual coagulation. 
(ii) Strong interaction between dispersed phase and Dispersion medium or solvated layer.

Question. With the help of an example, explain how physisorption changes to chemisorption with rise in temperature? Give the reason for the change.
Answer. Adsorption of hydrogen gas on finely divided nickel is physisorption at low temperatures as it involves weak Van der Waals forces. With the rise in temperature, hydrogen molecules dissociate to form hydrogen atoms which are held on the surface by chemisorption.

Question. Write the main reason for the stability of colloidal sols. 
Answer. The colloidal particles carry same charge which can be either positive charge or negative charge.
The similar charged colloidal particles repel each other. This prevents from aggregating when these particles come closer to each other.

Question. Write one difference between each of the following:
(i) Multimolecular colloid and Macromolecular colloid
(ii) Sol and Gel 
Answer.

Question. Define Brownian movement. What is the cause of Brownian movement in colloidal particles? How is it responsible for the stability of Colloidal sol?
Answer. Brownian movement: The particles of the dispersed phase of colloidal solution execute a continuous zigzag motion. This phenomenon is called Brownian movement.
Cause of Brownian movement: The dispersed phase particles of the colloidal solution are constantly collided by the molecules of the dispersion medium.
Brownian movement opposes the force of gravity on the colloidal particles. So, these particles always remain in a state of motion and do not settle.

Question. Write one difference in each of the following:
(i) Lyophobic sol and Lyophilic sol
(ii) Solution and Colloid
Answer. (i) Lyophobic sols are liquid (dispersion medium)- hating and lyophillic sols are liquid (dispersion medium)-loving colloids.
(ii) Solution is a homogeneous mixture while colloid is heterogeneous mixture/does not show Tyndall effect.

Question. (i) Why are medicines more effective in colloidal state?
(ii) What is the difference between an emulsion and a gel?
Answer. (i) Due to large surface area these are easily assimilated or adsorbed.
(ii) Emulsion – Both dispersed phase and dispersion medium are liquid. Example – Milk. Gel- Dispersed phase is liquid while Dispersion
medium is solid. Example – Butter.

Question. (i) Write the expression for Freundlich’s equation to describe the behaviour of adsorption from solution phase.
(ii) What causes charge on sol particles?
Answer. (i)
Frendlich adsorption isotherm, x/m = kC^1/n 
Where, x/m = quantity of gas adsorbed in unit mass of solid adsorbent
C = equilibrium concentration
k, n = constants at a given temperature
(ii) The charge on the sol particles is due to:
(a) Electron capture by sol particles during electrodispersion.
(b) Preferential adsorption of ions from solution.
(c) Formulation of electrical double layer.

Question. Define the following terms:
(i) Desorption
(ii) Critical Micelle Concentration 
Answer. (i) The process of removing an adsorbed substance from a surface on which it is adsorbed. 
(ii) The formation of micelles takes place only above a particular concentration called CMC.

Short Answer Type Questions-II

Question. (a) Write the dispersed phase and dispersion medium of milk.
(b) Write one similarity between physisorption and chemisorption.
(c) Write the chemical method by which Fe(OH)₃ sol is prepared from FeCl₃.
Answer. (a) Dispersed phase-liquid and Dispersion medium-liquid. 
(b) Both are surface phenomena/both increase with increase in surface area (or any other correct similarity) 
(c) Hydrolysis,

Question. (a) Write the dispersed phase and Dispersion medium of butter.
(b) Why does physisorption decrease with increase in temperature?
(c) A colloidal sol is prepared by the method given in the figure. What is the charge on AgI colloidal particles formed in the test tube?
How is this sol represented?

Answer. (a) Dispersed phase = Liquid
Dispersion medium = Solid/liquid 
(b) Because physisorption is exothermic in nature and with rise in temperature, desorption starts.
(c) Negatively charged , AgI/I^–

Question. (i) What is the role of activated charcoal in gas mask?
(ii) A colloidal sol is prepared by the given method in figure. What is the charge on hydrated Ferric Oxide colloidal particles formed in the test tube?
How is the sol represented?

(iii) How does Chemisorption vary with temperature?
Answer. (i) Adsorption of toxic gases. 
(ii) Negative charge ; Fe₂O₃.xH₂O/OH^– 
(iii) Increases with increase in temperature/ First increases then decreases.

Question. (a) Write the dispersed phase and dispersion medium of dust.
(b) Why does Physisorption reversible whereas Chemisorption is irreversible?
(c) A colloidal sol is prepared by the method given in the figure. What is the charge on AgI colloidal particles formed in the test tube?
How is this sol represented?

Answer. (a) Dispersed phase = Liquid; Dispersion medium = Gas 
(b) Due to weak Van der Waal’s forces in physisorption whereas strong chemical forces in chemisorption. 
(c) Positively charged , AgI/Ag⁺

Question. Write any three differences between Physisorption and Chemisorption.
OR
Write three differences between Physisorption and Chemisorption. 
Answer. 

Question. Give reason for the following observations:
(i) When silver nitrate solution is added to Potassium Iodide solution, a negatively charged colloidal solution is formed.
(ii) Finely divided substance is more effective as an adsorbent.
(iii) Lyophilic colloids are also called reversible sols.
Answer. (i) The precipitated Silver Iodide adsorbs Iodide ions from the Dispersion medium resulting in the negatively charged colloidal solution. 
(ii) Due to large surface area.
(iii) If the dispersion medium is separated from the dispersed phase, the sol can be reconstituted by simply remixing with the dispersion medium. That is why, these sols are also called
reversible sols. 

Question. (i) Differentiate between Adsorption and Absorption.
(ii) Out of MgCl₂ and AlCl₃, which one is more effective in causing coagulation of negatively charged sol and why ?
(iii) Out of sulphur sol and proteins, which one forms multimolecular colloids ?

Answer. (i)

(ii) AlCl₃ is more effective in causing coagulation of negatively charged sol because according to Hardy and Schulze rule, greater the valency of the flocculating ion, greater is its ability to bring coagulation. 
(iii) Sulphur sol forms multimolecular colloids.

Question. Answer the following questions:
(a) Which of the following electrolytes is most effective for the coagulation of AgI/Ag+ sol?
MgCl₂, K₂SO4, K₄[Fe(CN)₆]
(b) What happens when a freshly precipitated Fe(OH)3 is shaken with a little amount of dilute solution of FeCl3?
(c) Out of Sulphur sol and Proteins, which one forms Macromolecular colloids?
Answer. (a) K4[Fe(CN)₆] 
(b) Fe(OH)₃ is converted into colloidal state by preferential adsorption of Fe3+ ions.
(c) Proteins

Question. Explain the following phenomenon giving reasons:
(i) Chemical adsorption increases with increase in temperature.
(ii) Alum is applied on a cut to stop bleeding.
(iii) Sky appears blue in colour.
Answer. (i) High energy of activation is needed. 
(ii) Blood being a colloidal solution, gets coagulated by alum (an electrolyte). 
(iii) Dust particles along with water suspended in air scatter blue light which reaches our eyes.

Question. (a) Write the dispersed phase and dispersion medium of milk.
(b) Why is adsorption exothermic in nature?
(c) Write Freundlich adsorption isotherm for gases at high pressure.
Answer. (a) Dispersed phase = liquid
Dispersion medium = liquid
(b) Due to the formation of new bonds / force of attraction between adsorbate and adsorbent
(c) x/m = kp° = k

Question. Write three differences between lyophobic sol and lyophilic sol. 
Answer. Differences between lyophobic and lyophilic sol:

Question. What happens when
(a) a freshly prepared precipitate of Fe(OH)₃ is shaken with a small amount of FeCl₃ solution ?
(b) persistent dialysis of a colloidal solution is carried out ?
(c) an emulsion is centrifuged ?
Answer. (a) Peptization occurs / Colloidal solution of Fe(OH)₃ is formed. 
(b) Coagulation occurs. 
(c) Demulsification or breaks into constituent liquids.

Question. Answer the following questions:
(i) What happens when a freshly precipitated Fe(OH)₃ is shaken with a little amount of dilute solution of FeCl₃ ?
(ii) Why are lyophilic colloidal sols more stable than lyophobic colloidal sols ?
(iii) What form Freundlich adsorption equation will take at high pressure ? 
Answer. (i) A reddish brown coloured colloidal solution is obtained.
(ii) Stability of lyophilic sols is due to:
(a) same charge on all the colloidal particles.
(b) solvation of the colloidal particles.
(iii) At high pressure amount of gas adsorbed (x/m) becomes independent of pressure (p).

Freundlich isotherm fails at high pressure, because rate of adsorptions saturates at high pressure.

Question. Define the following terms:
(i) Lyophilic colloid,
(ii) Zeta potential,
(iii) Associated colloids.
Answer. (i) Lyophilic colloid: Liquid loving colloidal sols directly formed by mixing substances like gum, gelatin, starch, rubber, etc., with a suitable liquid (the dispersion medium) are called lyophilic sols. e.g., muddy water.
(ii) Zeta potential: The potential difference between the fixed layer and the diffused layer of opposite charges is called the Electrokinetic potential or Zeta potential.
(iii) Associated colloids: There are some substances which at low concentrations behave as normal strong electrolytes, but at higher concentrations exhibit colloidal behaviour due to the formation of aggregates. The aggregated particles thus formed are called Associated colloids or Micelles.

Long Answer Type Questions

Question. Define the following:
(i) Gold Number
(ii) Hardy-Schulze rule
(iii) Zeta Potential
(iv) CMC
(v) Electrophoresis 
Answer. (i) The number of milligram of protective collides which must be added to 10 ml of given gold sol to prevent it from coagulation by addition of 1 ml of 10% of NaCl.
(ii) The coagulating power of electrolyte increases with increase in charge on the ions used for coagulation e.g., Al³⁺ > Ba²⁺ > Na⁺ for negatively charged colloids.

[Fe(CN)₆]^4– > PO₄^3– SO₄^2– > Cl^– for positively charge d colloids.
(iii) The potential difference between the fixed layer and diffused payer of opposite charges is called Zeta Potential.
(iv) Critical micelle concentration is the concentration of a surfactant in the bulk phase above which aggregates of surfactant molecules start formation of micelle.
(v) The movement of colloidal particles under the influence of an electric field where negatively charged particles move towards the cathode and positively charged particles move towards anode.

Question. Differentiate between multi-molecular and macro- molecular colloids. Name one example of each. How does associated colloids differ from these two colloids?
Answer. (i) In multi-molecular colloids, the colloidal particles are aggregate of atoms or small molecules with a diameter of less than 1nm. The molecules in the aggregate are held together by Van der Waals forces of attraction. Examples of such colloids include Gold sol and Sulphur sol.
(ii) In macro-molecular colloids, the colloidal particles are large molecules having colloidal dimensions.
These particles have a high molecular mass.
When these particles are dissolved in a liquid, sol is obtained.
For example : Starch, Nylon, Cellulose, etc.
(iii) Certain substances tend to behave like normal electrolytes at lower concentrations.
However, at higher concentrations these substances behave as colloidal solutions due to the formation of aggregated particles. Such colloids are called aggregated colloids.