MP Board Class 12th Chemistry Important Questions Chapter 5 Surface Chemistry
Surface Chemistry Important Questions
Surface Chemistry Objective Type Questions
Question 1.
Choose the correct answer :
Question 1.
In the adsorption process of acetic acid on activated charcoal, acetic acid is :
(a) Adsorber
(b) Absorber
(c) Adsorbent
(d) Adsorbate.
Answer:
(d) Adsorbate.
Question 2.
Cause of stability of lyophobic sol is :
(a) Brownian movement
(b) Tyndall effect
(c) Electric charge
(d) Brownian movement and Electric charge
Answer:
(d) Brownian movement and Electric charge
Question 3.
In the coagulation of As2S3 colloidal solution value of whose coagulating power will be minimum :
(a) NaCl
(b) KCl
(c) BaCl2
(d) AlCl3.
Answer:
(d) AlCl3.
Question 4.
Adsorption process is :
(a) Endothermic
(b) Exothermic
(c) No heat change
(d) None of these.
Answer:
(b) Exothermic
Question 5.
Size of colloidal particles in the range of:
(a) 10-7 to 10-9 cm
(b) 10-9 to 10-1 cm
(c) 10-5 to 10-7 cm
(d) 10-2 to 10-8 cm.
Answer:
(c) 10-5 to 10-7 cm
Question 6.
Which of the following is not used for the preparation of lyophilic colloid :
(a) Starch
(b) Gum
(c) Gelatin
(d) Metal sulphide.
Answer:
(d) Metal sulphide.
Question 7.
Sol which can act like a protective colloid :
(a) As2S3
(b) Gelatin
(c) Au
(d) Fe(OH)3.
Answer:
(b) Gelatin
Question 8.
Fog is an example of colloidal system of:
(a) Liquid dispersed in gas
(b) Gas dispersed in gas
(c) Solid dispersed in gas
(d) Solid dispersed in liquid.
Answer:
(a) Liquid dispersed in gas
Question 9.
Gelatin is mostly used in making ice creams in order to :
(a) Prevent forming a colloidal sol.
(b) Enrich the fragrance
(c) Prevent crystallization and stabilize the mixture
(d) Modify the taste.
Answer:
(c) Prevent crystallization and stabilize the mixture
(a) Auto catalyst
(b) Poison
(c) Negative catalyst
(d) Positive catalyst.
Answer:
(b) Poison
Question 11.
The migration of colloidal particles under the influence of electric fields is :
(a) Cataphoresis
(b) Electrodialysis
(c) Electrophoresis
(d) Electrical dispersion.
Answer:
(c) Electrophoresis
Question 12.
Hardy – Schulze law is related with :
(a) Solution
(b) Coagulation
(c) Solids
(d) Gases.
Answer:
(b) Coagulation
Question 13.
How many phases are present in a colloidal solution :
(a) 1
(b) 2
(c) 3
(d) 4.
Answer:
(b) 2
Question 14.
Which is an emulsion among the following :
(a) Air
(b)Wood
(c) Butter
Answer:
(d) Milk.
Question 15.
Butter is :
(a) A gel
(b) An emulsion
(c) A sol
(d) Not a form of colloid.
Answer:
(a) A gel
Question 16.
Sol which acts as protective colloid is :
(a) Gelatin
(b) Au
(c) As2S3
(d) Fe(OH)3
Answer:
(a) Gelatin
Question 17.
Which is not correct for physisorption :
(a) A reversible process
(b) Needs low heat of adsorption
(c) Needs activation energy
(d) Needs low temperature.
Answer:
(c) Needs activation energy
Question 18.
In which among the following is Tyndall effect not expected :
(a) Suspension
(b) Emulsion
(c) Sugar solution
(d) Gold sol.
Answer:
(c) Sugar solution
Question 2.
Answer in one word/sentence :
- Conversion of precipitate into colloidal solution is known as. (MP 2016)
- Dissociation of emulsion into its constituent liquid is known as.
- The catalyst which is used for hydrogenation of oils.
- In dissociation of H2O2, phosphoric acts as which type of catalyst?
- Which catalyst converts glucose into alcohol?
- Cleansing action of soap based on which principle? (MP 2013)
- Who used the word catalyst for the first time? (MP 2013)
- Write the size of colloidal particles.
- What is the effect of temperature on chemical adsorption?
- Why does colloidal particle show Tyndall effect? (MP 2013)
- Movement of particles of colloids is called …………….
- Give an examples of catalytic poisoning.
- Colloidal Solution of liquid in liquid is known as …………… (MP 2012 Supply 18)
Answer:
- Peptization
- Demulsification
- Ni
- Negative
- Zymase
- Emulsification
- Berzellius
- 10-5 to 10-7 cm
- Increases
- Scattering of light by colloidal particles
- As2O3 is contect process
- Brownian movement
- Emulsion.
Question 3.
Fill in the blanks :
- Rate of physical adsorption ………………. with the increase in temperature.
- Particles of As2O3 sol are ……………….
- In the contact process of manufacture of H2SO4 for Pt catalyst ………………. act as
- Oxidation of oxalic acid by KMnO4 is an example of ……………….
- Biological catalysts are necessarily ……………….
- Movement of colloidal particles under the effect of electric field is called ……………….
- Scattering of light by colloidal particles under the effect of electric field is called ……………….
- Intermediate compound theory is applicable to ………………. catalyst.
- The substance on whose surface adsorption takes place is called an ……………….
- Milk is an example of ……………….
- Blood is a ………………. charged colloid.
- Adsorption is an ………………. process.
- Colloidal solution of solid in liquid is called ……………….
- Catalytic promoter substance is ……………….
- On adding electrolyte, precipitation of colloidal particles is known as ……………….
- According to Hardy Schulze law, coagulating capacity of ions depend on the ………………. of ions.
Answer:
- Decreases
- Negatively charged
- As2O3, poison
- Auto catalysis
- Enzyme
- Electrophoresi
- Tyndall effect
- Homogeneous
- Adsorbent
- Emulsion
- Negatively
- Exothermic
- Gel
- Molybdenum
- Coagulation
- Charge.
Question 4.
Match the following :
I.
Answer:
- (f)
- (d)
- (a)
- (c)
- (g)
- (e)
- (b)
- (h).
II.
Answer:
- (c)
- (d)
- (a)
- (b)
- (c)
III.
Answer:
- (e)
- (d)
- (a)
- (b)
- (c)
Surface Chemistry Very Short Answer Type Questions
Question 1.
Why does physisorption decreases with the increase of temperature? (NCERT)
Answer:
It is an exothermic process
Solid + Gas ⇌ Gas/Solid + Heat
Thus, when temperature is raised, reaction proceeds in backward direction and gas adsorbed gets released. It is accordance to Le – Chatelier’s principle.
Question 2.
Why is it necessary to remove CO when ammonia is obtained by Haber’s process? (NCERT)
Answer:
For the preparation of ammonia in Haber’s process solid catalyst is used. It is necessary to remove the CO produced because the gas reacts with iron and forms Fe(CO)5 which exist in liquid state at the temperature of the chamber and obstructs in the production of NH3 because at high temperature CO and H2 react by which production of ammonia decreases. In short CO acts as poison for the iron catalyst used in the process. It is therefore, necessary to remove CO.
Question 3.
Why is adsorption always exothermic? (NCERT)
Answer:
Adsorption leads to decrease in disorder, thus ∆S = +ve. For the process to be performed value of ∆G should be -ve. Thus, in equation ∆G = AH – T ∆S, ∆G will be negative when ∆H will be negative i.e., exothermic. Thus, adsorption is an exothermic process.
Question 4.
What is adsorbent?
Answer:
Solid substances which adsorb the gases or solution are called adsorbent. Like : animal charcoal, silica etc.
Question 5.
What are adsorbate?
Answer:
Gas molecules, vapours or ions which are adsorbed on the surface of solids are called adsorbate.
Question 6.
Delta is formed when river water meets sea water. Explain.
Answer:
In the river water negatively charged particles of soil and sand are present. When river water meets sea – water, various ions Na+, K+ or Mg++ present in sea water causes coagulation and soil particles etc. are settle down. Thus a delta is formed.
Question 7.
How is rain possible by spraying silver iodide on clouds?
Answer:
Clouds are charged due to colloidal nature. Silver iodide is an electrolyte. Spraying it on clouds lead to coagulation by which it rains.
Question 8.
How is the adsorption of a gas related to its critical temperature?
Answer:
Higher is the critical temperature of a gas, greater is the ease of liquification of gas i.e., larger are the van der Waals’ forces of attraction. Therefore, greater is the adsorption.
Question 9.
What happen when a freshly precipitated Fe(OH)3 is shaken with little amount of dilute solution of FeCI3?
Answer:
A reddish brown colloidal solution of Fe(OH)3 is obtained. This process is called peptization. The Fe+3 ions from FeCl3 are absorbed on the surface of the precipitate and form positively charged colloidal solution.
Fe(OH)3 + Fe+3 → [Fe(OH)3] Fe+3
Question 10.
Why is sky blue in colour?
Answer:
Dust particles present in air forms colloidal solution whose particles shows Tyndall effect and hence sky appears blue in colour.
Question 11.
KMnO4 decolourises slowly initially and then rapidly when added to oxalic acid. Why?
Answer:
Addition of KMn04 to oxalic acid oxidises it. Mn+2 ion produced in this reaction acts as autocatalyst and hence decolourisation occur rapidly.
2MnO4– + 5C2O4-2 + 16H– → 2Mn+2 + 10CO2 + 8H2O
Question 12.
How does emulsifier provide stability to emulsion? Write the name of two emulsifiers?
Answer:
For the stability of emulsion, emulsifier is added. Emulsifier forms an interfacial film between the emulsifying medium and the suspended particles. For an oil/water emulsion, protein, gum acts as an emulsifier and for water/oil emulsion salts of fatty acids and heavy metals are the main emulsifier.
Surface Chemistry Short Answer Type Questions
Question 1.
What are emulsions? What are their different types? Give examples of each type. (NCERT)
Answer:
The colloidal system in which dispersed phase and dispersion medium both are liqvid, is called emulsion.
Types of emulsions :
1. Oil in Water type (O/W) : In this type of emulsion small droplets of oil are dispersed in the water or dispersion medium, example Milk, Vanishing cream.
2. Water in Oil (W/O) : In this type of emulsion, small quantity of water is dispersed in the form of droplets in oil (dispersion medium), example Butter, Cod – liver.
Question 2.
What is the difference between multimolecular and macromolecular colloids? Give one example of each. How are associated colloids different from these two types of colloids?
Answer:
1. Multimolecular collodis:
In this type of colloids the colloidal particles consist of aggregates of atoms or small molecules with diameter of less than 1 nm. For example, a gold sol may contain particles of different sizes having several atoms of gold. Similarly sulphur sol contains about one thousand of S8 molecules. These are held together by van derwaals forces.
2. Macromolecular colloids:
In macromolecular colloids the dispersed particles themselves are big molecules, usually polymers. The molecular masses of these macromolecules range from thousands to millions. Synthetic compounds e.g. polyethylene, polystrene, nylon, rubber etc. are macromolecules. Since these molecules have dimensions comparable to those of colloidal particles, there dispersions are known as macromolecular colloids. Most lyophillic sols are of this category.
3. Associated colloids (Micelles):
There are certain substances which behave as normal, strong electrolytes at low concentration, but exhibit colloidal properties at higher concentrations due to the formation of aggregated particles. These are called Micelles. These substances are also called Associated Colloids. Surface active agents like soaps and detergents are of this class.
Question 3.
Explain, what is observed :
- when a Deam oi ngnt is passed through a colloidal sol?
- An electrolyte, NaCI is added to hydrated ferric oxide sol?
- Electric current is passed through a colloidal sol?
Answer:
- Scattering of light by colloidal particles takes place and path of the. light becomes visible (Tyndall effect).
- The positively charged colloidal particles of Fe(OH)3 get coagulated by the oppositely charged CF ions provided by NaCI.
- On passing electric current, the colloidal particles move towards the oppositely charged electrode where, they lose their charge and get coagulated. This is electrophoresis process.
Question 4.
What do you understand by protective colloids?
Answer:
Protective colloid:
On adding small quantity of electrolyte, Lyophobic colloids easily coagulated but if some quantity of hydrophillic colloid is added in Lyophobic colloids, it minimize the effect of addition of electrolyte and coagulation is prevented or very slowly coagulated. This process is called protection of colloid. The hydrophillic colloid which is responsible for protection against coagulation is called protective colloid.
Example:
If a small amount of gum, gelatin or starch is added to As2S3sol, its coagulation of NaCI solution is prevented. Thus starch, gum or gelatin protects the As2S3 sol.
Question 5.
Give the method of preparation of colloidal solution of ferric hydroxide and sulphur in water.
Answer:
1. To prepare sol of ferric hydroxide, FeCl3 solution is added in the boiling water dropwise with shaking. Excess of FeCl3 and HCl are separated by electrodialysis and sol is also stablized by this.
FeCl3 + 3H3O → Fe(OH)3 + 3HCl
2. H2S gas is passed in the solution of nitric acid (oxidising agent) and colloidal solution of sulphur is obtained.
2HNO3 + H2S → S + 2H2O + 2NO2.
Question 6.
What is catalysis? Explain induced catalysis with an example.
Answer:
Catalysis:
A catalyst is a substance which alters the rate of chemical reaction without being used in the reaction and the phenomenon is known as catalysis.
Induced Catalysis:
In induced catalysis, one reaction already taking place, catalyse the other reaction also which does not occur separately.
Example:
Sodium sulphite (Na2SO3) oxidise in the atmosphere easily while sodium arsenite (Na2AsO3) does not oxidise in atmosphere separately. When (Na2SO3) and Na3AsO3 both are kept together, both are oxidised.
Question 7.
What is coagulation? Write Hardy – Schulze’s law.
Answer:
Coagulation:
Colloidal particles are either positively charged or negatively charged. It is seen that on adding some oppositely charged ions or electrolyte, which cancels the charge of colloidal particles and these particles aggregate and change into precipitates. Precipitation of colloidal particles by electrolytes is called coagulation.
Hardy – Schulze’s law:
Coagulating power of an ion is governed by this law according to which, “Greater the valency of an ion greater will be its coagulating power.”
Thus, to coagulate negative sol, the coagulating power of different cations are found to be in the order :
Al3+ > Ba2+ > Na+
Similarly, for the coagulation of a positive sol of Fe(OH)3, the coagulating power of different anions is found to be in the order :
PO43- > SO42- > Cl–
Question 8.
What do you understand by catalytic promoter and catalytic poison? Give an example of each.
Answer:
Catalytic promoter : Chemical substances which are used to increase the activity of the catalyst are known as Catalytic promoter.
Example :
Catalytic poison : Substances which are used to reduce the activity of catalyst are known.
Question 9.
What do you understand by Electro – dialysis?
Answer:
Electro – dialysis:
Particles of true solutions pass through parchment paper or cellophane but sol particles cannot pass through such membranes. In dialysis, the sol filled in a bag of parchment or cellophane is suspended in pure water. This process is very slow and takes a long time for completion. However, it can be quickened under the influence of an electric field and the process is known as Electro – dialysis.
Artificial kidney used in medical science works on the principle of dialysis.
Question 10.
What is homogeneous and heterogeneous catalysis? Explain with example.
Answer:
Homogeneous catalysis:
The chemical reaction in which reactants and cata¬lysts are in same physical state, are example of homogeneous catalysis.
Example : In lead chamber process of manufacturing of sulphuric acid reactant and catalyst NO are in same physical state – gaseous.
Heterogeneous catalysis:
The chemical reactions in which reactants and catalysts are in different physical state, are examples of heterogeneous catalysis.
Example : In Haber process manufacture of Ammonia.
Question 11.
What is ‘Gold number’? Explain with example.
Answer:
Gold Number:
Protective actions of different lyophilic colloids are compared with gold number. Gold number can be defined as:
“Gold number is the number of miligrams of protective colloid (Lyophilic) which on adding prevents the coagulation of 10 ml. standard gold sol by addition of 1 ml. of 10% NaCl solution.” Thus smaller the value of gold number, higher is it’s protecting action. For example, gold number of gelatin and gum arobic are 0.005 and 0.15 respectively. It means gelatin is better protective colloid because it’s only 0 005 mg quantity is required to prevent coagulation if 10 ml Au sol by addition of 1 ml. 10% NaCl.
Question 12.
What is the importance of emulsifying agents in emulsifications?
Answer:
The process of making emulsions is called emulsification. Emulsions are formed when suitable liquids are mixed and shaked, but the emulsions are thus formed are not stable. To make these emulsions stable some other substances are added, which are known as emulsifying agents. Soap, gum, starch etc. act as emulsifying agents. In absence of emulsifying agents, disperse drops of liquid meet each other to distroy emulsion state. It is supposed that emulsifying agents form membrane at interphase of oil and water which checks the union of droplets.
Question 13.
Give reason :
- Milk turns sour on adding acid to it.
- Alum is added to purify water.
- Delta is formed where river water meets sea.
Answer:
1. Milk is an emulsion of fats dispersed in water. Albumin and caesin are emulsifiers. Addition of acid destroys emulsifiers and hence milk gets coagulated.
2. In impure water, soil particles, bacteria and other soluble impurities are dissolved. When alum is added, the Al+3 ion present in alum destroys the negative charge of impure water. Due to neutralization of charge the impurities are coagulated and settle down.
3. In the river water negatively charged particles of soil and sand are present. When river water meets sea – water, various salts present in sea water causes coagulation and soil particles etc. are settle down. Thus a delta is formed.
Question 14.
Explain positive and negative catalysis with example.
Answer:
Positive Catalysis:
When the velocity of any chemical reaction increases with the presence of catalyst, this type of catalysis is called positive catalysis.
Negative Catalysis:
Catalysts when decrease the velocity of chemical reaction are called negative catalysts or retarders and the process is known as negative catalysis.
Question 15.
What is peptization? Explain.
Answer:
Peptization:
Peptization is a good method of preparing colloidal sols from precipitates. A fresh precipitate is taken for the purpose and a suitable reason or peptizing agents are added. These peptizing agents are generally dilute solutions of electrolytes of common ion. Peptization process is opposite of the process of coagulation.
Example:
When fresh precipitate of aluminium hydroxide is boiled with dilute HCl mixed water, colloidal solution of Al(OH)3 is obtained. When an electrolyte is added to a fresh precipitate then the particles of the electrolyte preferentially adsorbs an ion and due to electrostatic repulsion undergo in colloidal state. On adding electrolyte ferric chloride to ferric hydroxide precipitate, sol of ferric hydroxide is obtained.
Question 16.
Write difference between Lyophilic and Lyophobic colloids. (MP2016)
Answer:
Differences between Lyophilic and Lyophobic colloids :
Question 17.
What is Brownian motion?
Answer:
Continuous and zig – zag motion of colloidal particles is called Brownian motion. Such movement was first observed by Robert Brown in 1827, hence it is called Brownian motion. Brownian movement is due to the unequal collision at between molecules of dispersed phase and colloidal particles. On increase of size of colloidal particles or decrease in temperature the motion becomes slower.
Example:
- Zig – zag motion of dust particles entering through ventilator is Brownian motion.
- Lycopodium powder particles move in water due to Brownian motion.
Question 18.
Write difference between Physical adsorption and Chemical adsorption.
Answer:
Differences between Physical adsorption and Chemical adsorption :
Physical adsorption:
- Low value of enthalpy of adsorption (20 – 40 kJ mol-1)
- This type of adsorption involves weak ‘van der Waals’ forces between adsorbent and adsorbate.
- Usually takes place at low tempera¬ture and decreases with increase in temperature.
- It is reversible in nature.
- The extent of adsorption is approxi-mately related to the case of liquification of the gas.
- Forms multimolecular layers.
- On increasing pressure, adsorption also increases.
Chemical adsorption:
- High value of enthalpy of adsorption (40 – 400kJmol-1)
- This type of adsorption involves strong forces of attraction due to chemical bond formation.
- Takes place at high temperature.
- It is irreversible.
- No such correlation.
- Forms monomolecular layers.
- No any effect of pressure.