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Surface chemistry deals with the phenomenon that occurs on a material’s surface. Some of the significant phenomena in surface chemistry are adsorption and absorption. Adsorption can further be divided into physisorption or chemisorption. Adsorption is a surface phenomenon and its classification can be done on the basis of the interaction involved in the process. The working principle of a catalyst is also a surface phenomena. Additionally, catalysts can be of two types: homogeneous or heterogeneous, depending on the phases of other reactants and products. Another important aspect of surface chemistry is crystallization, which is used to purify substances.
Very Short Answer Questions [1 marks]
Ques. What is a sol?
Ans. A sol is a colloidal solution that has solid particles in a liquid medium. Sols are generally stable in nature and demonstrate the Tyndall effect. Example: cell fluid, paint, etc.
Ques. What is coagulation?
Ans: Coagulation is a process where a liquid changes into a solid or a semi-solid condition. One of the best instances of it is blood coagulation.
Ques. What is the Brownian movement?
Ans. The Brownian motion or movement is an uncontrolled movement of particles in the colloids due to the collision with fast-moving particles in a zig-zag fashion.
Brownian movement
Ques. What is absorption?
Ans. In chemistry, Absorption is a process wherein atoms, ions or molecules are seen to enter a bulk phase – either a solid or liquid material.
Absorption
Ques: How is adsorption dependent on temperature?
Ans: Adsorption is a temperature-dependent phenomenon. This process of adsorption decreases with an increase in temperature, the reason for the same is that it is an exothermic process.
Ques. What is adsorption?
Ans. The process of adsorption is the adhesion of a molecule on the surface of the material. The material which is attached to the surface of the material is adsorbate and the surface itself is called an adsorbent.
Absorption
Ques. Which among AlCl3 or NaCl is more effective during the coagulation of a negative sol?
Ans. AlCl3 is preferred because the charge on Al is higher when compared to Na. The compound with a higher charge is more effective in the process of coagulation.
Ques. What are the two adsorbents which can be used to control humidity?
Ans. The most commonly used compounds for this process are called silica and alumina gel.
Short Answer Questions [2 marks]
Ques. What is the Tyndall effect?
Ans. Tyndall effect is a closely observed phenomenon where the particles in a colloid are seen to scatter the light beams directed at them. This effect is also known as Tyndall scattering. For example, the headlight of vehicles can be seen to work on the principle of the Tyndall effect.
Ques. Establish the difference between a promoter and a poison?
Ans:
| Promoter | Poison |
|---|---|
| A promoter is a substance that enhances the activity of the catalyst, making the reaction faster. | The poison, on the other hand, decreases the activity of the catalyst |
| They will boost the efficiency of the catalyst | They will decrease the efficiency |
Ques: What are dispersion phases and dispersion mediums?
Ans. The dispersed phase is a discontinuous phase, which is composed of particles that are distributed throughout the process. The main difference between the two is that one is continuous and another one is discontinuous.
Ques. Define Emulsion.
Ans: Emulsion is a colloidal solution in which the dispersion phase is a liquid and the dispersing medium is also a liquid. The emulsion can be of two types, oil in water emulsion and water in oil emulsion. The examples of the two types of emulsions are, Milk and cold cream respectively.
Ques. What is the reason for the formation of a delta where the sea and river water meet?
Ans. The muddy river water acts as a colloidal solution and the seawater has electrolytes that help in the coagulation of the river water, thus making the delta.
Ques. Why is the process of physisorption reversible whereas chemisorption is not?
Ans. The forces of attraction in physisorption are much weaker than chemisorption and no new compound is formed during this process therefore it is a reversible process. In the case of chemisorption, the forces of attraction are strong bonds which also lead to the formation of new compounds thus making this process irreversible.
Long Answer Questions [3 marks]
Ques. What are the types of adsorption?
Ans. The two primary types of adsorption are physical adsorption and chemical adsorption. Physical adsorption also called Physisorption is the reversible process in which the interaction between the adsorbate and adsorbent is weak Van Der Waal’s forces. The other chemical adsorption is also known as chemisorption is an irreversible process. In this strong chemical bonds are formed and new compounds are formed.
Ques. Explain what is ‘Ostwald process’ and also name the catalyst used in it.
Ans. Ostwald’s process is for the production of nitric acid that was first developed by Wilhelm Ostwald. The catalyst which is used in this process is Platinum. It is a two-step process, where the first step includes the generation of nitric oxide by oxidation of ammonia along with nitrogen dioxide. The second step is the absorption of nitrogen dioxide produced on water, this, in turn, forms nitric acid.
Ostwald process
Ques. What is Freundlich adsorption isotherm?
Ans. Freundlich Adsorption Isotherm is an empirical relationship between the quantity of the gas which is adsorbed into the solid surface and the gas pressure. Alongside that, adsorption isotherms is a plot between the extent of adsorption, i.e., x/m and the pressure of the gas at a constant temperature.
Freundlich Adsorption Isotherm
Ques. What is the difference between a catalyst and an enzyme?
Ans:
| Catalyst | Enzyme |
|---|---|
| Catalysts are chemicals that affect the rate of the reaction. However, they do not change the rate of the reaction. | Enzymes are proteins that catalyze a reaction. |
| Inorganic catalysts have comparatively low molecular weight. | They have a higher molecular weight. |
| They can increase the rate of reaction for a diverse range of reactions. | Enzymes are specific to a certain reaction. |
| They act on physical reactions. | They act on the chemical reaction. |
Very Long Answer Questions [5 marks]
Ques. What is the difference between physisorption and chemisorption?
Ans:
| Physisorption | Chemisorption |
|---|---|
| It is a reversible process. | It is an irreversible process. |
| It is a type of adsorption process where weak interactions like Van Der Waal’s forces are formed between the adsorbent and adsorbate. | In this, the interaction between the adsorbent and adsorbate is strong chemical bonds. |
| No new compound is formed during this process. | A new compound is formed in this process. |
| Enthalpy of adsorption is low. | Enthalpy of adsorption is high in this process. |
| Very low or no activation energy is needed in this process. | High activation energy is needed to initiate the process. |
| This type of adsorption is not specific. | This process is highly specific. |
Ques. What is the difference between Adsorption and Absorption?
Ans:
| Adsorption | Absorption |
|---|---|
| It is the process in which there is an attraction or retention of the molecule on the surface. | In this process, the molecule is not on the surface but gets uniformly distributed throughout the liquid. |
| It is a surface phenomenon | In this the whole mass of the absorbent is concerned. It is a bulk phenomenon |
| It is a fast process but slows down at equilibrium. | It occurs at a uniform rate. |
| It is a temperature dependant phenomenon | This process is not affected by temperature |
| It is an exothermic reaction | This process is an endothermic reaction. |
Ques. What is a catalyst? Establish the difference between homogeneous and heterogeneous catalysts?
Ans. A catalyst is a substance that helps increase the rate of reaction of a chemical reaction. This is done by lowering the activation energy of the reaction but the catalyst does not undergo any permanent chemical change. Two types of catalysts are present that are homogeneous and heterogeneous catalysts.
| Homogeneous catalyst | Heterogeneous catalyst |
|---|---|
| The reaction medium and the catalyst are in the same phase. | They have distinct solid phases. |
| They are usually difficult to separate. | They can get easily separated. |
| Homogeneous catalysts cannot be recycled easily as they are expensive and difficult to be separated. | They can be easily separated and reused. |
| Not diffusion-controlled. | This can be diffusion controlled. |
| They have a shorter life span when compared to the heterogeneous catalyst. | Longer life span. |
| The purification steps required for homogeneous catalysts are very extensive. | Heterogeneous catalysts involve fewer steps in the process of purification. |
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