Recent questions tagged surface-chemistry

Description : Why is ferric chloride preferred over potassium chloride in case of a cut leading to bleeding?

Last Answer : Ans.: Blood is negatively charge colloidal particles. It is coagulated by +ve ions. As Fe ++ ions has greater number of charges than K+ ions. Therefore on the basis of Hardy-Schulze rule, Coagulation with Fe+++ is faster and hence it is preferred. 

Description : How can a colloidal solution and true solution of the same colour be distinguished from each other?

Last Answer : Ans.: By Tyndal effect( colloidal solution will scatter light and path becomes lighted where as no such phenomena is observed in true solution.)

Description : What is similarity and dissimilarity in aqua solution and solid aerosols?

Last Answer : Ans. Aqua Sols and solid aerosols both have solid as dispersed phase and have different dispersion medium. Aqua solution contain water and aerosol contain air as dispersion medium. 

Description : Which will be adsorbed more readily on the surface of charcoal and why NH3 or CO2?

Last Answer : Ans: The critical temperature NH3 is more CO2, therefore NH3 is liquefied more easily than CO2. Hence NH3 has higher intermolecular forces of attraction and hence it adsorbed more readily. 

Description : Why it is necessary to remove CO when ammonia is obtained by Haber’s process?

Last Answer : Ans.: Because CO acts as poison for the catalyst in the manufacture of NH3 by Haber’s process. 

Description : Why are substances like Platinum and Palladium offer used for carrying out electrolysis in aqueous solution ?

Last Answer : Platinum and palladium is inert electrodes. They are not react with the ions of electrolyte and products of electrolysis. Hence they are used as electrodes during electrolysis. Hence they ... electrodes during electrolysis. Hence they are used as electrodes during electrolysis in aqueous solution. 

Description : Comment on the statement that “ colloid is not a substance but state of a substance” .

Last Answer : Ans. A substance shows different physical properties in different medium. It may exist as colloid or crystalloids under certain conditions. Eg. NaCl in water behaves like crystalloid while in benzene behaves like colloid ... the particles lies in the range 1 to 1000 no., it is in colloidal state. 

Description : Explain the following terms : (i) Electrophoresis, (ii) Coagulation, (iii) Dialysis (iV) Tyndal Effect

Last Answer : (i) Electrophoresis :- The immigration of colloidal solute towards oppositely charged electrode under an electric potential is called Electrophoresis.  (ii) Coagulation :- The process of settling down ... The scattering of light in colloidal solution by colloidal solute is known as Tyndal effect.

Description : Why adsorption is always exothermic?

Last Answer : Ans.: In Adsorption, change of entropy ΔS is –ve i.e. non favourable condition for exothermic change where as change of enthalpy ΔH is –ve i.e. favourable condition for exothermic change. Overall ΔG becomes –ve in adsorption; therefore adsorption is always exothermic.

Description : What do you mean by activity and selectivity of catalysis? 

Last Answer : Ans. Activity of catalyst means to increase the extent of chemisorption. Selectivity of Catalyst means to direct a reaction to form selective product.

Description : What is observed (i) When a beam of light is pressed through a colloidal sol (ii) An electrolyte, NaCl is added to hydrated ferric oxide sol. (iii) Electric current is passed through colloidal sol.

Last Answer : Ans.: (i) Tyndal Effect (iv) Coagulation (v) Electrophoresis

Description : Discuss the effect of pressure and temperature on the adsorption of gases on solids

Last Answer : Ans: Effect of pressure : By the increase of temp., extent of adsorption decreases uniformly for physisorption but for chemisorption initially increases then decreases. 

Description : What do you mean by activation of adsorbant? How is it achieved?

Last Answer : Ans.: Activation of adsorbent means increase the extent of adsorption. It is achieved by the increase of surface area. 

Description : Why are powdered substances more effective absorbents than their crystalline forms?

Last Answer : Ans. Due to increase of surface area of powered substances. 

Description : Why does physisorption decrease with increase of temperature ?

Last Answer : Ans.: Because the attraction between gas molecules and solid surface is very weak which easily over come by increase of temperature.

Description : What is common to aquasol and aerosol ? In what respect do they differ ?

Last Answer : Both are colloids. In aquasol, water acts as dispersion medium. In aerosol, air acts as dispersion medium.

Description : What type of colloidal sols are formed in the following ? (i) Sulphur vapours are passed through cold water. (ii) White of an egg is mixed with water. (iii) Concentration of soap solution is increased.

Last Answer : (i) Multimolecular colloid (ii) Macromolecular colloid (iii) Associated colloid.

Description : What is meant by induced catalysis ? Give an example.

Last Answer : It is a phenomenon in which a chemical reaction increases the rate of another reaction which otherwise may not occur in similar conditions.  Eg. Sodium arsenite (Na3AsO3 ) is not oxidised in air but if ... a solution containing Na3AsO3 and Na2 SO3 , then both AsO3 3- and SO3 2- ions are oxidised.

Description : Why physical adsorption is multimolecular whereas chemisorption is unimolecular ?

Last Answer : Chemisorption takes place as a result of reaction between adsorbent and adsorbate. When the surface of the adsorbent is covered with one layer, no further reaction can take place. Physical adsorption is ... any number of layers may be formed one over the other on the surface of the adsorbent.

Description : SnO2 forms a positively charged colloidal sol in acidic medium and a negatively charged sol in the basic medium. Why ? 

Last Answer : Ans. SnO2 is amphoteric in nature. It reacts with acid eg. HCl to form SnCl4 in the solution. The common Sn4+ ions are adsorbed on the surface of SnO2 particles giving them a positive ... solution. The stannate ions are adsorbed on the surface of SnO2 particles giving them a negative charge. 

Description : Addition of H2 to acetylene gives ethane in presence of palladium but if BaSO4 and quinoline or sulphur are also added, the product is ethane. Why ?

Last Answer : Ans. BaSO4 + quinoline / s poison the catalyst. Hence, the efficiency of the catalyst decreases and the reaction stops at the first stage of reduction. 

Description : Why the sun looks red at the time of setting ? Explain on the basis of colloidal properties.

Last Answer : Ans. At the time of setting, the sun is at the horizon. The light emitted by the sun has to travel a longer distance through the atmosphere. As a result, blue part of the light is scattered away by the dust particles in the atmosphere. Hence the red part is visible.

Description : What is collodion ? What is its use ? 

Last Answer : Ans. Cellulose dispersed in ethanol, is called collodion. It is used for making membranes for ultrafiltration.

Description : What is the function of gum arabic in the preparation of Indian ink ?

Last Answer : Ans. Gum arabic is a protective colloid and thus provides stability to Indian ink. 

Description : Dialysis is a method of purification of sols. But prolonged dialysis of the sol makes it unstable. Why ?

Last Answer : Ans. Traces of electrolytes in the sol, impart charge to dispersed phase particles making it stable. Prolonged dialysis removes all electrolytes thus making the sol unstable.

Description : What is the purpose of adding gelatin to ice cream ?

Last Answer : Ans. Ice cream is a colloid. Gelatin imparts stability to it because gelatin is a protective colloid. 

Description : Bleeding is stopped by the application of alum to a wound. Why ?

Last Answer : Ans. Blood is a colloid alum being an electrolyte, makes the blood to coagulate and form clot.

Description : What is the unit for expressing flocculation value ?

Last Answer : Ans. millimole per litre. 

Description : Out of NaCl, MgSO4 , Al2 (SO4 ) 3 , K4 [Fe(CN)6 ], which one will bring about the coagulation of a gold sol quickest and in the least of concentration ?

Last Answer : Ans. Al2 (SO4 ) 3 .

Description : What happens to a gold sol if gelatin is added to it ?

Last Answer : Ans. It causes stabilisation of gold sol. 

Description : What happens when freshly precipitated Fe (OH)3 is shaken with a little amount of dilute solution of FeCl3 ?

Last Answer : Ans. It causes peptization leading to the formation of a positively charged sol of Fe (OH)3 

Description : If we add equimolar amounts of ferric hydroxide sol and arsenic sulphide sol, what will happen ?

Last Answer : Ans. Both the sols will get coagulated. 

Description : A sol is prepared by addition to excess AgNO3 solution in KI solution. What charge is likely to develop on the colloidal particles ?

Last Answer : Ans. Positive. 

Description : On passing H2 S through dilute HNO3 the colourless solution becomes turbid. Why ? 

Last Answer : Ans. Due to formation of colloidal sol of Sulphur. 

Description : Out of CO and NH3 which is adsorbed on activated charcoal to a large extent and why ?

Last Answer : Ans. Ammonia; because more easily liquefiable gas undergoes adsorption to a greater extent.

Description : The formation of micelles occurs only beyond a certain temperature. What is the temperature called ?

Last Answer : Ans. Kraft temperature  

Description : Out of glucose, urea and dodecyl trimethyl ammonium chloride, which one forms micelles in aqueous solution above certain concentration ?

Last Answer : Ans. Dodecyl trimethyl ammonium chloride. 

Description : If an electric field is applied to a colloidal sol, the dispersed phase particles are found to move towards the electrode of opposite charge. If however, the dispersed phase is made stationary, the ... move in the opposite direction. What is the term used for such movement of dispersion medium ?

Last Answer : Ans. Electro osmosis. 

Description : A liquid is found to scatter a beam of light but leaves no residue when passed through the filter paper. What can the liquid be described as ?

Last Answer : Ans. Colloid. 

Description : What is the term used for minimum concentration of an electrolyte which is able to cause coagulation of a sol ?

Last Answer : Ans. Flocculation value. 

Description : At high pressure, the entire metal surface gets covered by a mono molecular layer of the gas. What is the order of the process ?

Last Answer : Ans. Zero order. 

Description : The colloidal solution of gold prepared by different methods have different colours. Why ?

Last Answer : Ans. Due to difference in the size of colloidal particles. 

Description : Which type of metals act as effective catalysts ?

Last Answer : Ans. Transition metals. 

Description : Cottrell Smoke precipitator

Last Answer : Cottrell Smoke precipitator : Smoke is a colloidal solution of solid particles like C, As compounds and dust in air. It comes out through the chimneys of industrial plants. It consists ... discharged towards oppositely charged metal disc in form of precipitate while gases come out through chimney. 

Description : Defination of Emulsion

Last Answer : Emulsion : A colloids contain dispersed phase and dispersion medium both in liquid state is known as Emulsion.  There are two types of emulsion. (i) Oil in water & (ii) water in oil.

Description : Defination of Coagulative Value

Last Answer : Coagulative Value : The minimum no. of a milli moles of electrolyte requires to coagulate one litre colloidal solutions.

Description : Defination of Coagulation

Last Answer : Coagulation : The process of converting colloidal solution into precipitate by mixing small amount of oppositely charged electrolyte known as Coagulation. 

Description : Defination of Electrophoresis

Last Answer : Electrophoresis : The process of migration of charged colloidal solute towards the oppositely charged electrode in colloidal solution is known as Electrophoresis.

Description : Zeta potential or Electro kinetic potential

Last Answer : Zeta potential or Electro kinetic potential : The potential difference between the fixed layer and the diffused layer of colloidal solution having opposite charges.

Description : Helmholtz Electrical double layer

Last Answer : Helmholtz Electrical double layer : The combination of the two layers of opposite charges around the colloidal solute is called Helmholtz Electrical double layer. When the colloidal particles acquire +ve or -ve ... It attracts counter ions from the medium forming a second layer like.