Tag: surface chemistry

Questions Related to surface chemistry

What is the role of adsorption in froth floatation process used especially for concentration of sulphide ores?

applications of adsorption adsorption adsorption and colloids surface chemistry chemistry

  1. Shape selective catalysts

  2. Adsorption of pine oil on sulphide ore particles

  3. Adsorption of pine oil on impurities

  4. Production of heat in the process of exothermic reaction

Show answer
Correct Option: B
Explanation:
  • In Froth floatation process a low-grade sulphide ore is concentrated by separating it from silica and other earthy matter by this method using pine oil and frothing agent.
  • Pine oil is adsorbed on sulphide ore particles so as to facilitate the further process.

Which is not correct regarding the adsorption of a gas on surface of a solid?

applications of adsorption adsorption adsorption and colloids surface chemistry chemistry

  1. On increasing temp. adsorption increase continuously

  2. Enthalpy & entropy change is Ve

  3. Adsorption is more for some specific substance

  4. Reversible

Show answer
Correct Option: A
Explanation:
Adsorption of gas $\propto$ $\dfrac{1}{temperature}.$
Thus, as the temperature of the gas increases, the gas molecule gets energy and leave the surface. Thus, the rate of adsorption decreases with increase in temperature.

Lake test of $Al^{3+}$ ion is based on adsorption of blue litmus on solid surface of :

applications of adsorption adsorption adsorption and colloids surface chemistry chemistry

  1. $Al$

  2. $Al(OH) _3$

  3. $Al _2O _3$

  4. $AlCl _3$

Show answer
Correct Option: B
Explanation:

Lake test of $Al^{3+}$ ion is based on adsorption of blue litmus on solid surface of $Al(OH) _3$. The dye aluminon is adsorbed by the gelatinous $Al(OH) _3$ precipitate to form lake coloured solution. This test is used as a confirmatory test for $Al^{3+}$ after precipitation of $Al(OH) _3$ with aqueous ammonia.

Which of the following increase(s) the activation of a solid adsorbent?

applications of adsorption adsorption adsorption and colloids surface chemistry chemistry

  1. Polishing the surface of the solid adsorbent.

  2. Sub-dividing the solid adsorbent.

  3. Blowing superheated steam through the porous adsorbent.

  4. Adsorption at very low pressure.

Show answer
Correct Option: B,C
Explanation:

Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid, or dissolved solid to a surface.
Adsorption of gases on solids depends on the following factors:

1) Surface area of the adsorbent: Adsorption is surface phenomenon. The extent of adsorption is directly proportional to the surface area of adsorbent. Finely divided metals and porous solids like charcoal, silica gel etc. posses more surface area when compared with solid lumps. 

2) Effect of pressure: Extent of adsorption increases with an increase in equilibrium pressure.

3) Nature of the gas: Since physical adsorption is non-specific, every gas gets adsorbed on the surface of any solid. Under a given conditions of temperature and pressure, the easily liquefiable gases such as $NH _3, HCl$ and $SO _2$ are adsorbed more than the gases like $H _2, N _2$ and $CO$. The ease with which a gas can be liquefied is determined by its critical temperature, $T _c$. 

Polishing the surface of the solid adsorbent makes no effect on adsorption.

Which of the following is/are application(s) of adsorption?

applications of adsorption adsorption adsorption and colloids surface chemistry chemistry

  1. De-ionization of water

  2. Gas masks

  3. Hygroscopic nature of $CaCl _2$

  4. Heterogeneous catalysis

Show answer
Correct Option: A,B,D
Explanation:
Adsorption :
The phenomenon of attracting and retaining the molecules of a substance on the surface of a liquid or a solid resulting into a higher concentration of the molecules on the surface is called adsorption. As a result of adsorption, there is a decrease of surface energy. The process of removal of an adsorbed substance from the surface on which it is adsorbed is called desorption. It is the reverse of adsorption and can be brought about by heating or by reducing the pressure.

Adsorption finds extensive applications both in research laboratory and in industry. A few applications are discussed below:
In gas masks:
All gas masks are devices containing suitable adsorbent so that the poisonous gases present in the atmosphere are preferentially adsorbed and the air for breathing is purified.
In heterogeneous catalysis:
The action of certain solids as catalysts is best explained in terms of adsorption. The theory is called adsorption theory. According to this theory, the gaseous reactants are adsorbed on the surface of the solid catalyst. As a result, the concentration of the reactants increases on the surface and hence, the rate of reaction increases. The theory is also able to explain the greater efficiency of the catalyst in the finely divided state, the action of catalyst promoters and poisons.
In softening of hard water (De-ionization of water):
The use of ion exchangers for softening of hard water is based upon the principle of competing adsorption just as in chromatography. Hygroscopic nature of $CaCl _2$ is not related to adsorption.

Which of the following is used to adsorb water?

applications of adsorption adsorption adsorption and colloids surface chemistry chemistry

  1. Silica gel

  2. Calcium acetate

  3. Hair gel

  4. Cheese

Show answer
Correct Option: A
Explanation:

Silica gel has a very strong affinity for water and will adsorb it in preference to most other substances. It is also a good adsorbent for HCl, gasoline-range hydrocarbons, sulphur and nitrogen compounds, aromatics and many others. Silica Gel is in wide use in many industries for a myriad number of applications where a high capacity desiccant or selective adsorbent is required.

State one method by which carbon dioxide is removed from the air?

applications of adsorption adsorption adsorption and colloids surface chemistry chemistry

  1. Absorption method

  2. Distillation method

  3. Adsorption method

  4. None of these

Show answer
Correct Option: C
Explanation:
Activated carbon can be used as a $CO _2$ scrubber. Air with high $CO _2$ content mere blew over activated carbon bed and get absorbed.

In  physical adsorption Zeolite(A/B)'s  applications are  seperation of n-paraffins and i paraffins etc.

applications of adsorption adsorption adsorption and colloids surface chemistry chemistry

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

There are several commercial applications based on this mechanism in adsorptive separation processes. One typical example is separating normal paraffin from iso-paraffin and aromatics in an adsorption process using zeolite 5A as an adsorbent.

Removal of chlorine from drinking water in the food industry is done by adsorption :

applications of adsorption adsorption adsorption and colloids surface chemistry chemistry

  1. True

  2. False

Show answer
Correct Option: A
Explanation:

 Activated carbon filtration is a commonly used technology based on the adsorption of contaminants onto the surface of a filter. This method is effective in removing certain organics (such as unwanted taste and odours, micropollutants), chlorine, fluorine or radon from drinking water or wastewater.

Most strongly adsorb component forms lower most band while least adsorb component forms top most band on adsorbent media

applications of adsorption adsorption adsorption and colloids surface chemistry chemistry

  1. True

  2. False

Show answer
Correct Option: B
Explanation:

Most strongly adsorbed component forms the topmost band while  the least adsorbed component forms the lower most band on adsorbent media.