Explore topic-wise InterviewSolutions in .

(ii) increase in temperature

(b) Silica gel

(iv) high temperature

 (a)  2 3 4 1

1. Chemisorption is highly specific.

2. Chemisorption involves compound formation and hence is irreversible in nature.

(i) Litmus is the adsorbate and charcoal is the adsorbent. 

(ii) The material providing the surface upon which absorption occurs, is known as the adsorbent and the substance adsorbed is called adsorbate. 

(iii) The process of removal of adsorbed substance from the surface of the adsorbent is called desorption. 

(iv) The phenomenon in which absorption and adsorption occur together is called sorption.

Ethyl alcohol vapours. It is an adsorbate whereas others are adsorbents.

Correct answer is (iv) H₂

Colloids can be classified on various bases: 

(i) On the basis of the physical state of the components (by components we mean the dispersed phase and dispersion medium). Depending on whether the components are solids, liquids, or gases, we can have eight types of colloids. 

(ii) On the basis of the dispersion medium, sols can be divided as

(iii) On the basis of the nature of the interaction between the dispersed phase and dispersion medium, the colloids can be classified as lyophilic (solvent attracting) and lyophobic (solvent repelling).

1. If the dispersion medium considered as water, then the colloids are referred as hydrosols (or) aquasols.

2. If the dispersion medium is an alcohol, the colloid is termed as alcosol. and if benzene is the dispersion medium, it is called benzosol.

1. Oxidation method: When hydroiodic acid is treated with iodle acid J, sol is obtained.

HIO₃ + 5HI → 3H₂O + 3I_2(sol)

2. Reduction method: Gold sol is prepared by reduction of aune chloride using formaldehyde. 

2 AuCl₃ + 3HCHO + 3H₂O → 2 Au_(sol) + 6HCI + 3HCOOH

3. Hydrolysis: Ferric chloride is hydrolysed to get ferric hydroxide colloid

FeCl₃ + 3H₂O → Fe(OH)₃(sol) + 3HCI 

4. Double decomposition: When hydrogen suiphide gas is passed through a solution of arsenic oxide, a yellow coloured arsenic sulphide is obtained as a colloidal solution.

As₂O₃ – 3H₂S → As₂S₃ + 3H₂O

5. Decomposition: When few drops of an acid is added to a dilute solution of sodium thiosulphate, sulphur colloid is produced by the decomposition of sodium thio sulphate.

S₂O₃^2- + 2H⁺ → S_(sol) + H₂O + SO₂

(a) colloid mill

(b) Sved berg

Physical adsorption 

1. Forces of attraction between the adsorbent and adsorbate molecules are weak Van der Waals’ forces,

2. Heat of adsorption is low (20-40 kJ mol¹) 

3. It is temporary and reversible.

Chemical adsorption 

1. Forces between the adsorbent and the adsorbate are strong chemical bond. 

2. Heat of adsorption is high (80-24OkJ mol¹) 

3. It is permanent and irreversible.

(d)  3 1 4 2

(a)  2 4 1 3

(c) 400 kJ/mole

Activity: Activity of a catalyst refers to the ability of a catalyst to increase the rate of chemical reaction. 

For example : H₂ and O₂ presence of platinum react to form water explosively.

2H₂ + O₂ + Pt → 2H₂O

Selectivity: Selectivity of a catalyst is its ability to speed up a reaction to yield a particular product.

For example : CO + H₂ combine to form CH₄ when Ni is the catalyst and methanol when Cr₂O ₂ is catalyst.

CO(g) +  H₂ → HCHO(g)

Characteristics of enzyme catalysis: 

(i) High efficiency: A single molecule of enzyme can transform one million molecules of the reactant per minute. 

(ii) High specificity: Each enzyme is specific for a given reaction.

(iii) Highly active under optimum temperature (25° - 35°C). 

(iv) Highly active under optimum pH. 

(v) Enzyme activity increases in the presence of coenzymes. 

(vi) Influence of inhibitors and poisons. 

(vii) Enzyme do not alter final state of equilibrium.

To make the surface available again for more reaction to occur/To remove the product formed from the surface of the catalyst.

(b)  4 3 2 1

(c) Occlusion

When adsorption and absorption both takes place simultaneously is known as Sorption.

The gas molecules diffuse onto the surface of the catalyst and get absorbed. After the chemical change, the products formed diffuse away from the surface of the catalyst setting the surface free for other reactant molecules to adsorb on the surface and give the product.

Activation of adsorbent increases the adsorption power of the adsorbent. By increasing the surface area of the adsorbent,

1. Removing the gases already adsorbed and

2. Making the surface of adsorbent rough.

In heterogeneous catalysis, the reactants are generally gases whereas catalyst is a solid. The reactant molecules are adsorbed on the surface of the solid catalyst by physisorption or chemisorption. As a result, the concentration of the reactant molecules on the surface increases and hence the rate of reaction increases.

Alternatively, one of the reactant molecules undergo fragmentation on the surface of the solid catalyst producing active species which react faster. The product molecules in either case have no affinity for the solid catalyst and are desorbed making the surface free for fresh adsorption. This theory is called adsorption theory.

Those metals which have low melting points. e.g. Tin

(i) In multi-molecular colloids, the colloidal particles are an aggregate of atoms or small molecules with a diameter of less than ⊥ nm. The molecules in the aggregate are held together by Van der Waal’s forces of attraction. Example 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 concentration. However, at higher concentrations, these substances behave as colloidal solutions due to the formation of aggregated particles. Such colloids are called aggregated colloids.

Multimolecular colloids are formed by the aggregation of a large number of small atoms/molecules. The aggregates thus formed have size in the colloidal range, e.g. Gold sol.

Macromolecular colloids contain large size molecules which have the dimensions of colloids, e.g. Starch. Associated colloids behave as electrolytes at low concentration but exhibit colloidal behaviour at higher concentration, e.g. Soap.

Coagulating value of a coagulating ion is directly proportional to the charge on the ion. 

Na₃PO₄ will coagulate a positively charged colloid most easily because it has most negative valence.

a) The method of preparation of ferric hydroxide sol from freshly prepared ferric hydroxide precipitate is called peptization. The method of preparation of ferric hydroxide sol by the addition of ferric chloride solution to boiling water is called hydrolysis,

b) When an electric potential is applied across two platinum electrodes dipped in ferric hydroxide sol electrophoresis will occur. Since ferric hydroxide sol is positively changed the colloidal particles will move towards the platinum electrode which acts as the cathode (negative electrode).

i) A colloid is a heterogeneous system in which one substance called a dispersed phase is dispersed as very fine particles in another substance called a dispersion medium. The particles in a colloid are larger than simple molecules but small enough to remain suspended. The diameter of colloidal particles ranges between 1nm and 1000 nm.

ii)
1) Electrical precipitation of smoke using Cottrell smoke precipitator- Smoke is a colloid of solid particles such as carbon, arsenic compounds, dust etc., in air. These particles are precipitated using high voltage electrodes.

2) Purification of drinking water – The suspended impurities present in water obtained from natural sources is coagulated by adding alum and is made fit for drinking purposes.

3) Medicines – Most of the medicines are colloidal in nature. Colloidal medicines are more effective because they have large surface area and are therefore easily assimilated.

4) In the rubber industry – Rubber latex is a colloid of negatively charged rubber particles which is coagulated to rubber by adding formic acid.

1. Colloids have optical property. When a homogeneous solution is seen in the direction of light, it appears clear but it appears dark in a perpendicular direction. 

2. When light passes through colloidal solution, it is scattered in all direction and it is known as Tyndall effect. 

3. The colloidal particles absorbs a portion of light and remaining portion is scattered from the surface of the colloid. Hence the path of light is made clear.

i) When light passes through colloids the path of light becomes visible. This effect is called Tyndall effect. This is due to scattering of light by colloidal particles.

ii) It state that ‘Thegreaterthe valency of flocculating ion, the greater will be its coagulating, flocculating or precipitating power.

Note:
i) In the coagulation of a positive sol, the flocculating power increases in the order Na⁺ < Ba²⁺ + <AI³⁺
ii) Inthe coagulation of a negative sol, the flocculating power increases in the order Cl < S0²₄ < PO³₄ < [Fe(CN)₆]⁴ Na⁺ < Ba²⁺ < AI³⁺
iii) The lyophilic particles form a layer around the lyophobic particles and thus protect the latter from electrolytes. Such colloids are called protective colloids.

Eg : Gold sol can be protected by adding a little gelatin. Here, gelatin is the protective colloid.

The colloidal impurities present in water get coagulated by added alum, thus making water potable.

(i), (iv)

(i) adsorption of coloured substance

(iv) absoprtion of solvent

The answer is (b) 310 K