CBSE Questions for Class 12 Engineering Chemistry Surface Chemistry Quiz 12 - MCQExams.com

The Tyndall effect is the scattering of light as a light beam passes through a colloid. The individual suspension particles scatter and reflect light, making the beam visible. The amount of scattering depends on the frequency of the light and density of the particles. The angle through which sunlight in the atmosphere is scattered by molecules of the constituent gases varies inversely as the fourth power of the wavelength; blue light will be scattered much more strongly than will the long wavelength red light. The visible beam of headlights in fog is caused by the Tyndall effect. The water droplets scatter the light making the headlight beams visible.

Correct Option: D

Explanation

• Colloids consist of two phases:
  1. Dispersed phase: Component present in small quantity.
  2. Dispersion medium: Component present in excess.
• The particles of the dispersed phase are scattered in the dispersion medium
• When solid particles are dispersed in solid, it is known as $$Solid$$ $$sol$$. Examples include Ruby glass, etc.
• When liquid particles are dispersed in a solid, it is known as $$Gel$$. Examples include cheese, butter, etc.
• When liquid particles are dispersed in a liquid, it is known as $$Emulsion$$. Examples include milk, hair cream, etc.
• When solid particles are dispersed in a liquid, it is called $$Sol$$. Examples include Gold sol, ink, paint, etc.

The heats of adsorption in physisorption or physical adsorption lies in the range of  $$10−40\ kJ/mol$$. It is less as compared to chemisorption as there is no chemical reaction involved in it.

To stop bleeding from an injury, Ferric chloride can be applied because of the following reason:

(A) $$Fe^{3+}$$ ions coagulate blood which is a negatively charged solution
(B) $$Cl^−$$ ions coagulate blood which is a positively charged solution

Blood being a colloidal solution, its coagulation by Hardy-Shuze's law states " Higher the charge on cation higher will be its efficiency to coagulate the colloidal solution" . Thus Option B is correct.

• Catalyst orients the molecules properly, so that reaction occurs

• The heat of adsorption of reactant molecules on a catalyst helps reactants to overcome the activation energy

• A catalyst increases the rate of reaction by decreasing the energy of activation. 
• Hence (i) and (ii) are the correct options.

Chloroform forms a very poisonous compound called phosgene ( $$COCl_2$$) when stored for a long time by reacting with oxygen in presence of sunlight.
$$CHCl_3 + 1/2O_2 \rightarrow COCl_2 + HCl$$ In order to consume that phosgene gas and make chloroform safe, it is mixed with ethanol

Tetraethyl lead (TEL) is added to petrol to retard the ignition of petrol vapours on compression in an internal combustion engine and thus minimise the knocking effect.

$$H_2O_2$$ decomposes to water and oxygen in presence of light that's why it is stored in dark glass bottles. Glycerol is added to it act as negative catalyst

$$NH_3$$ is manufactured by Haber’s process. In this process, pure nitrogen and hydrogen gases react in the ratio of 1:3 in presence of iron as catalyst & molybdenum as promoter.
$$N_2+3H_2 \xrightarrow{Fe/Mo} 2NH_3+ heat$$

Activated charcoal is prepared by heating charcoal with steam to make it more porous.

Chloroform on oxidation produces phosgene gas which is a toxic gas, so as to deaccelerate the reaction we will drop ethanol solution so that this reaction does not occur. So, $$C_2H_5OH$$ is a negative catalyst.

Hence option B is correct.

Hint: The empirical relationship between the quantity of gas adsorbed into the solid surface under the application of pressure is termed as Freundlich adsorption isotherm.

Explanation:

Part: 1

The variation in the amount of gas adsorbed at different pressure conditions is depicted by the curve called adsorption isotherm.

Part: 2

The relationship between the amount og gas adsorbed and pressure is

$$\dfrac{x}{m}\propto  P^{\dfrac{1}{n}}$$

$$\Rightarrow \dfrac{x}{m}=KP^{\dfrac{1}{n}}$$

$$\Rightarrow log\left ( \dfrac{x}{m} \right )=log\left ( k \right )+\dfrac{1}{n}log\left ( P \right )$$

Part: 3 Graphical Representation:

Final answer:

Hence, the graph in option A correctly depicts the physical adsorption isotherm.

Correct Option: $$A$$

• A colloid is a heterogeneous system in which one substance is dispersed (dispersed phase) as very fine particles in another substance called dispersion medium.
  
• Colloidal medicines are more effective because they have large surface area and are therefore easily assimilated.
  

• Purification of drinking water
  
• Cleansing action of soaps and detergents as Medicines
  
• Photographic plates and films