Surface Chemistry

JEE Chemistry · 85 questions · Page 6 of 9 · Click an option or "Show Solution" to reveal answer

Q51

The aerosol is a kind of colloid in which :

A solid is dispersed in gas

B gas is dispersed in solid

C gas is dispersed in liquid

D liquid is dispersed in water

Correct Answer

Option A

Solution

In aerosol, the dispersion medium is gas while the dispersed phase can be both solid or liquid.

Q52

Kraft temperature is the temperature :

A below which the aqueous solution of detergents starts freezing.

B above which the formation of micelles takes place.

C below which the formation of micelles takes place.

D above which the aqueous solution of detergents starts boiling.

Correct Answer

Option B

Solution

Above Kraft temperature(Tk) the formation of micelles takes place.

Q53

According to Freundlich adsorption isotherm, which of the following is correct ?

{x \over m} \propto {p^0}

{x \over m} \propto {p^1}

{x \over m} \propto {p^{1/n}}

D All the above are correct for different ranges of pressure

Correct Answer

Option D

Solution

The Freundlich adsorption isotherm is mathematically represented as

{x \over m} = k{P^{1/n}}

at high pressure

{1 \over n}

= 0 Hence,

x\,/\,m \propto {p^ \circ }

at low pressure

{1 \over n}

= 1 Hence,

x/m\,\, \propto \,\,p'

Q54

The most appropriate method of making egg-albumin sol is :

A Break an egg carefully and transfer the transparent part of the content to 100 mL of 5% w/V saline solution and stir well

B Break an egg carefully and transfer only the yellow part of the content to 100 mL of 5% w/V saline solution and stir well.

C Keep the egg in boiling water for 10 minutes. After removing the shell, transfer the white part of the content to 100 mL of 5% w/V saline solution and homogenize with a mechanical shaker.

D Keep the egg in boiling water for 10 minutes. After removing the shell, transfer the yellow part of the content to 100 mL of 5% w/V saline solutionand homogenize with a mechanical shaker.

Correct Answer

Option A

Solution

Only the transparent part of an egg has albumin.

Q55

As per Hardy-Schulze formulation, the flocculation values of the following for ferric hydroxide sol are in the order :

A AICl3 > K3[Fe(CN)6] > K2CrO4 > KBr = KNO3

B K3[Fe(CN)6] < K2CrO4 < KBr = KNO3 = AlCl3

C K3[Fe(CN)6] < K2CrO4 < AlCl3 < KBr < KNO3

D K3[Fe(CN)6] > AlCl3 > K2CrO4 > KBr > KNO3

Correct Answer

Option B

Solution

Since, Fe(OH)3 is positively charged sol, hence, anionic charge will flocculate.

As per Hardy Schulze rules coagulation power of anion follows the order : Fe(CN)63–

>

CrO42–

>

Cl– = Br– = NO3– Higher the coagulation power lower will be its flocculation value therefore order will be : Fe(CN)63–

<

CrO42–

<

Cl– = Br– = NO3–

Q56

Tyndall effect is observed when:

A The diameter of dispersed particles is similar to the wavelenght of light used.

B The diameter of dispersed particles is much smaller than the wavelength of light used.

C The diameter of dispersed particles is much larger than the wavelength of light used.

D The refractive index of dispersed phase is greater than that of the dispersion medium.

Correct Answer

Option A

Solution

Diameter of dispersed particles should not be much smaller than wavelength of light used.

Q57

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) : Dissolved substances can be removed from a colloidal solution by diffusion through a parchment paper. Reason (R) : Particles in a true solution cannot pass through parchment paper but the colloidal particles can pass through the parchment paper. In the light of the above statements, choose the correct answer from the options given below :

A Both (A) and (R) are correct and (R) is the correct explanation of (A)

B Both (A) and (R) are correct but (R) is not the correct explanation of (A)

C (A) is correct but (R) is not correct

D (A) is not correct but (R) is correct

Correct Answer

Option C

Solution

Parchment paper is a semi-permeable membrane which allows particles of true solution to pass through as their size are too small.

Assertion is correct but reason is incorrect.

Q58

A particular adsorption process has the following characteristics : (i) It arises due to van der Waals forces and (ii) it is reversible. Identify the correct statement that describes the above adsorption process :

A Enthalpy of adsorption is greater than 100 kJ mol−1.

B Energy of activation is low.

C Adsorption is monolayer.

D Adsorption increases with increase in temperature.

Correct Answer

Option B

Solution

From the given characteristics, the adsorption is an example of physical adsorption. (i) Physical adsorption is multimolecular layer. (ii) It decreases with increase in temperature. (iii) Enthalpy of adsorption is low 20–40 kJ mol−1 for physical adsorption. (iv) Energy of activation is low because in this type of adsorption no chemical reaction takes place.

Q59

Which of the following statements about colloids is False ?

A Freezing point of colloidal solution is lower than true solution at same concentration of a solute.

B Colloidal particles can pass through ordinary filter paper.

C When silver nitrate solution is added to potassium iodide solution, a negatively charged colloidal solution is formed.

D When excess of electolyte is added to colloidal solution, colloidal particle will be precipitated.

Correct Answer

Option A

Solution

Freezing point of colloidal solution is same as true solution at same concentration of a solute.

Q60

The enthalpy change for the adsorption process and micelle formation respectively are

\mathrm{\Delta H_{ads} > 0~and~\Delta H_{mic} < 0}

\mathrm{\Delta H_{ads} > 0~and~\Delta H_{mic} > 0}

\mathrm{\Delta H_{ads} < 0~and~\Delta H_{mic} < 0}

\mathrm{\Delta H_{ads} 0}

Correct Answer

Option D

Solution

Adsorption is the process of a substance (adsorbate) being attracted to a surface (adsorbent).

The enthalpy change for adsorption, $\mathrm{\Delta H_{ads}}$ , is negative because the adsorbent and adsorbate are brought closer together, which releases energy.

Micelle formation is the process of surfactant molecules clustering together in water to form micelles.

The micelles have a hydrophobic (water-repelling) core and a hydrophilic (water-loving) surface.

The enthalpy change for micelle formation, $\mathrm{\Delta H_{mic}}$ , is positive because the surfactant molecules are moving from a state of high entropy (dispersed in water) to a state of low entropy (clustered together).

Here is a table summarizing the enthalpy changes for adsorption and micelle formation: .tg .tg Process Enthalpy change Adsorption $\mathrm{\Delta H_{ads} < 0}$ Micelle formation $\mathrm{\Delta H_{mic} > 0}$

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