Surface Chemistry

JEE Chemistry · 85 questions · Page 3 of 9 · Click an option or "Show Solution" to reveal answer

Q21

A 42.12% (w/v) solution of NaCl causes precipitation of a certain sol in 10 hours. The coagulating value of NaCl for the sol in 2 hours is : [Given : Molar mass : Na = 23.0 g mol

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1 ; Cl = 35.5 g mol

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A 36 m mol L

-

B 36 mol L

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C 1440 mol L

-

D 1440 m mol L

-

Correct Answer

Option D

Solution

Data is insufficient.

Q22

The Zeta potential is related to which property of colloids?

A Colour

B Tyndall effect

C Charge on the surface of colloidal particles

D Brownian movement

Correct Answer

Option C

Solution

The potential difference between the fixed layer and the diffused layer of opposite charges is called zeta potential.

It is related to the charge on the surface of colloidal particles.

Q23

Incorrect statement for Tyndall effect is :

A The refractive indices of the dispersed phase and the dispersion medium differ greatly in magnitude.

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

C During projection of movies in the cinemas hall, Tyndall effect is noticed.

D It is used to distinguish a true solution from a colloidal solution.

Correct Answer

Option B

Solution

For Tyndall effect, the diameter of the dispersed particles is not much smaller than the wavelength of the light used.

Q24

Using very little soap while washing clothes, does not serve the purpose of cleaning of clothes, because :

A soap particles remain floating in water as ions.

B the hydrophobic part of soap is not able to take away grease.

C the micelles are not formed due to concentration of soap, below its CMC value.

D colloidal structure of soap in water is completely disturbed.

Correct Answer

Option C

Solution

The little amount of using soap while washing clothes, does not serve the purpose of cleaning of clothes because the micelles are not formed due to the low concentration of soap as it is below CMC.

Q25

For micelle formation, which of the following statements are correct? A. Micelle formation is an exothermic process. B. Micelle formation is an endothermic process. C. The entropy change is positive. D. The entropy change is negative.

A A and D only

B A and C only

C B and C only

D B and D only

Correct Answer

Option C

Solution

Micelle formation is an endothermic process with positive entropy change.

Q26

100 \mathrm{~mL}

5 \%\,(\mathrm{w} / \mathrm{v})

solution of

\mathrm{NaCl}

in water was prepared in

250 \mathrm{~mL}

beaker. Albumin from the egg was poured into

\mathrm{NaCl}

solution and stirred well. This resulted in a/an :

A Lyophilic sol

B Lyophobic sol

C Emulsion

D Precipitate

Correct Answer

Option A

Solution

Albumin from the egg was poured into $100 \mathrm{~mL}$ of $5 \%$ (w/v) $\mathrm{NaCl}$ solution in water.

This would result in the formation of lyophilic sol.

Albumin molecules get dispersed in water the colloidal particles of albumin are stabilised by hydrogen bond with water molecules.

Q27

Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A) : In expensive scientific instruments, silica gel is kept in watch-glasses or in semipermeable membrane bags. Reason (R) : Silica gel adsorbs moisture from air via adsorption, thus protects the instrument from water corrosion (rusting) and / or prevents malfunctioning. In the light of the above statements, choose the correct answer from the options given below :

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

B (A) is true but (R) is false

C (A) is false but (R) is true

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

Correct Answer

Option A

Solution

Assertion is correct and Reason is correct explanation of Assertion.

Silica gel adsorbs moisture and thus products the instrument from water corrosion (rusting) and prevents malfunctioning.

Q28

Statement I : For colloidal particles, the values of colligative properties are of small order as compared to values shown by true solutions at same concentration. Statement II : For colloidal particles, the potential difference between the fixed layer and the diffused layer of same charges is called the electrokinetic potential or zeta potential. In the light of the above statements, choose the correct answer from the options given below

A Both Statement I and Statement II are false

B Statement I is true and Statement II is false

C Both Statement I and Statement II are true

D Statement I is false but Statement II is true

Correct Answer

Option B

Solution

Statement I: For colloidal particles, the values of colligative properties are of small order as compared to values shown by true solutions at the same concentration.

This statement is true.

Colloidal particles are intermediate in size between true solutions and suspensions, and their properties differ from those of true solutions.

The colligative properties of colloids, such as osmotic pressure and vapor pressure, are of a smaller order of magnitude than those of true solutions with the same concentration.

Statement II: For colloidal particles, the potential difference between the fixed layer and the diffused layer of same charges is called the electrokinetic potential or zeta potential.

This statement is false.

For colloidal particles, the potential difference between the fixed layer and the diffused layer of opposite charges is called the electrokinetic potential or zeta potential.

Q29

Given below are two statements, one is labelled as Assertion A and the other is labelled as Reason R. Assertion A : The diameter of colloidal particles in solution should not be much smaller than wavelength of light to show Tyndall effect. Reason R : The light scatters in all directions when the size of particles is large enough. 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 A is true but R is false

C Both A and R are correct but R is NOT the correct explanation of A

D A is false but R is true

Correct Answer

Option A

Solution

Tyndall effect is observed only when the following two conditions are satisfied (a) The diameter of the dispersed particle is not much smaller than the wave length of light used. (b) Refractive indices of dispersed phase and dispersion medium differ greatly in magnitude.

Q30

What happens when a lyophilic sol is added to a lyophobic sol?

A Film of lyophobic sol is formed over lyophilic sol.

B Lyophilic sol is dispersed in lyophobic sol.

C Film of lyophilic sol is formed over lyophobic sol.

D Lyophobic sol is coagulated

Correct Answer

Option C

Solution

When a lyophilic sol is added to a lyophobic sol, the lyophilic sol forms a protective film around the lyophobic sol particles, preventing their aggregation or coagulation.

This process is known as "protection" and is used to stabilize lyophobic sols.

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