Surface Chemistry Test

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Surface Chemistry Test - 11

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Weekly Quiz Competition

Question 1
1 / -0

Which of the following statement is incorrect regarding physisorption?

A
It occurs because of Van der Waals' forces.

B
More easily liquiefiable gases are adsorbed readily.

C
Under high pressure, it results into multi molecular layer on adsorbent surface.

D
Enthalpy of adsorption $$(\Delta \mathrm{H}_{\mathrm{a}\mathrm{d}\mathrm{s}\mathrm{o}\mathrm{r}\mathrm{p}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}})$$ is low and positive.

Solution

Enthalpy of adsorption in physisorption is negative as the process is exothermic.

$$\Delta \mathrm{G}=\Delta \mathrm{H}-\mathrm{T}\Delta \mathrm{S}$$

The entropy decreases $$(\Delta \mathrm{S}= - \mathrm{v}\mathrm{e})$$ because of adsorption.

But the overall process is spontaneous. Therefore, the $$\Delta \mathrm{H}$$ must be negative having a low magnitude.

Therefore, the spontaneous adsorption will have negative enthalpy change.

Thus, the statement $$\text{D}$$ is incorrect.

Hence, the correct option is $$\text{D}$$
Question 2
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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
Adsorption is monolayer

B
Energy of activation is low

C
Adsorption increases with increase in temperature

D
Enthalpy of adsorption is greater than 100 kJ mol$$^{-1}$$

Solution

Physical adsorption process (physisorption) has the following characteristics : (i) It arises due to van der Waals forces and (ii) it is reversible. The correct statement that describes the above adsorption process is option B. Energy of activation for physisorption is low.
Physisorption is multilayer. It decreases with increase in temperature and the enthalpy of physisorption is low $$(20-40$$ kJ/mol$$)$$.
Question 3
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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
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.

C
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 solution and homogenize with a mechanical shaker

D
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.

Solution

The most appropriate method of making egg-albumin solution is by breaking an egg carefully and transfer the transparent part of the content to 100 mL of $$5$$% w/V saline solution and stir well.

Note: Egg-albumin is the transparent part of the egg. During the preparation of the solution, water should be cold. If we boil water, the solution will be coagulated.
Question 4
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$$3$$ g of activated charcoal was added to $$50$$ mL of the acetic acid solution $$(0.06\ N)$$ in a flask. After an hour, it was filtered and the strength of the filtrate was found to be $$0.042\ N$$. The amount of acetic acid adsorbed (per gram of charcoal) is :

A
$$18$$ mg

B
$$36$$ mg

C
$$42$$ mg

D
$$54$$ mg

Solution

$$50$$ mL of $$0.06\ N$$ acetic acid solution contains $$0.06\ mol/L$$ $$\times \dfrac {50\: mL}{1000\: mL/L} \times 60 \: g/mol = 0.180 \ g$$ of acetic acid.

After filtration, $$50$$ mL of $$0.042\ N$$ acetic acid solution contains $$0.042 \: mol/L \times \dfrac {50 \ mL}{1000 \ mL/L}= 0.126 \ g$$ of acetic acid.

Hence, the amount of acetic acid adsorbed on $$3\ g$$ of activated charcoal is $$0.180 \: g - 0.126 \: g = 0.054 \: g$$. This is equal to $$54\ mg$$.

Hence, the amount of acetic acid adsorbed on $$1\ g$$ of activated charcoal is $$\dfrac {54 \: mg \times 1 \: g}{3 \: g}=18 \: mg$$.
Question 5
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Which one of the following is not a property of physical adsorption?

A
Lower the temperature, more the adsorption

B
Greater the surface area, more the adsorption

C
Higher the pressure, more the adsorption

D
Unilayer adsorption occurs

Solution

The physical adsorption is temperature and pressure dependent. It increases with increase in pressure and decreases with increase in temperature. Also, when there is more surface area then physical adsorption will be more. Physical adsorption forms multiple layer of adsorption.
Thus, statement given in option $$D$$ is incorrect.
Question 6
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Peptization is a :

A
process of converting a colloidal solution into precipitate

B
process of converting precipitate into colloidal solution

C
process of converting soluble particles to form colloidal solution

D
process of bringing colloidal molecule into solution

Solution

Peptization or Deflocculation is the process responsible for the formation of stable dispersion of colloidal particles in the dispersion medium. In other words, it may be defined as a process of converting a precipitate into colloidal sol by shaking it with a dispersion medium in the presence of a small amount of electrolyte.
Question 7
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Among the following, the surfactant that will form micelles in aqueous solution at the lowest molar concentration at ambient conditions is :

A
$$\mathrm{C}\mathrm{H}_{3}(\mathrm{C}\mathrm{H}_{2})_{15}\mathrm{N}^{+}(\mathrm{C}\mathrm{H}_{3})_{3}\mathrm{B}\mathrm{r}^{-}$$

B
$$\mathrm{C}\mathrm{H}_{3}(\mathrm{C}\mathrm{H}_{2})_{11}\mathrm{O}\mathrm{S}\mathrm{O}_{3}^{-}\mathrm{N}\mathrm{a}^{+}$$

C
$$\mathrm{C}\mathrm{H}_{3}(\mathrm{C}\mathrm{H}_{2})_{6}\mathrm{C}\mathrm{O}\mathrm{O}^{-}\mathrm{N}\mathrm{a}^{+}$$

D
$$\mathrm{C}\mathrm{H}_{3}(\mathrm{C}\mathrm{H}_{2})_{11}\mathrm{N}^{+}(\mathrm{C}\mathrm{H}_{3})_{3}\mathrm{B}\mathrm{r}^{-}$$

Solution

Among the given surfactants, the surfactant that will form micelles in aqueous solution at the lowest molar concentration at ambient conditions is $$\mathrm{C}\mathrm{H}_{3}(\mathrm{C}\mathrm{H}_{2})_{15}\mathrm{N}^{+}(\mathrm{C}\mathrm{H}_{3})_{3}\mathrm{B}\mathrm{r}^{-}$$.

Critical concentration for micelle formation decreases as the molecular weight of hydrocarbon chain of surfactant grows because in this case true solubility diminishes and the tendency of surfactant molecule to associate increases.

The molecular weight is maximum in case of $$\mathrm{C}\mathrm{H}_{3}(\mathrm{C}\mathrm{H}_{2})_{15}\mathrm{N}^{+}(\mathrm{C}\mathrm{H}_{3})_{3}\mathrm{B}\mathrm{r}^{-}$$.
Question 8
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Methylene blue is adsorbed on activated charcoal at $$25^{0}C$$ from its aqueous solution. Which is the correct statement for this process?

A
The adsorption requires activation at $$25^{0}C$$.

B
The adsorption is accompanied by a decrease in enthalpy.

C
The adsorption increases with increase of temperature.

D
The adsorption is irreversible.

Solution

Adsorption of methylene blue on activated charcoal is physical adsorption. Hence, it is characterised by decrease in enthalpy.
Question 9
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The qualitative sketches I, II and III given below show the variation of surface tension with molar concentration of three different aqueous solutions of $$KCl, CH_{3}OH$$ and $$CH_{3}(CH_{2})_{11}OSO_{3}^{-} Na^{+}$$ at room temperature.

The correct assignment of the sketches is:

A
$$I: KCl; II: CH_{3}OH; III: CH_{3}(CH_{2})_{11}OSO^{-}_{3}Na^{+}$$

B
$$I: CH_{3}(CH_{2})_{11}OSO^{-}_{3}Na^{+} II: CH_{3}OH; III: KCl$$

C
$$I: KCl; II: CH_{3}(CH_{2})_{11}OSO^{-}_{3}Na^{+}; III: CH_{3}OH$$

D
$$I: CH_{3}OH; II: KCl; III: CH_{3}(CH_{2})_{11}OSO^{-}_{3}Na^{+}$$

Solution

Impurities affect surface tension appreciably. It is observed that impurities which tend to concentrate on the surface of liquids, compared to its bulk lower the surface tension.

Substances like detergents and soaps $$(CH_3(CH_2)_{11}SO_3^-Na^+)$$ decrease the surface tension sharply.

Those like alcohol $$(eg. CH_3OH, C_2H_5OH)$$ lower the surface tension slightly. This can also be related to the fact that $$CH_3OH$$ has a smaller dielectric constant. The dielectric constant is directly proportional to surface tension. So, on adding $$CH_3OH$$ in water, overall dielectric constant decreases and surface tension decreases.

Inorganic impurities present in the bulk of a liquid such as KCl tend to increase the surface tension of water.
Question 10
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Rate of physisorption increases with:

A
decrease in temperature

B
increase in temperature

C
decrease in pressure

D
decrease in surface area

Solution

The rate of physisorption is inversely proportional to temperature. The rate of physisorption increases with the decrease in temperature as it is an exothermic process.

Option A is correct.

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Surface Chemistry Test - 11

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Question 1

It occurs because of Van der Waals' forces.

More easily liquiefiable gases are adsorbed readily.

Under high pressure, it results into multi molecular layer on adsorbent surface.

Enthalpy of adsorption $$(\Delta \mathrm{H}_{\mathrm{a}\mathrm{d}\mathrm{s}\mathrm{o}\mathrm{r}\mathrm{p}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}})$$ is low and positive.

Solution

Question 2

Adsorption is monolayer

Energy of activation is low

Adsorption increases with increase in temperature

Enthalpy of adsorption is greater than 100 kJ mol$$^{-1}$$

Solution

Question 3

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

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.

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 solution and homogenize with a mechanical shaker

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.

Solution

Question 4

$$18$$ mg

$$36$$ mg

$$42$$ mg

$$54$$ mg

Solution

Question 5

Lower the temperature, more the adsorption

Greater the surface area, more the adsorption

Higher the pressure, more the adsorption

Unilayer adsorption occurs

Solution

Question 6

process of converting a colloidal solution into precipitate

process of converting precipitate into colloidal solution

process of converting soluble particles to form colloidal solution

process of bringing colloidal molecule into solution

Solution

Question 7

$$\mathrm{C}\mathrm{H}_{3}(\mathrm{C}\mathrm{H}_{2})_{15}\mathrm{N}^{+}(\mathrm{C}\mathrm{H}_{3})_{3}\mathrm{B}\mathrm{r}^{-}$$

$$\mathrm{C}\mathrm{H}_{3}(\mathrm{C}\mathrm{H}_{2})_{11}\mathrm{O}\mathrm{S}\mathrm{O}_{3}^{-}\mathrm{N}\mathrm{a}^{+}$$

$$\mathrm{C}\mathrm{H}_{3}(\mathrm{C}\mathrm{H}_{2})_{6}\mathrm{C}\mathrm{O}\mathrm{O}^{-}\mathrm{N}\mathrm{a}^{+}$$

$$\mathrm{C}\mathrm{H}_{3}(\mathrm{C}\mathrm{H}_{2})_{11}\mathrm{N}^{+}(\mathrm{C}\mathrm{H}_{3})_{3}\mathrm{B}\mathrm{r}^{-}$$

Solution

Question 8

The adsorption requires activation at $$25^{0}C$$.

The adsorption is accompanied by a decrease in enthalpy.

The adsorption increases with increase of temperature.

The adsorption is irreversible.

Solution

Question 9

$$I: KCl; II: CH_{3}OH; III: CH_{3}(CH_{2})_{11}OSO^{-}_{3}Na^{+}$$

$$I: CH_{3}(CH_{2})_{11}OSO^{-}_{3}Na^{+} II: CH_{3}OH; III: KCl$$

$$I: KCl; II: CH_{3}(CH_{2})_{11}OSO^{-}_{3}Na^{+}; III: CH_{3}OH$$

$$I: CH_{3}OH; II: KCl; III: CH_{3}(CH_{2})_{11}OSO^{-}_{3}Na^{+}$$

Solution

Question 10

decrease in temperature

increase in temperature

decrease in pressure

decrease in surface area

Solution

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