Adsorption and Adsorption isotherm Questions in English

(B) The adsorption process involves the trapping of gas molecules on a solid surface,which restricts their movement. This leads to a decrease in the randomness of the particles,meaning the entropy $(S)$ decreases. Since $\Delta G = \Delta H - T\Delta S$ and for a spontaneous process $\Delta G < 0$,the decrease in entropy $(\Delta S < 0)$ makes the $-T\Delta S$ term positive. For the process to be spontaneous,the enthalpy change $(\Delta H)$ must be negative,making the process exothermic.

(C) The ability of metals to adsorb hydrogen gas is known as occlusion.
The order of adsorption of $H_2$ gas by various metals is:
$\text{Colloidal Palladium} > \text{Palladium} > \text{Platinum} > \text{Gold} > \text{Nickel}$.
Thus,colloidal palladium can adsorb the largest volume of hydrogen gas.

(C) The phenomenon of adsorption of hydrogen gas on the surface of transition metals is specifically known as $Occlusion$.

(C) Sodium hydroxide $(NaOH)$ is widely used in the refining of petroleum and vegetable oils. It acts as a refining agent to remove impurities and decolourise the oils by neutralizing free fatty acids and removing pigments.

(B) Noble gases are present in very small amounts in the atmosphere.
They are separated from each other by using coconut charcoal at different temperatures.
Coconut charcoal acts as an adsorbent that selectively adsorbs different noble gases at different temperatures.

(C) The correct answer is $(C)$.
At low temperatures like $100 \ K$,coconut charcoal acts as an adsorbent for noble gases.
Except for $He$,all other noble gases are adsorbed by coconut charcoal.
The extent of adsorption increases with an increase in the atomic size and polarizability of the noble gas.
Therefore,$Ar$,$Kr$,and $Xe$ are adsorbed,while $He$ and $Ne$ are adsorbed to a negligible extent.

(C) When $AgNO_3$ is added in excess to $KI$ solution,the $AgI$ precipitate formed adsorbs $Ag^{+}$ ions from the dispersion medium.
This results in the formation of a positively charged colloidal sol of $AgI$.

(B) . Chemisorption is irreversible in nature because it involves the formation of strong chemical bonds between the adsorbent and the adsorbate.

(A) Chemisorption involves the formation of chemical bonds between the adsorbate and the adsorbent.
This process requires an activation energy to initiate the bond formation.
Therefore,initially,chemisorption increases with an increase in temperature as more molecules gain sufficient energy to overcome the activation barrier.

(B) Adsorption is a surface phenomenon that depends on the surface area of the adsorbent.
$1$. The adsorption process can be monolayered (chemisorption) or multilayered (physisorption).
$2$. The particle size of the adsorbent significantly affects the amount of adsorption. Smaller particle size leads to a larger surface area,which increases the amount of adsorption. Therefore,the statement that particle size does not affect adsorption is false.
$3$. According to Le Chatelier's principle,since physical adsorption is an exothermic process,an increase in temperature decreases the amount of adsorption.
$4$. An increase in pressure generally increases the amount of gas adsorbed on a solid surface.

(A) Wood charcoal is used to decolorize sugar because it has a highly porous structure,providing a large surface area for adsorption.
Therefore,it adsorbs coloured material from sugar.

(A) The adsorption in which molecules of adsorbate are held on the surface of an adsorbent by Van der Waals forces or weak physical forces is called physical adsorption,Van der Waals adsorption,or physisorption.

(C) solid acts as an adsorbent because of the presence of unsaturated valencies on its surface.
These residual forces or unsaturated valencies attract and retain the molecules of a gas or liquid on the surface of the solid.
Activated charcoal is a common example of a good adsorbent due to its large surface area and high number of available unsaturated valencies.

(B) The characteristics of physical adsorption $(Physisorption)$ are:
$1$. It is not specific in nature.
$2$. It is a reversible process.
$3$. It results in multimolecular adsorption layers.
$4$. It depends on the nature of the gas; more easily liquefiable gases are adsorbed readily.
$5$. The enthalpy of adsorption is low $(20-40 \ kJ \ mol^{-1})$.
$6$. Low temperature is favorable for adsorption,meaning adsorption decreases with an increase in temperature.
$7$. There is no requirement for activation energy.
$8$. It depends on the surface area; hence,porous surfaces are good adsorbents.
Therefore,the statement that physical adsorption is irreversible is incorrect.

(B) Adsorption is an exothermic process. According to Le Chatelier's principle,lowering the temperature shifts the equilibrium in the forward direction,which increases the adsorption of gas on a solid surface.
Increasing the pressure forces more gas molecules to come into contact with the solid surface,thereby increasing the extent of adsorption.

(D) In physisorption,the enthalpy of adsorption is very low because the accumulation of substances on the surface is due to $Van \ der \ Waal's$ forces,which are weak in nature.

(A) Adsorption is multilayer in the case of physical adsorption (physisorption) due to weak van der Waals forces.
In contrast,chemisorption is unilayer because it involves the formation of strong chemical bonds between the adsorbate and adsorbent molecules.

(A) Physical adsorption (physisorption) is characterized by weak van der Waal's forces between the adsorbent and adsorbate.
It is reversible,non-specific,and multi-layered.
Since it is an exothermic process,it decreases with an increase in temperature.

(D) In the process of adsorption,the substance that gets adsorbed on the surface of another substance is called the $Adsorbate$.
In this case,acetic acid is the substance that accumulates on the surface of the activated charcoal.
Therefore,acetic acid is the $Adsorbate$ and activated charcoal is the $Adsorbent$.

(C) The phenomenon of accumulation of molecular species at the surface rather than in the bulk of a solid or liquid is known as $Adsorption$.

(D) The extent of adsorption has an upper limit because it depends upon other factors too,such as pressure,temperature,and the nature of the adsorbent and adsorbate. As the surface area of the adsorbent is finite,the adsorption process reaches a saturation point.

(D) The Freundlich adsorption isotherm is given by the equation: $\frac{x}{m} = kp^{1/n}$.
Taking the logarithm on both sides,we get: $\log(x/m) = \log k + \frac{1}{n} \log p$.
Comparing this with the linear equation $y = mx + c$,where $y = \log(x/m)$,$x = \log p$,$m = \text{slope} = 1/n$,and $c = \text{intercept} = \log k$.
Therefore,the slope of the plot of $\log(x/m)$ versus $\log p$ is $1/n$.

(A) The Langmuir adsorption isotherm equation is given by $x/m = (aP) / (1 + bP)$.
At very high pressures,the term $bP$ becomes much larger than $1$,so the equation simplifies to $x/m = (aP) / (bP) = a/b$.
Since $a$ and $b$ are constants,the amount of gas adsorbed $(x/m)$ reaches a constant limiting value.

(B) Chemisorption involves high activation energy. Therefore,it initially increases with temperature as the heat supplied acts as activation energy. However,at higher temperatures,it decreases due to the exothermic nature of the adsorption process at equilibrium. Option $B$ is incorrect because chemical adsorption typically increases with temperature initially due to activation energy requirements,unlike physical adsorption which decreases with temperature.

(A) In the process of adsorption,the substance on whose surface the adsorption takes place is called the $Adsorbent$.
In this case,oxalic acid is the substance being adsorbed $(Adsorbate)$,and activated charcoal is the surface on which it gets adsorbed $(Adsorbent)$.
Therefore,the correct option is $(A)$.

(C) Adsorption is the phenomenon in which a substance accumulates on the surface of another substance.
Thus,it is a surface phenomenon.

(C) Physical adsorption is an exothermic process,where the enthalpy change $(\Delta H)$ is negative.
According to Le Chatelier's principle,for an exothermic process,the extent of adsorption decreases with an increase in temperature.
Therefore,physical adsorption is more significant and appreciable at lower temperatures.

(B) Adsorption is an exothermic process. According to Le Chatelier's principle,for an exothermic process,the extent of adsorption increases when the temperature decreases. Mathematically,the relationship is expressed as $\text{Adsorption} \propto \frac{1}{T}$.

(A) In chemical adsorption,a chemical bond is formed between the adsorbate and the adsorbent. This process is specific and leads to the formation of a unimolecular layer. Therefore,only $1$ layer is adsorbed.

(A) According to the Freundlich adsorption isotherm,the adsorption of a gas on a solid surface follows these stages with increasing pressure:
$1$. At low pressure,the extent of adsorption $(x/m)$ is directly proportional to pressure $(P^1)$,which is a fast process.
$2$. At intermediate pressure,it is proportional to $P^{1/n}$ (where $n > 1$),showing a slower rate of increase.
$3$. At high pressure,the surface becomes saturated,and adsorption becomes independent of pressure $(P^0)$.
Thus,the correct sequence is: Fast $\to$ slow $\to$ independent of the pressure.

(D) Chemisorption is a chemical process that involves the formation of chemical bonds between the adsorbate and the adsorbent.
It is highly specific,irreversible,and generally slow.
Unlike physisorption,chemisorption is dependent on temperature; it typically increases with an increase in temperature initially due to the activation energy required for bond formation and may decrease at higher temperatures.
Therefore,the statement that it is independent of temperature is incorrect.

(B) Adsorption is a surface phenomenon where the residual forces of the surface decrease,leading to the release of energy. Thus,adsorption is always an exothermic process,meaning $\Delta H < 0$.

(C) The adsorption of gases on solid surfaces is known as adsorption.
Transition metals like $Pt$,$Pd$,and $Ni$ are known to adsorb hydrogen gas very strongly on their surfaces.
Among the given options,$Platinum \text{ } black$ (finely divided platinum) has a very large surface area and exhibits the highest capacity to adsorb hydrogen gas,making it an effective catalyst for hydrogenation reactions.

(D) The Freundlich adsorption isotherm is given by the equation $\frac{x}{m} = kP^{1/n}$,where $x$ is the mass of the adsorbate,$m$ is the mass of the adsorbent,$P$ is the pressure,and $k$ and $n$ are constants depending on the nature of the adsorbent and the gas at a particular temperature.
From this equation,it is clear that the extent of adsorption $\frac{x}{m}$ is proportional to $P^{1/n}$.

(B) Physical adsorption is an exothermic process. According to Le Chatelier's Principle,for an exothermic process,an increase in temperature favors the reverse process (desorption). Therefore,physical adsorption decreases with an increase in temperature.
For a process to be spontaneous,the Gibbs free energy change $\Delta G$ must be negative. Since $\Delta G = \Delta H - T\Delta S$,and adsorption involves a decrease in entropy $(\Delta S < 0)$,the process can only be spontaneous if $\Delta H$ is negative (exothermic) and the temperature $T$ is low enough such that $|\Delta H| > |T\Delta S|$.

(C) Chemisorption involves the formation of chemical bonds,which leads to the formation of a unimolecular layer.
In contrast,physisorption involves weak van der Waals forces,which can lead to the formation of a multimolecular layer.
Therefore,the statement that chemisorption may be a multimolecular layer is incorrect.

(A) Adsorption due to strong chemical forces is known as chemical adsorption or $ \text{Chemisorption} $.
In this process,the adsorbate molecules are held to the surface of the adsorbent by strong chemical bonds.

(A) When $KI$ is added to $AgNO_3$ in slight excess,the $AgI$ colloidal particles adsorb $Ag^{+}$ ions from the dispersion medium,resulting in a positively charged sol.
Thus,the positive charge is due to the adsorption of $Ag^{+}$ ions.

(C) Physical adsorption is an exothermic process. According to Le Chatelier's principle,an increase in temperature shifts the equilibrium in the backward direction,thereby decreasing the extent of adsorption. Thus,physical adsorption is inversely proportional to the $Temperature$.

(C) The initial moles of oxalic acid $= M_1 \times V = 1 \ M \times 0.05 \ L = 0.05 \ mol$.
The final moles of oxalic acid $= M_2 \times V = 0.5 \ M \times 0.05 \ L = 0.025 \ mol$.
The moles of oxalic acid adsorbed $= 0.05 - 0.025 = 0.025 \ mol$.
The molar mass of oxalic acid $(H_2C_2O_4 \cdot 2H_2O)$ is $126 \ g/mol$.
The mass of oxalic acid adsorbed by $0.5 \ g$ of charcoal $= 0.025 \ mol \times 126 \ g/mol = 3.15 \ g$.
Therefore,the amount of oxalic acid adsorbed per $g$ of charcoal $= \frac{3.15 \ g}{0.5 \ g} = 6.30 \ g/g$.

(D) Noble gases are adsorbed by activated coconut charcoal.
The adsorption of different noble gases occurs at different temperatures,which allows coconut charcoal to be used for the separation of these gases.
Helium is not significantly adsorbed by charcoal because it is a very difficult gas to liquefy due to its extremely weak van der Waals forces.

(B) Animal charcoal acts as a good adsorbent.
It removes the coloured impurities from liquids by adsorbing them onto its surface,thereby decolourising the liquid.

(A) The correct answer is $(A)$.
Since physical adsorption is an exothermic process (involving the evolution of heat),according to Le Chatelier's principle,the magnitude of adsorption decreases as the temperature increases.
In contrast,for chemisorption,the rate of adsorption typically increases initially due to the activation energy requirement and then decreases at higher temperatures.

(C) The correct answer is $(C)$.
Animal charcoal acts as an adsorbent.
When it is added to an acetic acid solution,the acetic acid molecules get adsorbed on the surface of the charcoal.
Due to this adsorption,the number of acetic acid molecules in the bulk solution decreases,leading to a decrease in the concentration of the solution.

(D) The Freundlich adsorption isotherm is generally expressed as $\frac{x}{m} = k{p^{1/n}}$,where $x$ is the mass of the adsorbate,$m$ is the mass of the adsorbent,$p$ is the pressure,and $k$ and $n$ are constants.
By rearranging this,we get $x = m \cdot k{p^{1/n}}$.
While the standard form is $\frac{x}{m} = k{p^{1/n}}$,the other expressions are mathematically equivalent representations of the same relationship.
Therefore,all of these equations represent the Freundlich adsorption isotherm.

(D) The extent of adsorption of a gas on a solid depends on several factors:
$1$. Nature of the gas (adsorbate): Easily liquefiable gases are adsorbed more readily than gases that do not liquefy easily.
$2$. Pressure of the gas: With an increase in pressure,the extent of adsorption increases.
$3$. Temperature of the gas: An increase in temperature decreases the extent of adsorption because physical adsorption is an exothermic process.
$4$. Nature and surface area of the adsorbent: $A$ greater surface area of the adsorbent leads to a greater extent of adsorption.
Since all the given options ($A$,$B$,and $C$) are factors that influence the extent of adsorption,the correct option is $D$.

(D) $($ $d$ $)$ It has been observed that the surface of a solid (or liquid) has the tendency to attract and retain the molecules of other immiscible phase with which it is brought into contact.
These molecules remain only at the surface and do not go deeper into the bulk.
This tendency of accumulation of molecular species at the surface rather than in the bulk of a solid (or liquid) is termed adsorption.

(B) The Freundlich adsorption isotherm is given by the empirical relation: $\frac{x}{m} = K P^{1/n}$,where $x$ is the mass of the adsorbate,$m$ is the mass of the adsorbent,$P$ is the pressure,and $K$ and $n$ are constants depending on the nature of the adsorbent and adsorbate at a particular temperature. Taking the logarithm on both sides,we get: $\log \frac{x}{m} = \log K + \frac{1}{n} \log P$. Among the given options,option $B$ represents the standard form of the Freundlich adsorption isotherm.

(C) Physisorption is a process in which the particles of adsorbate are held to the surface of adsorbent by physical forces (van der Waals forces).
Because these forces are weak,physisorption does not require any significant activation energy,unlike chemisorption.

(B) The extent of adsorption of a gas on a solid adsorbent like activated charcoal depends on the ease of liquefaction of the gas.
Easily liquefiable gases have higher critical temperatures and stronger van der Waals forces of attraction,leading to greater adsorption.
Among the given options,$SO_2$ is the most easily liquefiable gas compared to $N_2, H_2,$ and $O_2$.
Therefore,$SO_2$ is readily adsorbed by activated charcoal.