Colloids, Emulsion, Gel and Their properties with application Questions in English

(A) . Dialysis is a process used for the purification of colloidal solutions by removing electrolytes through a semi-permeable membrane.
$B$. Peptization is the process of converting a freshly prepared precipitate into a colloidal sol by adding a suitable electrolyte.
$C$. Emulsification is the process of stabilizing an emulsion,which is the principle behind the cleansing action of soap.
$D$. Electrophoresis is the movement of colloidal particles under an applied electric field,which leads to their coagulation at the electrodes.
Therefore,the correct matching is $A-d, B-c, C-a, D-b$.

(B) The Sol-Gel process is a chemical solution deposition technique used to produce solid materials from small molecules.
It involves two primary sequential steps:
$1$. Hydrolysis: The precursor (usually a metal alkoxide) reacts with water to form hydroxyl groups.
$2$. Polycondensation: These hydroxyl groups then undergo condensation reactions to form a network of metal-oxygen-metal bonds $(M-O-M)$,leading to the formation of a gel.

(A) delta is formed where a river meets the sea due to the process of settling down of colloidal particles. The river water contains colloidal clay particles,while sea water contains various electrolytes. When these two meet,the electrolytes present in sea water cause the coagulation of the colloidal clay particles,leading to their deposition and the formation of a delta.

(C) In $Cottrell's$ precipitator,the charged colloidal particles are attracted towards the oppositely charged plates (walls of the precipitator).
Upon contact,they lose their charge and undergo coagulation.
Hence,the basic principle of $Cottrell's$ precipitator is the neutralisation of charge on colloidal particles.

(A) The function of $Fe(OH)_{3}$ in the contact process is to remove arsenic impurity.
$Fe(OH)_{3}$ is a positive sol,hence it removes arsenic impurity which is a negative sol.

(A) When $FeCl_3$ is added to an excess of hot water,hydrolysis occurs to form a positively charged sol '$X$' of hydrated ferric oxide,which adsorbs $Fe^{3+}$ ions from the solution: $Fe_2O_3 \cdot xH_2O / Fe^{3+}$.
When $FeCl_3$ is added to $NaOH_{(aq)}$ solution,the resulting hydrated ferric oxide sol adsorbs $OH^{-}$ ions from the excess $NaOH$ to form a negatively charged sol '$Y$': $Fe_2O_3 \cdot xH_2O / OH^{-}$.

(B) Silver iodide $(AgI)$ has a crystal structure similar to that of ice.
Due to this structural similarity,it acts as an effective nucleating agent for water droplets in clouds.
This procedure is known as 'Cloud seeding' and is used to induce artificial rain.

(C) Gold sol is a colloidal suspension of gold nanoparticles in a liquid.
It is a lyophobic colloid because there is no affinity between the dispersed phase and the dispersion medium.
It is negatively charged due to the adsorption of $OH^-$ ions.
It is a multimolecular colloid because it consists of aggregates of a large number of atoms or smaller molecules with diameters less than $1 \ nm$.

(A) The $AgI/Ag^{+}$ sol is a positively charged sol.
According to the Hardy-Schulze rule,the flocculation power of an electrolyte depends on the valency of the coagulating ion (the ion with a charge opposite to that of the sol).
For a positively charged sol,the coagulating power increases with the increase in the negative charge of the anion: $Cl^{-} < SO_{4}^{2-} < PO_{4}^{3-}$.
Flocculation value is inversely proportional to flocculation power.
Since $Cl^{-}$ has the minimum flocculation power,$NaCl$ will have the maximum flocculation value.

(C) sol is a colloidal system where solid particles are dispersed in a liquid medium. Sulphur sol is a lyophobic colloid formed by the aggregation of a large number of $S_8$ molecules. Therefore,it contains large aggregates of $S$ molecules.

(A) Colloidal particles are larger aggregates compared to solute particles in a true solution.
Since the number of particles in a colloidal dispersion is significantly smaller than in a true solution at the same concentration,the colligative properties,such as osmotic pressure,are of a low order.
Therefore,colloidal dispersions exhibit low osmotic pressure.

(D) The reaction between $AgNO_{3}$ and $KI$ is: $AgNO_{3} + KI \longrightarrow AgI(s) + KNO_{3}$.
Since equal volumes are mixed,the number of moles of $KI$ $(0.2 \ M)$ is greater than the number of moles of $AgNO_{3}$ $(0.1 \ M)$.
Thus,$KI$ is in excess.
The $AgI$ particles preferentially adsorb the common ion present in excess from the dispersion medium.
In this case,$I^{-}$ ions are in excess and are adsorbed on the surface of $AgI$ particles,resulting in a negatively charged sol.

(A) Gold sols are formed by the aggregation of a large number of gold atoms,making them $multimolecular$ colloids.
They are $lyophobic$ in nature and carry a $negative$ charge due to the adsorption of $OH^-$ ions.
They are not $macromolecular$ colloids,as macromolecular colloids consist of large molecules like proteins or starch.

(A) Since the colloidal particles move towards the anode,they are negatively charged.
According to the Hardy-Schulze rule,the coagulating power of an electrolyte increases with the increase in the magnitude of the charge on the cation (for negatively charged colloids).
The coagulating power order is $Al^{3+} > Ba^{2+} > Na^{+}$.
Since the coagulation value is inversely proportional to the coagulating power,the amount of electrolyte required follows the order: $NaCl > BaCl_{2} > AlCl_{3}$.

(D) The $AgI / Ag^{+}$ sol is a positively charged sol. According to the Hardy-Schulze rule,the coagulating power of an electrolyte depends on the valency of the oppositely charged ion (anion in this case).
Greater the valency of the flocculating ion,greater is its coagulating power.
Coagulating power is inversely proportional to the coagulating value.
The valency of the anions are: $PO_{4}^{3-} (3) > SO_{4}^{2-} (2) = S^{2-} (2) > Cl^{-} (1)$.
Since $Cl^{-}$ has the lowest valency,it has the minimum coagulating power and therefore the maximum coagulating value.

(C) Gold sol is a $multimolecular$ colloid because it consists of aggregates of a large number of gold atoms $(Au_n)$ with diameters less than $1 \ nm$. It is a $lyophobic$ sol and is $negatively$ charged. It is not a $macromolecular$ colloid,as macromolecular colloids are formed by large molecules like starch or proteins.

(C) Macromolecular colloids are quite stable and resemble true solutions in many respects.
Due to their high stability and the presence of a solvation layer,they cannot be easily coagulated compared to lyophobic colloids.

(C) The stability of a lyophobic colloidal solution is primarily due to the presence of electrical charges on the colloidal particles.
Because all particles carry the same type of charge (either positive or negative),they repel each other.
This electrostatic repulsion prevents the particles from coming close enough to coalesce and settle down,thereby maintaining the stability of the colloid.

(C) Hydrophobic sols are irreversible in nature.
They have no affinity between the dispersed phase and the dispersion medium $(H_{2}O)$.
Once precipitated,they do not form the colloidal sol by simple addition of water.

(C) The correct option is $C$.
Micelles are formed only when the concentration of the surfactant (soap) in the solution is greater than the $CMC$ value.
Given $CMC = 1.5 \times 10^{-4} \ mol \ L^{-1}$.
Comparing the given options,only $2.0 \times 10^{-3} \ mol \ L^{-1}$ is greater than $1.5 \times 10^{-4} \ mol \ L^{-1}$.

(B) Dialysis is a process used to separate colloidal particles from crystalloids through a semi-permeable membrane.
Colloidal particles (like proteins) cannot pass through the membrane,while crystalloids (like glucose) can pass through.
Therefore,dialysis is used to separate $glucose$ and $protein$.

(D) The incorrect statement is given in option $(D)$.
Brownian movement is caused by the unbalanced bombardment of molecules of the dispersion medium on the colloidal particles,which results in a zig-zag motion.
Therefore,the statement claiming it is due to balanced bombardment is incorrect.

(D) According to the $Hardy-Schulze$ rule,the coagulating (or flocculating) power of an ion depends on its valency.
For a positively charged sol,the coagulating power of the anions increases with the increase in the magnitude of their negative charge.
The valencies of the given ions are: $[Fe(CN)_6]^{4-}$ $(4-)$,$PO_4^{3-}$ $(3-)$,$SO_4^{2-}$ $(2-)$,and $Cl^{-}$ $(1-)$.
Therefore,the order of flocculating power is $[Fe(CN)_6]^{4-} > PO_4^{3-} > SO_4^{2-} > Cl^{-}$.

(D) Among the given options,colloidal sulphur is commonly used in the treatment of skin diseases,often in the form of lotions or ointments to treat conditions like acne or scabies.

(C) Zeta potential,also known as electrokinetic potential,is the potential difference between the fixed charged layer and the diffused layer of opposite charges surrounding the colloidal particle.

(D) The minimum amount of an electrolyte that must be added to one litre of a colloidal solution to bring about complete coagulation is called the coagulation or flocculation value of the electrolyte.
According to the Hardy-Schulze rule,the greater the valency of the coagulating or flocculating ion,the smaller the quantity of the electrolyte required to coagulate a definite amount of the colloidal sol.
Arsenic sulphide sol is a negatively charged sol.
Therefore,it is coagulated by cations.
The effectiveness of cations follows the order: $Al^{3+} > Ca^{2+} = Mg^{2+} > Na^{+}$.
Since the flocculation value is inversely proportional to the coagulating power,the order of flocculation value is: $Na^{+} > Ca^{2+} = Mg^{2+} > Al^{3+}$.
Thus,$Al^{3+}$ has the minimum flocculation value.

(D) Coagulation is the process of aggregating colloidal particles to form a precipitate.
$A$,$B$,and $C$ involve the aggregation of particles (coagulation).
Peptization is the reverse process,where a freshly prepared precipitate is converted into a colloidal sol by adding a suitable electrolyte (peptizing agent).
Therefore,peptization does not involve coagulation.

(B) The blue colour of the sky is due to the $Tyndall$ effect. The colloidal particles present in the atmosphere scatter light of different wavelengths in all possible directions. According to $Rayleigh$ scattering,the intensity of scattered light is inversely proportional to the fourth power of its wavelength $(I \propto 1/\lambda^4)$. Since blue light has a shorter wavelength,it is scattered more strongly than other colours.

(C) In electro-osmosis,the movement of the dispersed phase is prevented by a semi-permeable membrane,and the dispersion medium moves under the influence of an electric field.
Since $Fe(OH)_3$ sol is positively charged,the dispersion medium is negatively charged.
Therefore,the dispersion medium moves towards the anode.

(B) The correct answer is $B$.
Gold sol is a lyophobic sol,not a lyophilic sol.
Milk is a natural emulsion of fat in water.
Physical adsorption (physisorption) is exothermic and decreases with an increase in temperature.
Chemical adsorption (chemisorption) is specific and forms a unilayer (monolayer) on the surface.

(D) $I$) Sulphur sol consists of a large number of $S_8$ molecules aggregated together,hence it is a multimolecular colloid. This statement is correct.
$II$) Starch sol is a macromolecular colloid because starch molecules are naturally occurring polymers with high molecular masses. It is not an associated colloid (micelle). This statement is incorrect.
$III$) Artificial rubber is a synthetic polymer with a high molecular mass,making it a macromolecular colloid. This statement is correct.
Therefore,statements $I$ and $III$ are correct.

(B) colloidal system in which both the dispersed phase and the dispersion medium are liquids is known as an $emulsion$.
Examples include milk and butter.

(B) The applications of various colloidal solutions in medicine are as follows:
$1$. Colloidal antimony is used in the treatment of $Kala-azar$.
$2$. Argyrol is a silver sol used as an eye lotion.
$3$. Colloidal gold is used for intramuscular injection.
$4$. Milk of magnesia is used for stomach disorders.
Therefore,the correct matching is $A-I, B-II, C-III, D-IV$.

(D) The correct answer is $D$.
An aerosol is a colloidal system in which a solid or liquid is dispersed in a gas.
Option $A$ is correct as colloidal particles exhibit Brownian motion and the Tyndall effect.
Option $B$ is correct as the Hardy-Schulze rule describes the coagulation of sols by electrolytes.
Option $C$ is correct as the gold number is a measure of the protective power of a lyophilic colloid.
Option $D$ is incorrect because in an aerosol,the dispersion medium is a gas,not the dispersed phase.

(C) The preparation methods for various colloidal sols are as follows:
$A$. $As_2S_3$ (Arsenic sulfide) sol is prepared by double decomposition: $As_2O_3 + 3H_2S \rightarrow As_2S_3 + 3H_2O$.
$B$. $Au$ (Gold) sol is prepared by Bredig's arc method (dispersion method).
$C$. $S$ (Sulfur) sol is prepared by oxidation: $2H_2S + SO_2 \rightarrow 3S + 2H_2O$.
$D$. $Fe(OH)_3$ (Ferric hydroxide) sol is prepared by hydrolysis: $FeCl_3 + 3H_2O \rightarrow Fe(OH)_3 + 3HCl$.
Thus,the correct matching is $A-IV, B-I, C-II, D-III$.

(D) The critical micelle concentration $(CMC)$ is the concentration above which the formation of micelles occurs in a colloidal system.
$I$. At a concentration of $10^{-7} \ mol \ L^{-1}$,which is less than the $CMC$ $(5 \times 10^{-4} \ mol \ L^{-1})$,the soap molecules exist as individual ions or molecules in the solution,not as micelles. Thus,this statement is incorrect.
$II$. Micelles are formed and are stable only when the concentration of the soap solution is equal to or higher than the $CMC$. Thus,this statement is correct.
$III$. Micelles are indeed classified as associated colloids because they are aggregates of molecules that behave as colloidal particles at higher concentrations. Thus,this statement is correct.
Therefore,statements $II$ and $III$ are correct.

(D) Colloidal gold sol is used as an intramuscular injection.
Colloidal gold generally has a much larger surface area,which results in very easy and smooth assimilation in the body.
Gold sol is considered to be much more effective and it is non-toxic.
It possesses several therapeutic benefits.

(A) The correct matches are as follows:
$I$. Colloidal antimony is used for the treatment of Kala-azar $(A)$.
$II$. Silver sol is used as an eye lotion $(C)$.
$III$. Milk of magnesia is used to treat stomach disorders $(D)$.
$IV$. Gold sol is used for intramuscular injections $(B)$.
Therefore,the correct sequence is $I-A, II-C, III-D, IV-B$.

(C) According to the $Hardy-Schulze$ rule,the coagulating power of an electrolyte is directly proportional to the valency of the active ion (ion with charge opposite to that of the sol).
Antimony sulphide $(Sb_2S_3)$ sol is a negatively charged sol.
Therefore,it requires a positively charged ion for coagulation.
The coagulating power increases with the increase in the magnitude of the charge on the cation.
The cations present in the given options are: $K^+$ $(+1)$,$NH_4^+$ $(+1)$,$Al^{3+}$ $(+3)$,and $K^+$ $(+1)$.
Since $Al^{3+}$ has the highest valency $(+3)$,$Al_2(SO_4)_3$ is the most effective coagulating agent.

(A) Multi-molecular colloids are formed by the aggregation of a large number of atoms or small molecules with diameters less than $1 \ nm$.
Sulphur sol is a classic example of a multi-molecular colloid,where a large number of $S_8$ molecules aggregate to form particles of colloidal size.

(C) Starch sol is a negatively-charged sol,whereas $TiO_2$ sol is a positively-charged sol.
Therefore,the matches in $II$ (Starch sol; $+ve$ sol) and $III$ ($TiO_2$ sol; $-ve$ sol) are incorrect.

(B) In the given reaction,the oxidation state of gold $(Au)$ changes from $+3$ in $AuCl_3$ to $0$ in elemental $Au$.
Since the oxidation state decreases,this process is a reduction reaction.
Thus,the preparation of gold sol involves the reduction of gold ions.

(A) The Tyndall effect is the phenomenon of scattering of light by colloidal particles.
For this effect to be observed,the size of the dispersed particles must be comparable to or not much smaller than the wavelength of the light used.
Therefore,both statement $S-I$ and statement $S-II$ are correct.

(B) The classification of colloids based on the dispersed phase and dispersion medium is as follows:
$(A)$ Solid in liquid is called a Sol $(III)$.
$(B)$ Liquid in liquid is called an Emulsion $(IV)$.
$(C)$ Solid in gas is called an Aerosol $(II)$.
$(D)$ Liquid in solid is called a Gel $(I)$.
Therefore,the correct matching is: $A-III, B-IV, C-II, D-I$.

(B) Gold $(Au)$ sol is formed by the aggregation of a large number of atoms,making it a multimolecular colloid.
It is a lyophobic (solvent-fearing) sol,as it does not have a strong affinity for the dispersion medium.
Gold sol particles are negatively charged due to the preferential adsorption of anions (like $OH^-$) on their surface.
Therefore,statements $(II)$,$(III)$,and $(IV)$ are correct.

(A) colloid is a heterogeneous system in which one substance is dispersed (dispersed phase) as very fine particles in another substance called the dispersion medium.
The essential difference between a true solution and a colloid is the particle size.
In a true solution,the constituent particles are ions or small molecules.
In a colloid,the dispersed phase consists of particles of a single macromolecule or an aggregate of many atoms,ions,or molecules.
Colloidal particles are larger than simple molecules but small enough to remain suspended.
Their range of diameters is between $1 \ nm$ and $1000 \ nm$ ($10^{-9} \ m$ to $10^{-6} \ m$).

(D) Macromolecules in suitable solvents form solutions in which the size of the macromolecules may be in the colloidal range. Such systems are called macromolecular colloids.
These colloids are quite stable and resemble true solutions in many respects.
Examples of naturally occurring macromolecules are starch,cellulose,proteins,and enzymes.
Examples of man-made macromolecules are polythene,nylon,polystyrene,synthetic rubber,etc.
Therefore,$I$ (Starch solution) and $IV$ (Synthetic rubber) are examples of macromolecular colloids.
$II$ (Sulphur sol) is a multimolecular colloid,and $III$ (Synthetic detergent) is an associated colloid (micelle).