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

(A) The process by which suspended particles in a fluid settle down under the influence of gravity is known as $Sedimentation$. In the context of colloidal chemistry,when particles aggregate and settle due to the addition of an electrolyte,it is often referred to as $Coagulation$ or $Flocculation$. However,the general term for particles settling on the floor of a chamber is $Sedimentation$.

(N/A) Argyrol is a $silver$ sol,which is a type of colloidal solution where $silver$ particles are dispersed in a protein medium.
It is primarily used as an antiseptic in eye drops and for treating infections in mucous membranes.

(A) Latex is a colloidal dispersion of rubber particles in water.
When latex is coagulated,typically by the addition of an acid like acetic acid or formic acid,the rubber particles aggregate to form a solid mass known as $Rubber$.

(N/A) Schulze and Hardy observed that 'the greater the valency of the flocculating ion added,the greater is its power to cause precipitation.' This rule considers only the charge on the ion,not its size. The smaller the size of the ion,the greater is its polarising power. Thus,the Hardy-Schulze rule can be improved as follows: 'The greater the polarising power of the added flocculating ion,the greater is its precipitating power.'

(C) Soap at a lower concentration behaves as an electrolyte,forming a true solution.
However,if the concentration exceeds the $CMC$ (Critical Micelle Concentration),the soap molecules aggregate to form a micelle,which behaves like a colloidal solution.

(B) Gelatin is a lyophilic colloid. When added to a lyophobic sol like gold sol,it forms a protective layer around the gold particles,thereby preventing their coagulation by electrolytes. This process is known as the stabilization of the sol.

(B) Clouds are colloidal systems consisting of charged water droplets dispersed in air.
When $AgI$ (silver iodide) is sprayed over the clouds,it acts as an electrolyte.
This causes the coagulation of the charged colloidal water droplets,leading to the formation of larger droplets that fall as artificial rain.

(B) Gelatin is a protein (peptide) that acts as a stabilizer or emulsifying agent in ice creams.
It prevents the formation of large ice crystals,thereby maintaining the smooth texture of the ice cream.

(N/A) Water often contains negatively charged colloidal impurities. When alum $(K_2SO_4 \cdot Al_2(SO_4)_3 \cdot 24H_2O)$ is added to water,it dissociates to provide $Al^{3+}$ ions. These $Al^{3+}$ ions neutralize the charge on the colloidal particles,leading to their coagulation. The coagulated impurities settle down at the bottom and can be removed by filtration,resulting in purified water.

(A) Colloidal particles carry a specific electric charge (either positive or negative).
When an electric field is applied,these particles migrate towards the electrode with the opposite charge.
This phenomenon is known as $electrophoresis$.

(N/A) Brownian motion is caused by the unbalanced bombardment of the colloidal particles by the molecules of the dispersion medium. These molecules are in constant,rapid motion,similar to molecules in a gas. As a result of these collisions,the colloidal particles acquire kinetic energy comparable to that of the dispersion medium molecules,leading to their characteristic zig-zag motion.

(B) Adding excess $FeCl_3$ to hot water produces a colloidal solution of hydrated ferric oxide,$Fe_2O_3 \cdot xH_2O$,which is a positively charged colloid.
When excess $NaCl$ is added,the $Cl^-$ ions from the electrolyte neutralize the positive charge on the colloidal particles.
This process leads to the coagulation of the colloidal sol.

(B) Emulsifying agents stabilize emulsions by forming an interfacial film between the suspended particles and the dispersion medium.
This film reduces the interfacial tension between the two immiscible liquids,thereby preventing the coalescence of droplets and maintaining the stability of the emulsion.

(N/A) Colloidal medicines are more effective because they have a large surface area and are therefore more easily assimilated by the body.
For example: Colloidal gold is used for intramuscular injection,and silver sol is used as an eye lotion.

(N/A) Animal hides are colloidal in nature. When a hide that has positively charged particles is soaked in tannin,the negatively charged colloidal particles undergo mutual coagulation. This results in the hardening of leather. This process is known as Tanning.

(N/A) The Cottrell precipitator is a device used to remove smoke from industrial gases.
Smoke is a colloidal dispersion of solid carbon particles in air.
These colloidal particles are electrically charged.
In the Cottrell precipitator,the smoke is passed through a chamber containing metal plates connected to a high-voltage source.
These plates act as electrodes.
When the smoke passes between these charged plates,the colloidal particles lose their charge upon coming in contact with the oppositely charged electrode.
Once the charge is neutralized,the particles aggregate and settle down due to gravity,leaving the clean gas to escape.

(N/A) An emulsion can be diluted with any amount of the dispersion medium. However,if the dispersed phase is added,it will not mix and will form a separate layer. Thus,by adding the dispersion medium to the emulsion,the two phases can be distinguished.

(N/A) According to the Hardy-Schulze rule,the coagulating power of an ion is directly proportional to its valency (charge).
$PO_{4}^{3-}$ has a valency of $3$,whereas $Cl^-$ has a valency of $1$.
Since the valency of the phosphate ion $(3)$ is greater than that of the chloride ion $(1)$,the coagulating power of phosphate is higher than that of chloride.

(B) Alum is a salt containing $Al^{3+}$ ions. When applied to a wound,these $Al^{3+}$ ions neutralize the negatively charged colloidal particles of blood. This process leads to the coagulation of blood,which helps in stopping the bleeding.

(N/A) The electrolytes present in the colloidal solution help in stabilizing the sol particles. On prolonged dialysis,these traces of electrolytes are removed completely from the solution. As a result,the stability of the colloidal system is lost,which leads to the coagulation of the sol particles.

(N/A) River water contains colloidal particles of mud and clay,which carry a negative charge. Sea water contains various electrolytes such as $NaCl$ and $MgCl_2$. When river water meets sea water,the electrolytes present in the sea water neutralize the charge on the colloidal particles of mud and clay. This process is known as coagulation or flocculation. As a result,the mud and clay particles settle down at the river mouth,leading to the formation of a delta.

(N/A) Sodium lauryl sulphate,$CH_3(CH_2)_{10}CH_2OSO_3Na$,is an example of an anionic detergent.
When added to water,it dissociates as follows:
$CH_3(CH_2)_{10}CH_2OSO_3Na + H_2O \longrightarrow CH_3(CH_2)_{10}CH_2OSO_3^- + Na^+ + H_2O$
These anions are present on the surface with their $-OSO_3^-$ groups in water and the hydrocarbon part staying away from it,remaining at the surface.
At higher concentration,these anions are pulled into the bulk of the solution and form an aggregate of spherical shape with their hydrocarbon part pointing towards the centre and the $-OSO_3^-$ part outwards on the surface of the sphere.

(B) Adding oil to the paint reduces its surface tension.
Due to lower surface tension,the paint spreads over a larger surface area.
As a result,less paint is required to cover a larger area,making the process more economical.

(C) Bredig's Arc method is a specialized technique used for the preparation of colloidal solutions of metals like $Au$,$Ag$,and $Pt$.

(A) An ionic micelle is a colloidal aggregate formed by amphiphilic molecules (surfactants) in a polar solvent,typically water,when their concentration exceeds the Critical Micelle Concentration $(CMC)$.
Sodium stearate $(C_{17}H_{35}COONa)$ is a soap,which is an ionic surfactant.
When added to water,the hydrophobic hydrocarbon tails aggregate together while the hydrophilic carboxylate heads face the water,forming an ionic micelle.
Therefore,the correct option is $A$.

(C) The Tyndall effect is the scattering of light by particles in a colloid or a very fine suspension.
It is observed when the diameter of the dispersed particles is comparable to (similar to) the wavelength of the light used.

(C) $1$. Colloidal solution is a mixture in which tiny particles are suspended in a liquid substance. The suspended particles are known as the dispersed phase and the liquid substance is known as the dispersion medium.
$2$. Colloidal sols are classified as Lyophobic (liquid-hating) and Lyophilic (liquid-loving). Lyophilic sols are inherently more stable due to the high affinity between the dispersed phase and the dispersion medium.
$3$. Egg white contains albumin,which acts as a protective colloid and forms a lyophilic sol when mixed with water. This provides stability to the colloidal system.
$4$. Therefore,egg white ensures the stability of the red ink sample.
$5$. $HCHO$,eosin dye,and water do not possess the property of stabilizing the colloid in this mixture.
Thus,option $(C)$ is correct.

(C) $i$. Foam is a colloidal system where gas is dispersed in a liquid,e.g.,Froth $(i-e)$.
$ii$. Gel is a colloidal system where liquid is dispersed in a solid,e.g.,Jellies $(ii-c)$.
$iii$. Aerosol is a colloidal system where solid or liquid is dispersed in a gas,e.g.,Smoke $(iii-a)$.
$iv$. Emulsion is a colloidal system where liquid is dispersed in a liquid,e.g.,Milk $(iv-f)$.
Therefore,the correct matching is $i-e, ii-c, iii-a, iv-f$.

(C) Surfactants are molecules that contain both a hydrophilic (polar) head and a hydrophobic (non-polar) tail.
In an aqueous solution,at low concentrations,surfactant molecules exist as individual monomers.
As the concentration increases to the Critical Micellar Concentration $(CMC)$,the surfactant molecules begin to aggregate to form spherical structures called micelles.
In a micelle,the hydrophobic tails are directed towards the center (away from water),and the hydrophilic heads are directed towards the outside (in contact with water).
Looking at the provided options,image $(C)$ correctly depicts the formation of a micelle where the non-polar tails are clustered together in the center and the polar heads are facing the aqueous medium.

(C) The Kraft temperature $(T_{k})$ is defined as the minimum temperature above which the formation of micelles takes place in an aqueous solution of surfactants or detergents.

(D) The Zeta potential is the potential difference between the fixed layer and the diffused layer of ions surrounding a colloidal particle.
Greater the magnitude of the Zeta potential,the more stable the colloidal system will be,as it indicates stronger electrostatic repulsion between particles.

(D) The charge on colloidal particles is determined by the nature of the dispersed phase and the dispersion medium. Based on standard chemical classifications:
$1$. Hydrated $Al_{2}O_{3}$ is a positively charged sol.
$2$. $TiO_{2}$ is a positively charged sol.
$3$. Haemoglobin is a positively charged sol.
$4$. Starch is a negatively charged sol.
Therefore,the correct option is $D$.

(D) When $KI$ is added in excess to $AgNO_{3}$,the $AgI$ particles preferentially adsorb $I^{-}$ ions from the dispersion medium to form a negatively charged colloidal sol,represented as $AgI/I^{-}$.
This primary layer of $I^{-}$ ions attracts counter ions $(K^{+})$ from the medium to form the Helmholtz double layer,which is represented as $AgI/I^{-}:K^{+}$.

(A) Lyophilic sols are more stable than lyophobic sols because of the extensive solvation of the dispersed phase particles.
Therefore,the statement $(A)$ is incorrect because it claims that lyophobic sols are more stable.

(D) Micelles are formed only above a particular concentration called Critical Micelle Concentration $(CMC)$ and above a particular temperature called Kraft temperature $(T_k)$.
Therefore,the statement that the formation of micelles takes place below $CMC$ is incorrect.

(A) colloidal system where a gas is dispersed in a solid medium is known as a $solid \ sol$. Examples include pumice stone and rubber foam.

(B) Colloidal solutions exhibit colligative properties due to the presence of particles,although the values are small compared to true solutions.
An ordinary filter paper has large pores that allow colloidal particles to pass through easily; therefore,it cannot stop the flow of colloidal particles.
According to the Hardy-Schulze rule,the flocculating power of an ion increases with the increase in the magnitude of its charge. Thus,$Al^{3+}$ has a much higher flocculating power than $Na^{+}$.
Colloidal particles exhibit Brownian motion due to the unbalanced bombardment of the particles by the molecules of the dispersion medium.
Therefore,statement $B$ is incorrect.

(B) According to the Hardy-Schulze rule,the coagulating power of an ion is directly proportional to the magnitude of its charge.
For a negative sol,the coagulating species must be a cation.
Comparing the given cations: $Na^{+}$ (charge $+1$) and $Ba^{2+}$ (charge $+2$).
Since $Ba^{2+}$ has a higher charge than $Na^{+}$,it will have a higher flocculating power.
Therefore,$Ba^{2+}$ is the correct species.

(D) $CdS$ sol is a negatively charged sol.
$TiO_2$ sol is a positively charged sol.
Therefore,the charges are negative and positive,respectively.

(D) Blood is a negatively charged colloidal sol.
According to the Hardy-Schulze rule,the coagulating power of an electrolyte depends on the valency of the active ion (ion with charge opposite to that of the sol).
For a negatively charged sol,a positively charged ion is required for coagulation.
The coagulating power increases with the increase in the magnitude of the charge on the cation.
Comparing the cations: $Na^+$,$Fe^{2+}$,$Mg^{2+}$,and $Fe^{3+}$.
The $Fe^{3+}$ ion has the highest charge $(+3)$,therefore it has the maximum coagulating power for the negatively charged blood sol.
Thus,$FeCl_3$ is the most suitable salt for the clotting of blood.

(A) The viscosity of hydrophilic sols is generally higher than that of the dispersion medium $(H_2O)$.
Hydrophilic sols are more stable due to strong interaction between the dispersed phase and the dispersion medium,making them difficult to coagulate.
Hydrophilic sols are reversible in nature,meaning they can be reformed by simply mixing the dispersed phase with the dispersion medium after coagulation.
They do not require electrolytes for stability; in fact,the addition of electrolytes can lead to coagulation.
Therefore,the statement that their viscosity is of the order of that of $H_2O$ is false.

(A) When $FeCl_3$ is added to excess of hot water,it undergoes hydrolysis to form hydrated ferric oxide,$Fe_2O_3 \cdot xH_2O$.
During this process,the colloidal particles preferentially adsorb $Fe^{3+}$ ions from the solution,resulting in the formation of a positively charged sol.
The representation is $Fe_2O_3 \cdot xH_2O / Fe^{3+}$.
Therefore,the nature of the charge is positive.

(C) When $AgNO_{3}$ solution is added to $KI$ solution,$AgI$ is formed as a precipitate.
$AgNO_{3(aq)} + KI_{(aq)} \rightarrow AgI_{(s)} + KNO_{3(aq)}$
The precipitated $AgI$ particles preferentially adsorb $I^{-}$ ions from the excess $KI$ present in the dispersion medium,resulting in a negatively charged colloidal sol $(AgI/I^{-})$.
Conversely,when $KI$ is added to $AgNO_{3}$ solution,$AgI$ particles adsorb $Ag^{+}$ ions,forming a positively charged colloidal sol $(AgI/Ag^{+})$.
$FeCl_{3}$ in hot water forms a positively charged $Fe_{2}O_{3} \cdot xH_{2}O$ sol,and $Al_{2}O_{3} \cdot xH_{2}O$ is also typically positively charged.

(C) The Tyndall effect is the scattering of light by particles in a colloid or a very fine suspension.
It is more effectively shown by lyophobic colloids because the particles in lyophobic colloids are relatively larger and have a greater refractive index difference compared to the dispersion medium,leading to more significant scattering of light.

(D) Lyophilic sols are more stable than lyophobic sols because the colloidal particles in lyophilic sols are extensively solvated by the dispersion medium.
This solvation creates a protective layer around the particles,which prevents them from aggregating and precipitating,thereby increasing their stability.

(B) The preparation of colloids by chemical methods involves various reactions:
$1$. Hydrolysis: $FeCl_{3} + 3 H_{2}O \rightarrow Fe(OH)_{3} (sol) + 3 HCl$. This corresponds to $(a)-(iv)$.
$2$. Reduction: $2 AuCl_{3} + 3 HCHO + 3 H_{2}O \rightarrow 2 Au (sol) + 3 HCOOH + 6 HCl$. This corresponds to $(b)-(i)$.
$3$. Oxidation: $SO_{2} + 2 H_{2}S \rightarrow 3 S (sol) + 2 H_{2}O$. This corresponds to $(c)-(iii)$.
$4$. Double Decomposition: $As_{2}O_{3} + 3 H_{2}S \rightarrow As_{2}S_{3} (sol) + 3 H_{2}O$. This corresponds to $(d)-(ii)$.
Thus,the correct matching is $(a)-(iv), (b)-(i), (c)-(iii), (d)-(ii)$.

(C) The Tyndall effect is the scattering of light by particles in a colloid or a very fine suspension.
Among the given options,$NaCl$,glucose,and urea form true solutions,which do not exhibit the Tyndall effect.
Starch forms a colloidal solution,which scatters light and therefore exhibits the Tyndall effect.

(A) The phenomenon of scattering of light by colloidal particles,which makes the path of the beam visible,is called the Tyndall effect.
$1$. The diameter of the dispersed phase particles must be comparable to the wavelength of light used to effectively scatter the light.
$2$. The refractive indices of the dispersed phase and the dispersion medium must differ significantly. If the refractive indices are similar,the scattering is negligible,and the Tyndall effect is not observed.
Therefore,conditions $A$ and $E$ are the necessary requirements for observing the Tyndall effect.

(B) The concentration is given as $0.0018\%(w/v)$,which means $0.0018 \ g$ of $Cl^{-}$ is present in $100 \ mL$ of the solution.
Coagulation value is defined as the minimum concentration of an electrolyte in millimoles per litre $(mmol/L)$ required to cause coagulation of a colloidal sol.
First,calculate the number of moles of $Cl^{-}$:
$Moles = \frac{\text{mass}}{\text{molar mass}} = \frac{0.0018 \ g}{35.5 \ g/mol} \approx 5.07 \times 10^{-5} \ mol$.
Convert moles to millimoles:
$Millimoles = 5.07 \times 10^{-5} \times 1000 = 0.0507 \ mmol$.
Since this amount is present in $100 \ mL$ $(0.1 \ L)$,the concentration in $mmol/L$ is:
$Concentration = \frac{0.0507 \ mmol}{0.1 \ L} = 0.507 \ mmol/L$.
The nearest integer value is $1$.

(B) When $AgNO_{3}$ solution is added to an excess of $KI$ solution,the $AgI$ precipitate adsorbs $I^{-}$ ions from the dispersion medium to form a negatively charged sol.
The reaction is: $AgNO_{3} (aq) + KI (excess) \longrightarrow AgI (sol) / I^{-} + KNO_{3} (aq)$.