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

(D) Water disinfection involves the removal,deactivation,or killing of pathogenic microorganisms. This process prevents their growth and reproduction.
Potassium permanganate $(KMnO_4)$ acts as an oxidizing agent and is used as a mild disinfectant in water treatment to eliminate harmful bacteria.

(B) Metal oxides or some salts are fused with glass to impart colour to glass.

(A) Colligative properties depend on the number of particles in the solution.
Colloidal particles exist as aggregates of many molecules.
For a given mass of substance,the number of colloidal particles present in a colloidal dispersion is much less than the number of particles (ions or molecules) present in a true solution.
Therefore,the magnitude of colligative properties in colloidal dispersions is much lower than that in true solutions.

(D) In the process of dialysis,the rate of diffusion of particles through a semi-permeable membrane depends on the size of the particles.
As the molecular weight of the compound increases,the size of the particles increases,which makes it harder for them to pass through the membrane.
Therefore,the sensitivity or efficiency of the dialysis process decreases as the molecular weight increases.

(D) colloidal system where a liquid is dispersed in a solid is known as a $Gel$.
Examples include cheese,butter,and jellies.
$A$. Aerosol: Liquid or solid in gas.
$B$. Sol: Solid in liquid.
$C$. Foam: Gas in liquid.
$D$. Gel: Liquid in solid.

(B) Gold number is defined as the minimum amount of a lyophilic colloid in $mg$ that must be added to $10 \, mL$ of a standard gold sol to prevent its coagulation when $1 \, mL$ of a $10 \, \% \, NaCl$ solution is added to it.
It is a measure of the protective power of a lyophilic colloid.

(D) Lyophobic sols are solvent-hating and are inherently unstable. They are stabilized only by the presence of an electric charge on the particles. Because they are unstable,they can be easily coagulated by the addition of small amounts of electrolytes. Once coagulated,they cannot be easily reformed into a colloidal state by simply adding the dispersion medium,making them irreversible in nature. Therefore,the statement that they are reversible is incorrect.

(A) Lyophilic sols have a strong affinity for the dispersion medium and are easily solvated,making them stable.
In contrast,lyophobic sols have little affinity for the dispersion medium and are not easily solvated.
Lyophobic sols are less stable,carry a charge,and their coagulation is irreversible in nature.
Therefore,the statement that a lyophobic sol can be easily solvated is false.

(A) According to the Hardy-Schulze rule,the coagulating power of an ion is directly proportional to its valency for the coagulation of a sol.
Since $As_2S_3$ sol is negatively charged,it is coagulated by the addition of positive ions (cations).
The coagulating power of cations follows the order: $Al^{3+} > Ca^{2+} > Na^+$.
Therefore,$AlCl_3$ (which provides $Al^{3+}$ ions) has the highest capacity to precipitate $As_2S_3$ sol.

(C) Starch is a macromolecular substance that has a high affinity for the dispersion medium (water).
When starch is dispersed in hot water,it forms a $Lyophilic$ $sol$.
These sols are stable and reversible in nature.

(D) Ferric hydroxide 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).
The higher the valency of the flocculating ion,the greater is its coagulating power.
The anions provided are $Cl^-$,$NO_3^-$,$SO_4^{2-}$,and $[Fe(CN)_6]^{3-}$.
Since the valency of $[Fe(CN)_6]^{3-}$ is the highest $(3)$,it is the most effective in coagulating the positively charged ferric hydroxide sol.

(D) The sky appears blue due to the scattering of sunlight by the dust particles and air molecules present in the atmosphere,a phenomenon known as the Tyndall effect.

(B) gel is a colloidal system where a liquid is dispersed in a solid medium.
Cheese is a classic example of a gel where liquid fat/water is dispersed in a solid protein matrix.

(C) Colloidal sol particles in a dispersion medium are continuously bombarded by the molecules of the dispersion medium from all sides.
As a result,the particles exhibit a continuous zig-zag motion,which is known as $Brownian$ motion.

(C) Ferric hydroxide 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.
The anions provided are: $[Fe(CN)_6]^{4-}$,$CrO_4^{2-}$,$Br^-$,and $SO_4^{2-}$.
The valencies are: $4$,$2$,$1$,and $2$ respectively.
Since $Br^-$ has the lowest valency $(1)$,it is the least effective in causing flocculation.

(C) . $\text{Liquid (dispersed phase)} + \text{Solid (dispersion medium)} = \text{Gel (colloid)}$.
Examples include butter,cheese,and jelly.

(C) The zig-zag motion of colloidal particles is known as Brownian motion. This phenomenon was first observed by the botanist $Robert \ Brown$ in $1827$ while observing pollen grains suspended in water.

(D) The gold number is defined as the minimum amount of protective colloid in $mg$ that must be added to $10 \, mL$ of a standard gold sol to prevent its coagulation when $1 \, mL$ of $10\% \, NaCl$ solution is added to it.
Given that the amount of starch required is $0.25 \, g$.
Converting this to milligrams: $0.25 \, g = 0.25 \times 1000 \, mg = 250 \, mg$.
Since this amount of starch prevents the coagulation of $10 \, mL$ of gold sol,the gold number of starch is $250$.

(B) The Tyndall effect is the phenomenon of light scattering by particles in a colloidal dispersion.
True solutions do not exhibit the Tyndall effect because their particles are too small to scatter light effectively.
Therefore,the Tyndall effect is observed in a colloidal solution.

(C) According to the $Hardy-Schulze$ rule,the ions carrying a charge opposite to that of the colloidal particles are responsible for coagulation.
Greater the valency of the oppositely charged ion,the higher is its coagulating power.
Since ferric hydroxide sol is positively charged,it requires negatively charged ions for coagulation.
The valencies of the given ions are $PO_4^{3-} (3)$,$SO_4^{2-} (2)$,and $NO_3^- (1)$.
Therefore,the order of coagulating power is $PO_4^{3-} > SO_4^{2-} > NO_3^-$.

(D) The purification of a colloidal solution involves the removal of dissolved impurities (crystalloids) from the sol.
This is achieved by the process of $Dialysis$.
In this process,the impure sol is placed in a bag made of a suitable membrane,such as parchment paper or cellophane,which allows only the small impurity particles to diffuse out into the surrounding water,while the larger colloidal particles are retained inside.

(B) $Gold$ number is a measure of the protective power of a lyophilic colloid. It is defined as the minimum mass of a protective colloid in $mg$ that must be added to $10 \ mL$ of a standard red gold sol so that no coagulation occurs when $1 \ mL$ of $10\% \ NaCl$ solution is added to it. Thus,it is associated with only lyophilic colloids.

(A) According to the Hardy-Schulze rule,the coagulating power of an electrolyte depends on the valency of the active ion (the ion carrying a charge opposite to that of the colloidal particles).
For a negatively charged clay sol,the coagulating power depends on the cation.
The coagulating power increases with the increase in the valency of the cation $(Al^{3+} > Ca^{2+} > Na^+)$.
Therefore,the electrolyte with the highest valency of the cation will require the minimum amount for precipitation.
$AlCl_3$ provides $Al^{3+}$ ions,which have the highest valency among the given options.

(B) Crystalloids are substances that can be easily crystallized from their aqueous solutions.
Colloids contain much larger particles than crystalloids,typically in the range of $1-200 \ nm$.
Crystalloids contain much smaller particles than colloids,typically less than $1 \ nm$.
Therefore,the fundamental difference between them is the particle size.

(B) The process of separating the particles of colloids from those of crystalloids by means of diffusion through a suitable membrane is called $Dialysis$.
Colloidal particles cannot pass through a semipermeable membrane (like parchment paper or cellophane),whereas crystalloid particles can pass through it easily.
In this process,the impure sol is placed in a bag made of a semipermeable membrane and suspended in a vessel containing distilled water.
The crystalloid impurities diffuse out into the water,leaving behind pure colloidal particles.

(B) Lyophilic colloids possess a solvent-loving nature.
Due to this,a protective layer of the dispersion medium is formed around the sol particles,which prevents them from aggregating and provides stability.

(A) Milk is an emulsion,which is a type of colloid where a liquid is dispersed in another liquid.
Specifically,in milk,fat globules (liquid) are dispersed in water (liquid).

(A) The gold number is a measure of the protective power of a lyophilic colloid.
Lower gold number indicates higher protective power.
Gelatin has the lowest gold number,typically in the range of $0.005 - 0.01$,making it the most effective protective colloid among the given options.

(A) The movement of charged colloidal particles under the influence of an applied electric field is known as electrophoresis. When an electric potential is applied across two platinum electrodes dipping in a colloidal solution,the colloidal particles move towards one or the other electrode depending on the charge they carry.

(C) $Fe(OH)_3$ gives a positively charged sol because it adsorbs $Fe^{3+}$ ions from the $FeCl_3$ solution during its preparation.

(D) The phenomenon of light scattering by colloidal particles is known as the $Tyndall$ effect. Colloidal particles are too small to be seen under an ordinary microscope,but they can be detected using an ultra-microscope. The ultra-microscope does not make the actual colloidal particles visible,but it detects the light scattered by them.

(A) The flocculation value is defined as the minimum concentration of an electrolyte in $mmol \ L^{-1}$ required to cause the coagulation or flocculation of a colloidal solution. Therefore,it is expressed in terms of $millimole \ per \ litre$.

(A) Suspensions are heterogeneous mixtures in which the particle size is larger than $1000 \ nm$ $(10^{-6} \ m)$.
These particles are large enough to be seen with the naked eye.

(B) Gelatin acts as a protective colloid. In ice cream,it prevents the formation of large ice crystals by stabilizing the emulsion,thereby ensuring a smooth texture.

(C) An emulsion is a type of colloid where both the dispersed phase and the dispersion medium are liquids.
In this system,one liquid is dispersed in another immiscible liquid.

(C) The stability of lyophilic sols is a result of two factors: the presence of a charge and the solvation of colloidal particles.
On the other hand,the stability of lyophobic sols is only due to the presence of a charge.
Thus,the lyophilic sol is more stable than the lyophobic sol due to the extensive solvation of the particles by the dispersion medium.

(B) Milk is a natural emulsion where fat globules are dispersed in water.
It is stabilized by proteins,specifically casein,which acts as an emulsifying agent by forming a protective layer around the fat globules to prevent them from coalescing.

(B) According to the $Hardy-Schulze$ rule,the coagulating power of an electrolyte depends on the valency of the active ion (the ion with a charge opposite to that of the colloidal particles).
Greater the valency of the flocculating ion,the greater is its coagulating power.
In the given options,$ZnCl_2$ dissociates to give $Zn^{2+}$ ions,while $KCl$ and $NaCl$ dissociate to give $K^+$ and $Na^+$ ions respectively.
Since the charge on $Zn^{2+}$ $(+2)$ is greater than the charge on $K^+$ $(+1)$ and $Na^+$ $(+1)$,$ZnCl_2$ has the maximum coagulating power.
$CCl_4$ is a covalent compound and does not dissociate into ions.

(C) Air is not a colloidal solution because it is a homogeneous mixture.

(A) The detergent action of soap is primarily due to its ability to form micelles and emulsify oil and grease particles. The hydrophobic tail of the soap molecule attaches to the grease,while the hydrophilic head remains in the water,leading to the emulsification of the dirt into the water.

(D) colloid is a heterogeneous system in which one substance is dispersed (dispersed phase) as very fine particles in another substance called the dispersion medium.
When the dispersion medium is water,the colloidal system is specifically known as an $Aquasol$ or $Hydrosol$.

(B) The process of converting a freshly prepared precipitate into a colloidal sol by adding a small amount of an electrolyte is known as $Peptization$. The electrolyte added is called a $Peptizing \ agent$.

(D) According to the Hardy-Schulze rule,the coagulating power of an ion is directly proportional to its valency (charge).
$As_2S_3$ is a negatively charged sol.
Therefore,it requires a positively charged ion for coagulation.
Among the given options,$Al^{3+}$ has the highest positive charge $(+3)$.
Thus,$Al^{3+}$ will have the highest coagulating power.

(D) Hydrophobic sols are those in which the dispersed phase has little or no affinity for the dispersion medium (water).
Starch,gum,and proteins are examples of hydrophilic sols because they have a strong affinity for water.
$As_2S_3$ (Arsenic sulphide) sol is a classic example of a hydrophobic sol,as it does not have an affinity for water and is easily coagulated by the addition of small amounts of electrolytes.

(D) In the purification of colloids,the separation of colloidal particles from crystalloids is achieved through the process of ultra-filtration.

(C) Brownian movement is the random motion of colloidal particles suspended in a fluid.
Dialysis is a process used for the purification of colloidal solutions by removing dissolved ions or small molecules.
Ultrafiltration is a technique used to separate colloidal particles from the dispersion medium using special filters.
Wavelength is a property of waves and is not associated with the physical or chemical properties of colloids.

(B) The colloidal system formed when the dispersed phase is liquid and the dispersion medium is gas is known as an aerosol (specifically,clouds or fog).
$B$ is the correct option.
$\text{Dispersed phase (liquid)} + \text{Dispersion medium (gas)} = \text{Aerosol (Clouds/Fog)}$

(B) Tyndall phenomenon is exhibited by starch solution because starch solution is a colloidal solution.
Colloidal particles are large enough to scatter light,which is the basis of the Tyndall effect.
$NaCl$,urea,and $FeCl_3$ (in true solution form) form true solutions,which do not exhibit the Tyndall effect.

(D) Gelatin is a protein that forms a colloidal solution in water.
It is classified as a $hydrophilic$ colloid because it has a strong affinity for the dispersion medium (water).
It is also known as a $solvent-loving$ sol.
Furthermore,gelatin exhibits the property of reversibility,where the sol can be converted into a gel upon cooling and back into a sol upon heating.
Therefore,all the given descriptions are correct.

(D) The zig-zag random movement of microscopic particles in a fluid,as a result of continuous collision from molecules of the surrounding medium is called $Brownian$ movement.