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

(B) Colloidal particles are defined as particles having a diameter in the range of $1 \, nm$ to $1000 \, nm$ ($10^{-9} \, m$ to $10^{-6} \, m$).
This range is intermediate between true solutions (particle size $< 1 \, nm$) and suspensions (particle size $> 1000 \, nm$).

(D) Arsenic sulphide $As_2S_3$ is a negatively charged sol.
It will be coagulated by ions carrying a positive charge.
In the given options,the cations are $Mg^{2+}$,$K^+$,$K^+$,and $Al^{3+}$.
According to the Hardy-Schulze rule,the greater the valence of the coagulating ion,the greater is its coagulating power.
Since $Al^{3+}$ has the highest positive charge $(+3)$,it has the maximum coagulating power.
Therefore,the minimum concentration of $Al(NO_3)_3$ is required to coagulate the $As_2S_3$ sol.

(B) When a beam of light is passed through a colloidal solution,the colloidal particles scatter the light in all directions. This phenomenon is known as the $Tyndall \ effect$,which makes the path of the light beam visible.

(A) The process of converting a precipitate into a colloidal sol by shaking it with a dispersion medium in the presence of a small amount of electrolyte is called $Peptization$.
Therefore,the correct option is $A$.

(C) Dialysis is a process used to purify colloidal solutions.
It involves the separation of colloidal particles from dissolved ions or small molecules by allowing the latter to pass through a semipermeable membrane while the larger colloidal particles are retained.

(A) The colour of a colloidal solution depends upon the size of colloidal particles present in it.
Larger particles absorb light of longer wavelengths and transmit light of shorter wavelengths.
For example,a silver sol having particles of size $150 \, nm$ appears violet,whereas that having particles of size $60 \, nm$ appears orange-yellow.

(A) Scattering of light,also known as the Tyndall effect,is a characteristic property of colloids.

(A) The particle size of a true solution is less than $1 \, nm$ in diameter,which cannot be seen by the naked eye.
The particle size of a colloid ranges between $1 \, nm$ and $1000 \, nm$,making them larger than particles of true solutions but smaller than those of suspensions.
The particle size of a suspension is greater than $1000 \, nm$,which can be seen by the naked eye.
Therefore,the order of particle size is: $\text{Suspension} > \text{Colloidal} > \text{True solution}$.

(C) In lyophilic sols,the dispersed phase particles have a strong affinity for the dispersion medium. This attraction is primarily due to the formation of $Hydrogen \ bonds$ between the particles of the dispersed phase and the molecules of the dispersion medium.

(C) Gelatin acts as a protective colloid for the gold sol.
When a lyophilic colloid like gelatin is added to a lyophobic colloid like gold sol,it forms a protective layer around the gold particles.
This prevents the coagulation of the gold sol by electrolytes,a process known as the protection of gold sol.

(D) An emulsifier is a substance that stabilizes an emulsion by increasing its kinetic stability.
Soaps,synthetic detergents,and lyophilic colloids (like proteins or gums) can all act as emulsifying agents.
Therefore,all of the given options are correct.

(A) colloid consists of a dispersed phase and a dispersion medium.
Shaving cream is a type of colloid known as foam.
In foam,a gas is dispersed in a liquid.
Therefore,the dispersed phase is gas and the dispersion medium is liquid.

(D) The molar mass of $NaCl$ is $58.5 \ g/mol$.
Number of moles $= \frac{\text{mass}}{\text{molar mass}} = \frac{0.585 \ g}{58.5 \ g/mol} = 0.01 \ mol = 10 \ mmol$.
The flocculation value is defined as the minimum concentration of an electrolyte in $mmol/L$ required to cause precipitation of a sol.
Flocculation value $= \frac{\text{millimoles of electrolyte}}{\text{Volume of sol in litres}} = \frac{10 \ mmol}{10 \ L} = 1 \ mmol/L$.

(A) micellar system is formed by the aggregation of surfactant molecules in a solvent above the Critical Micelle Concentration $(CMC)$.
Soap molecules consist of a hydrophilic head (carboxylate group) and a hydrophobic hydrocarbon tail.
In water,these molecules aggregate to form micelles where the hydrophobic tails point inward and the hydrophilic heads point outward toward the water.
Therefore,$Soap + water$ is a classic example of a micellar system.

(B) $\Delta$ at the rivers are formed due to the coagulation of colloidal particles present in river water by the electrolytes present in sea water.

(B) The Tyndall effect depends on the difference between the refractive index of the dispersed phase and the dispersion medium.
In hydrophobic sols,the particles are larger and the interaction between the dispersed phase and the dispersion medium is weak,leading to a significant difference in refractive index.
Therefore,the Tyndall effect is more pronounced in hydrophobic sols compared to hydrophilic sols,which are more stable and have particles that are highly solvated.

(A) The correct option is $(A)$.
An emulsifier is a substance that is added to an emulsion to stabilize it by preventing the dispersed droplets from coalescing. Therefore,it increases the stability of the emulsion.

(A) The process of converting a freshly prepared precipitate into a colloidal sol by adding a suitable electrolyte is known as peptization.
In this case,the coagulated egg white is converted back into a colloidal state using pepsin and $HCl$.

(D) Sugar is a non-electrolyte and a non-ionic substance. When added to a colloidal solution,it does not provide ions to neutralize the charge on colloidal particles,nor does it affect the stability of the colloid significantly. Therefore,it does not cause coagulation,ionization,or peptization. Thus,the correct option is $(D)$.

(B) The method of preparation of colloidal solutions of metals such as platinum,gold,or silver is known as $Bredig's$ arc method.
It involves both dispersion and condensation processes.
It cannot be used to prepare colloidal solutions of metals like copper or sodium.

(B) colloidal system in which both the dispersed phase and the dispersion medium are liquids is called an emulsion. Therefore,liquid-liquid sols are known as emulsions.

(C) The Tyndall effect is the scattering of light by colloidal particles.
It depends on two main factors:
$1$. The difference between the refractive indices of the dispersed phase and the dispersion medium.
$2$. The size of the colloidal particles,which must be comparable to the wavelength of the light used.

(B) Lyophilic colloids like Gelatin act as protective colloids because they form a protective layer around lyophobic colloids,preventing their coagulation.
Gelatin has a very low gold number,which indicates that it is a highly effective protective colloid.

(C) heteropolar sol is a colloidal system where the dispersed phase particles possess both polar and non-polar groups,or exhibit amphiphilic character.
Among the given options,$(c)$ Protein sol in water is an example of a heteropolar sol because protein molecules contain both hydrophilic (polar) and hydrophobic (non-polar) amino acid residues.

(D) In Bredig's arc method,an electric arc is struck between metal electrodes immersed in a dispersion medium.
Small amounts of alkali (like $KOH$) are added to the dispersion medium to act as a stabilizing agent.
This helps in stabilizing the resulting colloidal sol by preventing the aggregation of particles.
Therefore,the correct option is $(D)$.

(C) solution of urea is a true solution,not a colloid. Colloids are heterogeneous mixtures where particle sizes range between $1 \ nm$ and $1000 \ nm$. Milk,blood,and ice cream are examples of colloidal systems.

(C) Dialysis is a purification technique used to remove dissolved impurities (crystalloids) from a colloidal solution by means of diffusion through a suitable membrane.

(D) The minimum concentration of an electrolyte required to cause the coagulation or precipitation of a colloidal sol is defined as the flocculation value (or coagulation value).
It is usually expressed in $mmol \ L^{-1}$.

(D) Whipped cream is a type of colloid known as a foam.
In a foam,a gas is dispersed in a liquid.
Therefore,the dispersed phase is $Gas$ and the dispersion medium is $Liquid$.
Thus,the correct option is $D$.

(B) Milk is a type of emulsion where the dispersed phase is liquid fat and the dispersion medium is water. Therefore,it is classified as $O/W$ (oil-in-water) emulsion.

(B) Alum is a coagulating agent,frequently added to water to remove suspended and colloidal impurities.
This is because the colloidal impurities in water are typically negatively charged,and $Alum$ $(K_2SO_4 \cdot Al_2(SO_4)_3 \cdot 24H_2O)$ provides $Al^{3+}$ ions,which neutralize the negative charge and cause coagulation.

(C) The process of converting a freshly prepared precipitate into a colloidal sol by adding a small amount of a suitable electrolyte is known as $Peptization$.
In this case,$FeCl_3$ acts as the peptizing agent for $Fe(OH)_3$ precipitate,forming a reddish-brown colloidal solution.

(C) Alum $(K_2SO_4 \cdot Al_2(SO_4)_3 \cdot 24H_2O)$ provides $Al^{3+}$ ions in water.
These $Al^{3+}$ ions neutralize the negative charge on the colloidal clay particles present in muddy water.
This process leads to the aggregation and settling of these particles,which is known as coagulation.

(D) Lyophilic sols are highly stable because the particles have a strong affinity for the dispersion medium,which results in a solvation layer around them.
They are reversible in nature,meaning they can be reformed after coagulation.
They do not necessarily carry a charge.
Therefore,the statement that they are not very stable is incorrect.

(B) Gelatin in water forms a colloidal system where the liquid is dispersed in a solid or forms a semi-solid structure upon cooling,which is classified as a $Gel$.

(C) The size of colloidal particles generally ranges from $1 \, nm$ to $1000 \, nm$,which is equivalent to $10 \,\mathring{A}$ to $10000 \,\mathring{A}$.
Among the given options,the range $10 \,\mathring{A}$ to $1000 \,\mathring{A}$ is the most appropriate representation for colloidal particles.

(A) Blood is a colloidal system in which the dispersed phase consists of negatively charged particles (like albumin and other proteins).
According to the Hardy-Schulze law,the coagulating power of an ion increases with the increase in the magnitude of the charge on the ion.
$FeCl_3$ dissociates to provide $Fe^{3+}$ ions.
Since $Fe^{3+}$ ions are highly positively charged,they effectively neutralize the negative charge on the blood colloids,leading to coagulation and stopping the bleeding.

(C) At $CMC$ (critical micellization concentration),the surfactant molecules associate to form micelles.
For soap,the $CMC$ value is approximately $10^{-3} \ mol \ L^{-1}$.

(C) Benzene is a non-polar molecule. According to the principle of 'like dissolves like',non-polar substances are better dispersed by other non-polar substances.
$m$-methyl nonylbenzene is a non-polar molecule with a long hydrocarbon chain and a substituted benzene ring,making it highly lipophilic and suitable for dispersing non-polar benzene.
In contrast,options $(A)$,$(B)$,and $(D)$ contain polar functional groups (carboxylate ions or chlorine atoms),which make them amphiphilic or polar,thus less suitable for dispersing pure non-polar benzene compared to the purely non-polar $m$-methyl nonylbenzene.

(B) The phenomenon of scattering of light by particles is known as the $Tyndall$ effect.
This effect is observed in colloidal solutions because the size of colloidal particles is large enough to scatter light in all directions.
In true solutions,the particles are too small to scatter light,and in suspensions,particles are too large and often settle down.

(D) The stability of lyophilic sols is primarily due to two factors: the charge on the colloidal particles and the solvation (hydration) of the particles.
To make a lyophilic sol unstable (i.e.,to cause coagulation),both of these stabilizing factors must be removed.
This is achieved by adding a suitable solvent (like alcohol or acetone) to dehydrate the particles and by adding an electrolyte to neutralize the charge.
Therefore,the addition of both alcohol and an electrolyte makes the lyophilic solution unstable.

(A) The protective action of different lyophilic colloids is expressed in terms of Gold number. It is defined as the minimum mass of a protective colloid in milligrams that prevents the coagulation of $10 \ mL$ of a gold sol when $1 \ mL$ of $10\%$ $NaCl$ solution is added to it.

(B) When the dispersed phase and dispersion medium both are liquid,the colloidal system is called an emulsion,such as milk,vanishing cream,etc.

(D) The stability of colloids is maintained by the charge on the particles. By adding an electrolyte,the charge on the colloidal particles is neutralized. This leads to the coagulation or precipitation of the colloidal particles,effectively destroying the colloid.

(B) Associated colloids are substances that behave as normal strong electrolytes at low concentrations but exhibit colloidal behavior at higher concentrations due to the formation of aggregates called micelles.
Soap solution is a classic example of an associated colloid because soap molecules (like sodium stearate) form micelles in water above the critical micelle concentration $(CMC)$.

(A) The movement of colloidal particles towards the oppositely charged electrodes on passing electricity is known as cataphoresis. This phenomenon is also referred to as electrophoresis.

(A) Tyndall effect is defined as the scattering of light by the colloidal particles present in a colloidal sol.

(A) The colour of colloidal solutions depends on the wavelength of light scattered by the dispersed particles.
This wavelength further depends on the size and nature of the particles.
In the case of gold sol,the size of the colloidal particles varies depending on the method of preparation,which leads to the scattering of different wavelengths of light,resulting in different colours.

(A) The reaction between arsenious oxide $(As_2O_3)$ and hydrogen sulphide $(H_2S)$ is a double decomposition reaction:
$As_2O_3 + 3H_2S \rightarrow As_2S_3 (sol) + 3H_2O$.
This results in the formation of an $As_2S_3$ sol,which is a negatively charged colloid.
The negative charge is due to the preferential adsorption of $S^{2-}$ ions on the surface of the colloidal particles.

(A) The $Tyndall \ effect$ is an easy way of determining whether a mixture is colloidal or not.
When light is directed through a true solution,the light passes cleanly through the solution.
However,when light is passed through a colloidal solution,the substance in the dispersed phase scatters the light in all directions,making the path of the beam visible.