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

(A) Fog is a colloidal system where a liquid (water droplets) is dispersed in a gas (air). Therefore,it is classified as an aerosol of liquid in gas.

(B) The gold number is defined as the minimum amount of protective colloid in milligrams that prevents a color change from red to violet of $10 \, mL$ of gold sol upon the addition of $1 \, mL$ of $10 \, \% \, NaCl$ solution.
Therefore,the electrolyte used in this measurement is $NaCl$.

(A) Blood is a colloidal system that contains crystalloids as impurities.
These impurities can be separated from the colloidal particles of blood through the process of $Dialysis$.

(A) Lyophilic sols are liquid-loving colloids. Their stability is primarily due to two factors:
$1$. The presence of a charge on the colloidal particles.
$2$. The extensive solvation of the particles,where the solvent molecules form a protective layer around the dispersed phase particles,preventing them from aggregating.
Therefore,both charge and solvation contribute to their stability.

(B) The colloidal impurities present in rain water are generally negatively charged. This is why they can be coagulated by adding electrolytes containing positive ions.

(B) Sodium lauryl sulphate $(CH_3(CH_2)_{11}OSO_3^-Na^+)$ dissociates in aqueous solution to give a long chain anion $(CH_3(CH_2)_{11}OSO_3^-)$ and a sodium cation $(Na^+)$.
Since the surface active part of the molecule is the anion,it is classified as an anionic surfactant.

(C) The statement that 'Every solid substance can be made to behave like a lyophilic colloid' is false.
Lyophilic colloids are substances that have a strong affinity for the dispersion medium.
Not all solid substances possess this property; many solids form lyophobic colloids,which have little to no affinity for the dispersion medium.

(C) colloid is a heterogeneous system in which one substance is dispersed as very fine particles in another substance.
Sugar solution,urea solution,and $NaCl$ solution are true solutions because the solute particles are completely dissolved and form a homogeneous mixture.
Silicic acid $(H_4SiO_4)$ forms a colloidal sol in water because the particles are of colloidal dimensions ($1 \ nm$ to $1000 \ nm$).

(C) Alum $(K_2SO_4 \cdot Al_2(SO_4)_3 \cdot 24H_2O)$ dissociates in water to provide $Al^{3+}$ ions.
These $Al^{3+}$ ions neutralize the charge on the negatively charged colloidal mud particles.
This process is known as coagulation or flocculation,which causes the mud particles to settle down,thereby purifying the water.

(D) According to the Hardy-Schulze rule,the coagulation power of an ion is directly proportional to the magnitude of the charge on the ion.
Comparing the charges:
$Na^{+}$ has a charge of $+1$.
$Ba^{+2}$ has a charge of $+2$.
$Al^{+3}$ has a charge of $+3$.
$Sn^{+4}$ has a charge of $+4$.
Since $Sn^{+4}$ has the highest charge,it possesses the maximum coagulation power.

(D) An emulsion is a colloidal system where both the dispersed phase and the dispersion medium are liquids.
$A$,$B$,and $C$ (Butter,Ice cream,and Milk) are examples of emulsions.
$D$ (Cloud) is an aerosol,which is a colloidal system where a liquid is dispersed in a gas.
Therefore,the correct answer is $D$.

(D) Colloidal solutions of metals like gold,silver,and platinum are typically prepared by Bredig's arc method or by the reduction of their salt solutions (e.g.,reduction of $AuCl_3$ with formaldehyde or stannous chloride).
Mechanical dispersion is generally used for substances like sulfur or ink.
Exchange of solvents is used for substances like sulfur or phosphorus,which are soluble in alcohol but insoluble in water.
Therefore,the colloidal solution of gold cannot be prepared by the exchange of solvents.

(A) Proteins are lyophilic colloids that can be coagulated by the addition of heavy metal ions.
$Ag^{+}$ is a heavy metal ion that interacts with the functional groups of proteins,leading to their denaturation and subsequent coagulation.
Alkali metal ions like $Na^{+}$ and alkaline earth metal ions like $Mg^{2+}$ and $Ca^{2+}$ are generally less effective at causing coagulation compared to heavy metal ions.

(B) The scattering of light by colloidal particles is known as the $Tyndall \ effect$. This phenomenon occurs specifically in colloidal solutions because the size of the particles is large enough to scatter light,whereas true solutions do not show this effect.

(B) Gold sol is a lyophobic sol,which is unstable and easily coagulated by electrolytes like $NaCl$.
Gelatin is a lyophilic colloid.
When added to a lyophobic sol,lyophilic colloids form a protective layer around the lyophobic particles,preventing their coagulation by electrolytes.
This phenomenon is known as the protective action of colloids.

(C) At the isoelectric point,the net charge on the colloidal particles becomes zero,meaning they become uncharged. Due to the lack of electrostatic repulsion,the particles aggregate and settle down,leading to the precipitation of the colloidal sol. Therefore,both $B$ and $C$ are technically correct,but $C$ describes the fundamental state at the isoelectric point.

(C) Multimolecular colloids are formed by the aggregation of a large number of atoms or smaller molecules (diameter $< 1 \ nm$).
Gold sol is a classic example of a multimolecular colloid where many gold atoms aggregate to form particles of colloidal size.
Soap in water forms associated colloids (micelles),while proteins and gum are examples of macromolecular colloids.

(A) colloidal system in which gas bubbles are dispersed in a liquid is known as foam.

(A) 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,the addition of $HCl$ or $FeCl_3$ acts as a peptizing agent for the freshly precipitated ferric hydroxide,resulting in a red-coloured colloidal solution.

(A) The surface tension of lyophilic sols is generally lower than that of the pure dispersion medium (in this case,$H_2O$).
This is because the solute particles (colloidal particles) are strongly solvated by the dispersion medium,which reduces the cohesive forces at the surface.

(B) Lyophilic (hydrophilic) colloids act as protective colloids. When a lyophilic sol is added to a lyophobic (hydrophobic) sol,the lyophilic particles form a protective layer around the lyophobic particles,preventing them from coagulation in the presence of electrolytes.

(D) is the correct answer.
Lyophilic sols are solvent-loving colloids formed by substances like starch,gum,and gelatin.
Metal sulphides are examples of lyophobic (solvent-hating) colloids,which are prepared by special methods and are not lyophilic.

(B) Soap molecules consist of a hydrophobic hydrocarbon tail and a hydrophilic polar head. When soap is added to water,it forms micelles. The hydrophobic tails dissolve in the grease,while the hydrophilic heads remain in the water. This process breaks the grease into small droplets,which are then washed away by water. This mechanism is known as $Emulsification$.

(C) 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 an electronegative sol like gold sol,the coagulating power depends on the cation.
The higher the valency of the cation,the greater is its coagulating power,and thus,the minimum amount of electrolyte is required.
The valencies of the cations in the given options are: $Na^+$ $(+1)$,$Ca^{2+}$ $(+2)$,and $Al^{3+}$ $(+3)$.
Since $Al^{3+}$ has the highest valency,$AlCl_3$ will have the maximum coagulating power,requiring the minimum amount for coagulation.

(D) Potash alum $(K_2SO_4 \cdot Al_2(SO_4)_3 \cdot 24H_2O)$ is a salt that provides $Al^{3+}$ ions.
Blood is a colloidal solution of negatively charged particles.
When potash alum is applied to a cut,the $Al^{3+}$ ions neutralize the charge on the blood colloids,causing them to coagulate.
Thus,alum acts as a coagulating agent to stop the bleeding.

(A) The protective power of a lyophilic colloid is inversely proportional to its gold number.
$\text{Protective power} \propto \frac{1}{\text{Gold number}}$
Given gold numbers are:
$A = 0.005$
$B = 0.05$
$C = 0.5$
$D = 5$
Since $A$ has the lowest gold number $(0.005)$,it possesses the highest protective power.

(B) . Bredig's arc method is suitable for the preparation of colloidal solutions of metals like gold,silver,and platinum.
An electric arc is struck between the metal electrodes under the surface of water containing a stabilizing agent,such as a trace of $KOH$.
However,$Fe$ does not form a stable colloidal sol using this method because it does not react with the stabilizing agent in the same way as noble metals,and it is prone to oxidation. Therefore,$Fe$ is not typically prepared by Bredig's arc method.

(D) The gold number is a measure of the protective power of a lyophilic colloid.
It is defined as the minimum amount of the protective colloid (in $mg$) that must be added to $10 \ mL$ of a standard red gold sol to prevent its coagulation when $1 \ mL$ of a $10\%$ $NaCl$ solution is added.
Lower gold number indicates higher protective power.
Among the given options,Gelatin has a very low gold number $(0.005-0.01)$,while Potato starch has a significantly higher gold number $(20-25)$.
Therefore,the gold number is maximum for Potato starch.

(A) The protective power of a colloid is inversely proportional to its Gold number.
$Protective \ power \propto \frac{1}{\text{Gold number}}$
Since gelatin has the lowest Gold number $(0.005)$,it possesses the highest protective power.
Therefore,gelatin is the best protective colloid.

(A) colloid of liquid in liquid is called an emulsion. Cod liver oil is an example of an emulsion where oil droplets are dispersed in water.

(A) paste is defined as a system where a solid is dispersed in a liquid,typically characterized by a high concentration of the solid phase. Therefore,it is considered a suspension of a solid in a liquid. The correct option is $A$.

(C) The process of converting a freshly prepared precipitate into a colloidal sol by adding a suitable electrolyte is known as $Peptization$.
Therefore,the correct option is $(C)$.

(A) An aerosol is a colloidal system where the dispersed phase is either a solid or a liquid,and the dispersion medium is a gas.
Therefore,the correct option is $(A)$.

(D) Lyophilic sols are self-stabilizing because these sols are reversible and are highly hydrated in the solution.

(D) The size of a true solution particle is typically in the range of $10^{-10} \ m$ to $10^{-9} \ m$ (diameter),while a colloidal particle is in the range of $10^{-9} \ m$ to $10^{-6} \ m$ (diameter).
Assuming an average diameter for a true solution particle $d_S \approx 10^{-10} \ m$ and for a colloidal particle $d_C \approx 10^{-9} \ m$.
The volume $V$ of a spherical particle is given by $V = \frac{4}{3} \pi r^3 = \frac{1}{6} \pi d^3$.
Therefore,the ratio of volumes is $\frac{V_C}{V_S} = \frac{d_C^3}{d_S^3} = (\frac{10^{-9}}{10^{-10}})^3 = (10^1)^3 = 10^3$.
Thus,the ratio is approximately $10^3$.

(C) The iron $(III)$ hydroxide sol is positively charged,while the gold sol is negatively charged.
$(A)$ According to the Hardy-Schulze rule,the coagulating power of an ion is directly proportional to its charge. For the negatively charged gold sol,the coagulating power of cations $(Mg^{2+} > Na^+)$ is significant. For the positively charged iron $(III)$ hydroxide sol,the coagulating power of anions $(SO_4^{2-} > Cl^-)$ is significant. Magnesium chloride contains $Mg^{2+}$ ions,which are effective for the gold sol,but not for the iron $(III)$ hydroxide sol. Thus,the statement is correct.
$(B)$ Sodium sulphate $(Na_2SO_4)$ provides $Na^+$ ions (which coagulate the gold sol) and $SO_4^{2-}$ ions (which coagulate the iron $(III)$ hydroxide sol). Thus,the statement is correct.
$(C)$ When two oppositely charged sols are mixed,they neutralize each other's charges,leading to mutual coagulation. Therefore,saying that mixing has no effect is incorrect.
$(D)$ Electrophoresis involves the movement of charged colloidal particles under an electric field,which leads to their discharge and subsequent coagulation at the electrodes. Thus,the statement is correct.

(B) Micelles are formed by surfactants or detergents in an aqueous solution above a specific concentration known as the Critical Micelle Concentration $(CMC)$.
Among the given options,$Dodecyl trimethyl ammonium chloride$ is a cationic surfactant (detergent).
$Urea$,$Pyridinium chloride$,and $Glucose$ do not form micelles in aqueous solutions.
Therefore,the correct answer is $Dodecyl trimethyl ammonium chloride$.

(A) Alum $(K_2SO_4 \cdot Al_2(SO_4)_3 \cdot 24H_2O)$ contains $Al^{3+}$ ions.
When added to water,it undergoes hydrolysis to form $Al(OH)_3$ precipitate.
This precipitate is gelatinous and carries a positive charge,which neutralizes the negatively charged colloidal impurities present in water.
This process is known as coagulation,which causes the impurities to settle down,making the water clear and fit for drinking.

(A) For the stabilisation of an emulsion,a third component called an emulsifying agent is usually added. The emulsifier forms an interfacial film between the suspended particles and the dispersion medium.

(B) Alum is added to muddy water to coagulate the suspended clay particles,which are negatively charged,by the action of $Al^{3+}$ ions. This process helps in clearing the water.

(B) Fog is an example of an aerosol where the dispersed phase is a liquid and the dispersion medium is a gas.

(C) Lyophilic sols are more stable than lyophobic sols because the particles in lyophilic sols have a strong affinity for the dispersion medium,leading to extensive solvation. This solvation layer acts as a protective barrier,preventing the particles from aggregating and precipitating out of the solution.

(D) The substance,whose molecules associate in a given solvent to form colloidal particles,is known as an associated colloid.
Soap and detergent molecules are generally smaller than colloidal particles.
These molecules associate in concentrated solutions to form particles of colloidal size.
These associations of soap and detergent are known as micelles.

(A) Lyophilic means liquid-loving. The particles of the dispersed phase have a strong affinity for the dispersion medium,which leads to extensive solvation or hydration. This hydration layer acts as a protective barrier,contributing to the extra stability of lyophilic colloids.

(D) The correct answer is $(d)$.
Traces of electrolytes are essential for stabilizing the sols; therefore,for sol destruction (coagulation),the addition of an electrolyte is required.

(D) The ability of an ion to bring about coagulation of a given colloid depends upon both the magnitude and sign of its charge. According to the $Hardy-Schulze$ rule,greater the valence of the flocculating ion added,the greater is its power to cause precipitation.

(A) colloid is a heterogeneous system in which one substance is dispersed as very fine particles in another substance.
$A$ Chlorophyll is a complex molecule (a coordination compound of magnesium) and not a colloidal system.
$B$ Egg white is a sol (colloid of solid in liquid).
$C$ Ruby glass is a solid sol (colloid of solid in solid).
$D$ Milk is an emulsion (colloid of liquid in liquid).
Therefore,chlorophyll is not a colloid.

(B) surfactant (surface active agent) is a molecule that has both a hydrophobic tail and a hydrophilic head,which allows it to reduce surface tension.
$A$ is cetyltrimethylammonium bromide,a cationic surfactant.
$C$ is sodium stearyl sulfate,an anionic surfactant.
$D$ is sodium palmitate,an anionic surfactant.
$B$ is $CH_3-(CH_2)_{14}-CH_2-NH_2$ (hexadecylamine),which is a long-chain primary amine. It does not possess an ionic or highly polar head group capable of forming a stable micelle in water at neutral pH,and thus is not considered a typical surfactant.

(A) The size of colloidal particles generally ranges from $1 \ nm$ to $1000 \ nm$ ($10^{-9} \ m$ to $10^{-6} \ m$).
In terms of millimicrons $(m\mu)$,where $1 \ m\mu = 1 \ nm$,the range is $1 \ m\mu$ to $1000 \ m\mu$.
Given the options provided,the range $1 \ nm$ to $1000 \ nm$ is the standard definition for colloidal systems.

(D) 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).
Gold solution is a negatively charged sol.
Therefore,the coagulating power depends on the valency of the cation.
However,in this specific case,the complex anion $[Fe(CN)_6]^{4-}$ has a high negative charge,but the question refers to the coagulation of a gold sol (which is negative). The effective coagulating ion must be a cation.
Wait,gold sol is typically negative,so it requires a cation for coagulation. Among the given options,$MgCl_2$ provides $Mg^{2+}$,while others provide $Na^+$ or $K^+$.
Actually,$K_4[Fe(CN)_6]$ is often cited in textbooks for specific interactions,but based on the $Hardy-Schulze$ rule for a negative sol,$MgCl_2$ $(Mg^{2+})$ is more effective than $Na^+$ or $K^+$.
Given the standard context of this question,$K_4[Fe(CN)_6]$ is often the intended answer due to the high charge density of the complex ion,but strictly speaking,for a negative sol,$MgCl_2$ is the correct choice. Assuming the question implies the most effective coagulant provided,$MgCl_2$ is the answer.