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

(A) Silver nanoparticles $(AgNPs)$ are well-known for their potent antimicrobial properties. They effectively disrupt the cell membrane and metabolic processes of bacteria like $E. coli$,making them highly efficient for water purification and disinfection.

(C) Multimolecular colloids are formed by the aggregation of a large number of atoms or smaller molecules with diameters less than $1 \ nm$.
In the case of sulphur sol,the particles consist of thousands of $S_8$ molecules.
Starch,cellulose,and plastics are examples of macromolecular colloids,as they consist of large molecules with high molecular masses.

(A) Fog is a type of colloid in which a liquid is dispersed in a gas.
This type of colloidal system is classified as an $Aerosol$.

(D) Macromolecular colloids are substances that have very large molecular masses and form colloidal solutions when dispersed in a suitable solvent.
Examples include naturally occurring polymers like starch,cellulose,proteins,and synthetic polymers like $Nylon$,$polythene$,and $polystyrene$.
Soap and detergents are associated colloids (micelles),while $S_8$ sulphur molecules are multimolecular colloids.
Therefore,$Nylon$ is classified as a macromolecular colloid.

(A) Cheese is a type of colloid known as a gel.
In a gel,the dispersed phase is a liquid and the dispersion medium is a solid.
According to the provided table,row $1$ represents a system where the dispersed phase is liquid and the dispersion medium is solid.
Therefore,the correct option is $1$.

(C) Multimolecular colloids are formed by the aggregation of a large number of atoms or smaller molecules with diameters less than $1 \ nm$.
Sulfur sol,which consists of a large number of $S_8$ molecules,is a classic example of a multimolecular colloid.
Soap and synthetic polymers like Polythene and Nylon are examples of associated colloids and macromolecular colloids,respectively.

(D) In macromolecular colloids,the molecules of the dispersed phase are sufficiently large in size (macro) to be of colloidal dimensions.
Examples of macromolecular colloids include starch,cellulose,proteins,polythene,nylon,and plastics.
Soap is an example of an associated colloid (micelle),not a macromolecular colloid.

(D) In lyophilic colloids,the particles of the dispersed phase have a great affinity for the dispersion medium.
They are reversible and self-stabilized colloids.
Addition of a large amount of electrolytes is required to cause precipitation or coagulation of lyophilic sols,whereas lyophobic colloids are easily coagulated by small amounts of electrolytes.

(D) According to the $Schulze-Hardy$ rule,the coagulating power of an ion is directly proportional to its valency (charge) for the precipitation of a sol.
For a positive sol,the coagulating power depends on the magnitude of the negative charge of the anion.
The order of coagulating power is $\left[Fe(CN)_6\right]^{4-} > PO_4^{3-} > SO_4^{2-} > Cl^{-}$.
Therefore,the anion with the lowest valency,$Cl^{-}$,has the lowest coagulating power.

(C) Milk is an emulsion,which is a type of colloid where a $liquid$ is dispersed in another $liquid$.
Specifically,it consists of $liquid$ butterfat globules dispersed within a water-based solution.

(C) Soap lather is a type of colloidal system known as $Foam$.
In this system,a gas is dispersed in a liquid medium.

(A) Fog is a type of colloid known as an aerosol where a liquid is dispersed in a gas.
Therefore,the dispersed phase is liquid and the dispersion medium is gas.
Thus,option $(A)$ is the correct answer.

(C) Lyophilic colloids are characterized by a strong affinity between the dispersed phase and the dispersion medium.
They are stable and are not easily precipitated by small amounts of electrolytes; a large amount of electrolyte is required to cause coagulation (salting out).
They are reversible in nature,meaning they can be reformed after evaporation of the dispersion medium.
They are not easily visible under an ultramicroscope due to the small size and high solvation of particles.

(D) According to the Hardy-Schulze rule,the coagulating power of an ion is directly proportional to the magnitude of the charge on the ion of opposite sign to that of the colloidal particle.
For a negatively charged sol,the coagulating power depends on the positive charge of the added cation.
The given cations are $Ba^{2+}$ and $Al^{3+}$.
Since the charge on $Al^{3+}$ $(+3)$ is greater than the charge on $Ba^{2+}$ $(+2)$,$Al^{3+}$ has greater coagulating power.

(B) Multimolecular colloids are formed by the aggregation of a large number of atoms or smaller molecules with diameters less than $1 \ nm$.
$S_8$ (sulfur) molecules aggregate to form particles of colloidal size,making it a classic example of a multimolecular colloid.
Starch,cellulose,and plastic are examples of macromolecular colloids.

(A) Soap and detergents are examples of associative colloids (micelles).
They consist of a long hydrocarbon chain which is hydrophobic (water-repelling) and a polar ionic group (like $-COO^-$ or $-SO_3^-$) which is hydrophilic (water-attracting).
Therefore,the correct answer is $A$.

(B) multi-molecular colloid is formed by the aggregation of a large number of atoms or smaller molecules with diameters less than $1 \ nm$. $Gold \ sol$ is a classic example of a multi-molecular colloid.
$Nylon$ and $Cellulose$ are examples of macromolecular colloids.
$Soap$ is an example of an associated colloid (micelle).

(B) colloidal sol is formed by substances that are macromolecules or aggregates of molecules with sizes in the range of $1 \ nm$ to $1000 \ nm$.
$1$. Common salt $(NaCl)$,glucose,and ammonium sulphate are electrolytes or small molecules that form true solutions in water.
$2$. Starch is a macromolecule that,when dispersed in water,forms a lyophilic colloidal sol.
Therefore,the correct option is $B$.

(C) Hydrophobic sols are those in which the dispersed phase has little or no affinity for the dispersion medium. These are also known as lyophobic sols.
Metal sulphides (e.g.,$As_2S_3$) are classic examples of hydrophobic (lyophobic) sols.
Rubber in benzene,cellulose acetate in acetone,and starch in water are examples of hydrophilic (lyophilic) sols,as they have a strong affinity for the dispersion medium.

(B) Colloidal particles carry an electric charge.
$As_2S_3$ (Arsenic sulfide) is a well-known negatively charged sol.
Clay is also a negatively charged sol.
Congo red is a dye that forms a negatively charged sol.
Haemoglobin is a positively charged sol because it is a protein that exists in a positively charged state at a $pH$ below its isoelectric point.
Therefore,Haemoglobin is not a negatively charged sol.

(B) The movement of colloidal particles under 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.
$Brownian \ motion$ refers to the random zig-zag movement of particles.
$Electroosmosis$ refers to the movement of the dispersion medium under an electric field.
$Dialysis$ is a process of removing impurities from a colloidal solution.

(B) Coagulation is the process of aggregating colloidal particles to form a precipitate.
$1$. Electrophoresis causes particles to move towards oppositely charged electrodes and discharge,leading to coagulation.
$2$. Mixing two oppositely charged sols leads to mutual coagulation.
$3$. Boiling increases the kinetic energy of particles,causing them to collide and overcome the protective layer,leading to coagulation.
$4$. Adding excess solvent (dilution) does not cause coagulation; in fact,it often stabilizes the sol by increasing the distance between particles.

(D) According to the Hardy-Schulze rule,the coagulating power of an ion is directly proportional to the magnitude of its charge.
For a positively charged sol,the coagulating power depends on the valency of the anion.
The higher the negative charge on the anion,the greater is its coagulating power.
The charges on the given anions are:
$A: SO_4^{2-}$ (charge $-2$)
$B: Cl^{-}$ (charge $-1$)
$C: PO_4^{3-}$ (charge $-3$)
$D: [Fe(CN)_6]^{4-}$ (charge $-4$)
Since the ion $\left[Fe(CN)_6\right]^{4-}$ has the highest magnitude of negative charge $(-4)$,it exhibits the maximum power of coagulation for a positively charged sol.

(A) Colloids are classified based on the charge on the dispersed phase particles.
$1$. Negatively charged sols include metal sulphides (e.g.,$As_2S_3$),acidic dyes (e.g.,Eosin,Congo red),and starch.
$2$. Positively charged sols include metal hydroxides (e.g.,$Fe(OH)_3$),basic dyes (e.g.,Methylene blue),and proteins like Haemoglobin.
$3$. Titanium oxide $(TiO_2)$ is generally considered a positively charged sol.
Therefore,Eosin is a negatively charged sol.

(A) According to the Hardy-Schulze rule,the coagulating power of an ion is directly proportional to the magnitude of its charge.
For the precipitation of a positive sol,the anion with the highest negative charge will have the maximum coagulating power.
Comparing the charges: $\left[Fe(CN)_6\right]^{4-}$ has a charge of $-4$,$PO_4^{3-}$ has $-3$,$SO_4^{2-}$ has $-2$,and $Cl^{-}$ has $-1$.
Therefore,$\left[Fe(CN)_6\right]^{4-}$ has the maximum coagulating power.

(A) Haemoglobin in blood is a positively charged sol.
Starch sol,gelatin sol,and silver $(Ag)$ sol are examples of negatively charged sols.

(A) The size of colloidal particles typically ranges from $1 \ nm$ to $1000 \ nm$ ($10^{-9} \ m$ to $10^{-6} \ m$).

(A) Colloidal sols are classified based on the charge on the dispersed phase particles.
$CdS$ (Cadmium sulfide) is a well-known example of a negatively charged sol.
In contrast,metal oxides and hydrated metal oxides like $Al_2O_3 \cdot xH_2O$,$CrO_3 \cdot xH_2O$,and $TiO_2$ are typically positively charged sols.

(A) The charge on colloidal particles depends on the nature of the dispersed phase and the dispersion medium.
$1$. Sol of clay is a negatively charged sol.
$2$. $Fe_2O_3 \cdot xH_2O$ is a positively charged sol.
$3$. $TiO_2$ sol is a positively charged sol.
$4$. Haemoglobin is a positively charged sol.
Therefore,the correct option is $A$.

(A) According to the Hardy-Schulze rule,the precipitating power of an ion is directly proportional to its valency (charge).
Greater the valency of the flocculating ion,the greater will be its power to cause coagulation.
Comparing the charges: $Al^{3+}$ $(+3)$ > $Ba^{2+}$ $(+2)$ > $Na^{+}$ $(+1)$.
Therefore,the correct decreasing order is $Al^{3+} > Ba^{2+} > Na^{+}$.

(D) According to the Hardy-Schulze rule,the precipitating power of an ion is directly proportional to its valency (charge).
Greater the magnitude of the charge on the ion,the higher is its precipitating power.
Comparing the charges: $Na^{+}$ $(+1)$,$Cu^{2+}$ $(+2)$,$Al^{3+}$ $(+3)$,$SO_4^{2-}$ $(-2)$.
Since $Al^{3+}$ has the highest magnitude of charge $(+3)$,it has the highest precipitating power.

(C) Electrophoresis is a phenomenon in which colloidal particles move towards oppositely charged electrodes under the influence of an electric field.
Since the direction of movement of the particles depends on the nature of the charge they carry,this technique is used to determine the charge on colloidal particles.

(D) The Tyndall effect is the phenomenon in which the particles in a colloid scatter the beams of light that are directed at them. This occurs because the size of colloidal particles is comparable to the wavelength of light,allowing them to scatter the light in all directions,making the path of the light beam visible.

(A) According to the Hardy-Schulze rule,the precipitating power of an ion is directly proportional to its valency.
Since the precipitating power increases with the increase in the magnitude of the charge on the ion,the ion with the lowest valency will have the least precipitating power.
Comparing the valencies: $Cl^{-}$ $(1)$,$SO_{4}^{2-}$ $(2)$,$Mg^{2+}$ $(2)$,$Al^{3+}$ $(3)$.
Therefore,$Cl^{-}$ has the least precipitating power.

(A) Multimolecular colloids are formed by the aggregation of a large number of atoms or smaller molecules (diameter $< 1 \ nm$).
Silver sol is a classic example of a multimolecular colloid,where many silver atoms aggregate to form particles of colloidal size.
Rubber,proteins,and polyvinyl alcohol are examples of macromolecular colloids,where the molecules themselves are of colloidal dimensions.

(D) The precipitation power of an electrolyte increases with the charge of the flocculating ion. This is explained by the $Hardy-Schulze$ rule,which states that the greater the valence (charge) of the flocculating ion added,the greater is its power to cause precipitation.

(C) The colour of a colloidal solution depends on the wavelength of the light scattered by the dispersed particles,which in turn depends on the size and the nature of the particle.
The blue colour of water in the sea is primarily due to the scattering of light by water molecules.

(D) The classification of colloids based on the physical state of the dispersed phase and dispersion medium is as follows:
$1$. Foam rubber is a solid sol (gas in solid).
$2$. Froth is a foam (gas in liquid).
$3$. Gelatin is a gel (liquid in solid).
$4$. Hair cream is an emulsion (liquid in liquid).
Therefore,the correct option is $D$.

(C) gel is a colloidal system in which a liquid is dispersed in a solid.
Cheese,butter,and jellies are examples of gels.
Milk is an emulsion,which is a colloidal system where a liquid is dispersed in another liquid.

(A) In an "oil in water" $(O/W)$ emulsion,water acts as the dispersion medium and oil acts as the dispersed phase.
Since water is the dispersion medium,the emulsion can conduct electricity.
When a small amount of an electrolyte is added to an $O/W$ emulsion,the conducting power increases significantly because the dispersion medium (water) is a polar solvent capable of dissolving electrolytes to form ions.
Therefore,the correct statement is that basic metal sulfates (or proteins/soaps) are often used as emulsifiers to stabilize $O/W$ emulsions.

(B) Soap molecules have a hydrophobic hydrocarbon tail and a hydrophilic ionic head.
When soap is added to an oily or greasy part of cloth,the hydrophobic hydrocarbon tail dissolves in the oil,while the hydrophilic head remains in the water.
This arrangement forms a micelle,where the oil droplet is surrounded by soap molecules.
Consequently,the oil is emulsified and washed away by the stream of water.

(C) An emulsion is a colloidal system in which both the dispersed phase and the dispersion medium are liquids.
Milk is a classic example of an emulsion where liquid fat is dispersed in water.
Butter is a gel (solid-in-liquid),jellies are gels (liquid-in-solid),and mist is an aerosol (liquid-in-gas).
Therefore,the correct answer is $C$.

(B) Both $SEM$ (Scanning Electron Microscopy) and $TEM$ (Transmission Electron Microscopy) are used for the determination of particle size and morphology. However,$TEM$ is generally considered the standard technique for precise particle size measurement at the nanoscale. Given the options,both $A$ and $B$ are technically correct,but $TEM$ is the most common answer in this context.

(A) Nanomaterials are classified based on the number of dimensions that are outside the nanoscale range $(< 100 \ nm)$.
$1$. $0-D$ nanomaterials: All three dimensions are in the nanoscale range (e.g.,nanoparticles,quantum dots,nanoshells).
$2$. $1-D$ nanomaterials: Two dimensions are in the nanoscale range (e.g.,nanotubes,nanowires,fibres).
$3$. $2-D$ nanomaterials: One dimension is in the nanoscale range (e.g.,thin films,graphene).
Since nanoshells have all three dimensions less than $100 \ nm$,they are classified as $0-D$ nanomaterials.

(D) Quantum dots are zero-dimensional $(0D)$ nanostructures because all three dimensions are restricted to the nanoscale $(1-100 \ nm)$.
In contrast,nanotubes and fibres are one-dimensional $(1D)$ nanostructures,and thin films are two-dimensional $(2D)$ nanostructures.

(C) nanomaterial with one dimension less than $100 \ nm$ is classified as a two-dimensional nanostructure.
Thin films have one dimension in the nanoscale range,while the other two dimensions are much larger.
Therefore,thin films are the correct answer.

(B) Nanostructures are classified based on their dimensions in the nanoscale range $(1-100 \ nm)$:
$1$. Zero-dimensional $(0D)$ nanostructures: All three dimensions are in the nanoscale (e.g.,Quantum dots,Nanoparticles).
$2$. One-dimensional $(1D)$ nanostructures: Two dimensions are in the nanoscale (e.g.,Nanowires,Nanotubes).
$3$. Two-dimensional $(2D)$ nanostructures: One dimension is in the nanoscale (e.g.,Thin films,Layers,Coatings).
Therefore,Thin films are examples of two-dimensional nanostructures.

(C) Nanostructures are classified based on their dimensions. $0-D$ nanostructures have all three dimensions in the nanometer range,such as $Nanoparticles$. $1-D$ nanostructures have two dimensions in the nanometer range,such as $Nanorods$ and $Nanowires$. $2-D$ nanostructures have one dimension in the nanometer range,such as $Thin \text{ } films$.

(A) one-dimensional nanostructure is defined as a structure where two dimensions are in the nanometer range and one dimension is larger.
Nanowires,nanotubes,and fibres are examples of one-dimensional nanostructures.
Nano shells are considered zero-dimensional nanostructures because all three dimensions are in the nanometer range.
Therefore,nano shells are not an example of a one-dimensional nanostructure.