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

(C) The correct answer is $C$.
Colloidal silica is not a protective colloid.
Protective colloids are lyophilic colloids that prevent the coagulation of lyophobic colloids.
Colloidal silica is typically used as a free-flow agent to assist powder flow.

(A) According to the Hardy-Schulze rule,the coagulating power of an ion is directly proportional to its valency (charge) for the coagulation of a colloidal solution of opposite charge.
For a positively charged colloidal solution,the coagulating power of anions follows the order: $[Fe(CN)_6]^{4-} > [Fe(CN)_6]^{3-} > CO_3^{2-} > Br^-$.
The precipitation (flocculation) value is inversely proportional to the coagulating power.
Therefore,the ion with the lowest charge will have the maximum precipitation value.
Comparing the charges: $Br^-$ $(-1)$,$CO_3^{2-}$ $(-2)$,$[Fe(CN)_6]^{3-}$ $(-3)$,$[Fe(CN)_6]^{4-}$ $(-4)$.
Since $Br^-$ has the minimum charge,it has the maximum precipitation value.

(B) Micelle formation takes place above a particular temperature called Kraft temperature and above a particular concentration called critical micelle concentration $(CMC)$.
Below $CMC$,no micelle formation takes place and the substance does not act as a colloid.
Tyndall effect is the property of scattering of light shown exclusively by colloids.
An aqueous solution of sodium chloride and sugar act as true solutions,so they will never show Tyndall effect.
However,soap solution above $CMC$ forms micelles,which are colloidal particles,and hence it shows Tyndall effect.
Therefore,aqueous solution of soap above critical micelle concentration shows Tyndall effect.

(D) Absorption of ionic species from solution is not responsible for the presence of electric charge on the sol particles.
Charge on the sol particles is primarily due to:
$1$. Electron capture by sol particles during electro-dispersion of metals.
$2$. Preferential adsorption of ionic species from the solution.
$3$. Formation of the Helmholtz electrical double layer.

(A) Hydrophilic sols are lyophilic colloids where the dispersed phase has a strong affinity for the dispersion medium $(H_2O)$.
When a hydrophilic substance is dissolved in water,it interacts with the water molecules,which reduces the cohesive forces between the water molecules at the surface.
Since surface tension is a result of these cohesive forces,the addition of a hydrophilic solute decreases the surface tension of the solvent.
Therefore,the surface tension of a hydrophilic sol is less than that of pure $H_2O$.

(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 colloidal solution ranges between $1 \ nm$ and $1000 \ nm$,which are larger than true solution particles but too small to be seen individually by the naked eye.
The particle size of a suspension is greater than $1000 \ nm$,making them large enough to be seen by the naked eye.
Therefore,the order of particle size is: $\text{Suspension} > \text{Colloidal solution} > \text{True solution}$.

(B) Lyophilic colloids like Gelatin act as protective colloids.
They prevent the coagulation of lyophobic sols by forming a protective layer around them.
Gelatin has a very low gold number,which indicates it is a highly effective protective colloid.

(B) The $As_2S_3$ sol is a negatively charged sol.
According to the Hardy-Schulze rule,the coagulation power of an electrolyte depends on the valency of the coagulating ion (the ion with a charge opposite to that of the sol).
For a negatively charged sol,the coagulating power depends on the charge of the cation.
The cations present are:
$(I) K_2SO_4 \rightarrow K^+ \text{ (charge } +1)$
$(II) CaCl_2 \rightarrow Ca^{2+} \text{ (charge } +2)$
$(III) Na_3PO_4 \rightarrow Na^+ \text{ (charge } +1)$
$(IV) AlCl_3 \rightarrow Al^{3+} \text{ (charge } +3)$
Comparing the charges: $K^+ = Na^+ < Ca^{2+} < Al^{3+}$.
Thus,the increasing order of coagulation power is $I = III < II < IV$.

(C) In the first case,$AgI$ particles adsorb $I^-$ ions from the excess $KI$,forming a negatively charged sol: $(AgI)I^-$.
In the second case,$AgI$ particles adsorb $Ag^+$ ions from the excess $AgNO_3$,forming a positively charged sol: $(AgI)Ag^+$.
When these oppositely charged sols are mixed,they neutralize each other's charge,leading to mutual coagulation.

(A) The gold number is defined as the minimum amount of protective colloid in milligrams that prevents the coagulation of $10 \ mL$ of a gold sol when $1 \ mL$ of a $10\% \ NaCl$ solution is added to it.
Given mass of starch = $0.025 \ g = 25 \ mg$.
Since $25 \ mg$ of starch is required to prevent the coagulation of $10 \ mL$ of gold sol,the gold number of starch is $25$.

(D) According to the $Hardy-Schulze$ rule,the coagulating power of an electrolyte increases with the increase in the magnitude of the charge on the ion used for coagulation.
For a positively charged sol,the coagulating power depends on the charge of the anion.
The order of coagulating power is: $[Fe(CN)_6]^{4-} > PO_4^{3-} > SO_4^{2-} > Cl^{-}$.
Since the flocculation value is inversely proportional to the coagulating power,the ion with the highest charge will have the minimum flocculation value.
Therefore,$[Fe(CN)_6]^{4-}$ has the minimum flocculation value.

(C) The gold number of a lyophilic sol is defined as the minimum amount of the protective colloid in milligrams required to just prevent the coagulation of $10 \, mL$ of a standard gold sol when $1 \, mL$ of a $10 \, \%$ $NaCl$ solution is added to it.
Since the gold number represents the amount of colloid needed to provide protection,a lower gold number indicates that a smaller amount of the substance is required to achieve the same protective effect.
Therefore,the lower the gold number,the greater is the protecting power of the lyophilic colloid.

(C) Lyophilic sols are solvent-loving colloids.
They are quite stable and do not require electrolytes for stability.
They show reversibility,meaning they can be reformed by adding the dispersion medium after evaporation.
Their surface tension is usually lower than that of the dispersion medium.
However,their viscosity is much higher than that of the dispersion medium,making option $C$ the incorrect statement.

(A) $1$. Blood is a negatively charged sol,not a positively charged sol. Therefore,statement $A$ is incorrect.
$2$. Soap solution contains ionic micelles (aggregates of stearate ions) as colloidal particles. Statement $B$ is correct.
$3$. Blood is purified by the process of dialysis,which removes waste products. Statement $C$ is correct.
$4$. Chemical adsorption (chemisorption) involves the formation of chemical bonds,which requires activation energy. Thus,it first increases with temperature and then decreases due to the exothermic nature of the process. Statement $D$ is correct.
Since the question asks for the statement that is not true,the correct option is $A$.

(A) sol is a type of colloidal system where a solid is dispersed in a liquid medium.
Therefore,the correct representation of a sol is $solid \text{ in } liquid$.

(D) According to the Hardy-Schulze rule, the coagulation power of an electrolyte depends on the valency of the ion carrying a charge opposite to that of the colloidal particles.
For a positive sol, the effective coagulating ions are anions.
Coagulation power $\propto$ Valency of the effective ion.
Comparing the valencies of the given anions:
$NO_3^-$ (valency = $1$)
$SO_4^{2-}$ (valency = $2$)
$PO_4^{3-}$ (valency = $3$)
$[Fe(CN)_6]^{4-}$ (valency = $4$)
Since $[Fe(CN)_6]^{4-}$ has the highest valency, it has the maximum coagulation power.

(D) According to the Hardy-Schulze law,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).
Since the sulphur sol is negatively charged,the positive ion is responsible for coagulation.
The valency of the positive ions in the given compounds are:
$K^+$ $(+1)$,
$Ca^{2+}$ $(+2)$,
$Na^+$ $(+1)$,
$Fe^{3+}$ $(+3)$.
According to the Hardy-Schulze law,the greater the valency of the flocculating ion,the greater is its power to cause precipitation.
Therefore,$Fe^{3+}$ ion is the most effective in precipitating the negatively charged sulphur sol.

(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 electrolyte ($HCl$ or $FeCl_3$) acts as a peptizing agent,which adsorbs onto the surface of the precipitate particles,causing them to break down into colloidal-sized particles due to electrostatic repulsion.
Therefore,the correct answer is $Peptization$.

(B) Muddy water contains colloidal clay particles which are negatively charged. $Alum$ $(K_2SO_4 \cdot Al_2(SO_4)_3 \cdot 24H_2O)$ provides $Al^{3+}$ ions. These $Al^{3+}$ ions neutralize the negative charge on the clay particles,causing them to coagulate and settle at the bottom due to gravity.

(A) Starch is a negatively charged colloidal sol.
In the process of electrophoresis,negatively charged particles move towards the positively charged electrode,which is the anode.
Therefore,the colloidal particles of starch move towards the anode.

(A) Surface active agents (surfactants) are classified based on the charge of the polar head group in the aqueous solution.
$A$. Sodium dodecyl benzene sulphonate $(C_{12}H_{25}-C_6H_4-SO_3^-Na^+)$ dissociates to give a large anionic part $(C_{12}H_{25}-C_6H_4-SO_3^-)$,hence it is an anionic surfactant.
$B$. Cetyl trimethyl ammonium chloride $([C_{16}H_{33}N(CH_3)_3]^+Cl^-)$ dissociates to give a large cationic part,hence it is a cationic surfactant.
$C$. Cetyl pyridinium chloride $([C_{16}H_{33}NC_5H_5]^+Cl^-)$ also dissociates to give a large cationic part,hence it is a cationic surfactant.
Therefore,sodium dodecyl benzene sulphonate is the correct anionic surfactant.

(B) The gold number is defined as the minimum amount of protective colloid in $mg$ required to prevent the coagulation of $10 \ mL$ of a gold sol when $1 \ mL$ of $10 \% \ NaCl$ solution is added.
Given: Gold number of albumin = $0.09 \ mg$.
This means $0.09 \ mg$ of albumin protects $10 \ mL$ of gold sol from $1 \ mL$ of $10 \% \ NaCl$.
We need to protect $40 \ mL$ of gold sol from $4 \ mL$ of $10 \% \ NaCl$.
Since the amount of gold sol is $4$ times the standard volume $(40 \ mL / 10 \ mL = 4)$,the amount of albumin required will be $4 \times 0.09 \ mg = 0.36 \ mg$.

(C) Potash alum,with the chemical formula $K_2SO_4 \cdot Al_2(SO_4)_3 \cdot 24H_2O$,is widely used for the purification of water.
It acts as a coagulant,which helps in settling down the suspended impurities in water.

(C) $1$. $A$ liquid that scatters light exhibits the $Tyndall$ effect,which is a characteristic property of colloids.
$2$. Colloidal particles are small enough to pass through ordinary filter paper without leaving a residue.
$3$. $A$ suspension would leave a residue on filter paper,and a true solution does not scatter light.
$4$. Therefore,the liquid is a $Colloidal$ $sol$.

(A) Colloidal solutions are heterogeneous in nature,not homogeneous. Therefore,the statement that 'Colloidal sols are homogeneous' is incorrect. Colloids do carry charge (positive or negative),they exhibit the Tyndall effect,and their particle size range is indeed between $10 \ \mathring{A}$ and $1000 \ \mathring{A}$ ($1 \ \text{nm}$ to $1000 \ \text{nm}$).

(A) The particle size in a true solution is less than $1 \, nm$ $(1 \, m\mu)$.
In a colloidal solution,the particle size ranges from $1 \, nm$ to $1000 \, nm$ ($1 \, m\mu$ to $1000 \, m\mu$).
In a suspension,the particle size is greater than $1000 \, nm$ ($1000 \, m\mu$ or $1 \, \mu m$).
Since $300 \, m\mu$ falls within the range of a colloidal solution $(1 \, m\mu - 1000 \, m\mu)$,but the question asks for particles greater than $300 \, m\mu$,both colloidal particles (up to $1000 \, m\mu$) and suspension particles (greater than $1000 \, m\mu$) satisfy this condition.
However,in standard chemistry classification,suspensions are defined as having particles larger than $1000 \, nm$,while colloids are between $1 \, nm$ and $1000 \, nm$.
Given the options,a suspension is the category where particles are characteristically large and definitely exceed $300 \, m\mu$.

(C) Colloidal systems are classified based on the physical state of the dispersed phase and the dispersion medium.
$1$. Emulsion: Liquid in liquid (e.g.,milk). Curd is a gel.
$2$. Foam: Gas in liquid (e.g.,whipped cream). Fog is an aerosol (liquid in gas).
$3$. Aerosol: Solid or liquid in gas. Smoke is a solid in gas,which is a type of aerosol.
$4$. Solid sol: Solid in solid (e.g.,colored glass). Cake is a foam (gas in solid).
Therefore,the correct match is $C$.

(D) In a colloidal system,the size of the dispersed phase particles typically ranges from $1 \ nm$ to $1000 \ nm$.
Converting these values to meters,we get $1 \times 10^{-9} \ m$ to $1000 \times 10^{-9} \ m$,which simplifies to $10^{-9} \ m$ to $10^{-6} \ m$.
Therefore,the correct range is $10^{-9} \ m$ to $10^{-6} \ m$.

(C) The $CMC$ stands for $Critical \text{ } Micelle \text{ } Concentration$.
At this specific concentration,the surface active molecules (surfactants) associate to form clusters known as micelles.
Therefore,at $CMC$,the surface active molecules form aggregates.

(C) In a colloidal system,when the dispersion medium is a gas,the colloid is classified as an $Aerosol$.
Examples include fog,mist,and clouds,where liquid droplets are dispersed in air (gas).

(D) Macromolecular colloids are substances that have large molecular masses and form colloidal solutions when dispersed in a suitable solvent. Examples include polymers like $Nylon$,$Plastic$,and $Rubber$.
Soap,on the other hand,is an example of an associated colloid (micelle) because it forms aggregates of molecules when its concentration exceeds the Critical Micelle Concentration $(CMC)$.

(C) Hydrophilic sols (lyophilic sols) are solvent-loving and are quite stable.
$1$. They have high viscosity and low surface tension compared to the dispersion medium (water).
$2$. They are reversible in nature,meaning they can be reformed by simply mixing the dispersed phase and dispersion medium after coagulation.
$3$. They can be prepared in high concentrations.
$4$. The charge on the particles is not fixed; it depends on the $pH$ of the medium.
Therefore,the statement that 'viscosity and surface tension are nearly the same as that of water' is incorrect,as hydrophilic sols generally have higher viscosity than water.

(A) Fog is a colloidal system where liquid droplets are dispersed in a gas (air).
Therefore,it is classified as a liquid aerosol,which is defined as liquid dispersed in gas.

(C) Hydrophilic sols are those in which the dispersed phase has a strong affinity for the dispersion medium (usually water).
Starch,proteins,and gums are examples of substances that form hydrophilic sols.
Barium sulphate,arsenious sulphide,and silver iodide are examples of hydrophobic sols,where the dispersed phase has little or no affinity for the dispersion medium.

(D) Hydrophilic sols are stable due to two main factors: $1.$ The charge on the particles and $2.$ The layer of dispersion medium (solvation) surrounding the particles.
Between the given options,the presence of a layer of dispersion medium (solvation) is a primary factor that prevents the particles from aggregating,thus providing stability.

(A) Macromolecular colloids are substances that have large molecular masses and form colloidal solutions when dispersed in a suitable solvent.
Examples include proteins,starch,cellulose,and synthetic polymers like rubber in benzene.
Soap + water forms associated colloids (micelles).
Milk is an emulsion.
Therefore,both protein in water and rubber in benzene are examples of macromolecular colloids. However,in standard chemistry textbooks,protein is the most common example cited for macromolecular colloids.

(C) The critical micelle concentration $(CMC)$ is the concentration above which micelles are formed in a colloidal solution.
If the concentration of the soap solution is below the $CMC$,the soap molecules exist as individual ions or molecules,forming a true solution.
Since the given concentration $(10^{-4} \ mol \ L^{-1})$ is less than the $CMC$ $(10^{-3} \ mol \ L^{-1})$,the soap will exist as a true solution.

(A) Lyophilic sols are solvent-attracting colloids. When a lyophilic substance is dissolved in a solvent like $H_2O$,the surface tension of the resulting sol is generally lower than that of the pure solvent $(H_2O)$. This is because the dispersed phase particles accumulate at the surface,reducing the surface energy.

(A) The critical micelle concentration $(CMC)$ is defined as the specific concentration of a surfactant above which the formation of micelles occurs spontaneously in a solution. Below this concentration,the surfactant exists primarily as individual molecules or ions. Once the $CMC$ is reached,the molecules aggregate to form micelles.

(B) Micelles are clusters or aggregated particles formed by surface-active agents (surfactants) in solution above a particular concentration called the $Critical \text{ } Micelle \text{ } Concentration \text{ } (CMC)$.
These are classified as $Associated \text{ } Colloids$ because they behave as normal strong electrolytes at low concentrations but exhibit colloidal behavior at higher concentrations due to the formation of aggregated particles.

(B) Lyophilic colloids are solvent-loving colloids.
$1$. They have a high affinity for the dispersion medium,which leads to extensive hydration of the particles.
$2$. Their viscosity is much higher than that of the dispersion medium.
$3$. They are generally stable and do not migrate significantly in an electric field unless they carry a charge.
$4$. Their particles are often too small to be detected by an ultramicroscope.
Therefore,the most characteristic property among the given options is that they undergo extensive hydration.

(C) Colloids are classified based on:
$1$. Physical state of dispersed phase and dispersion medium.
$2$. Nature of interaction between dispersed phase and dispersion medium (Lyophilic and Lyophobic).
$3$. Type of particles of the dispersed phase (Multimolecular,Macromolecular,and Associated colloids).
Surface tension is a property of liquids and is not a criterion for the classification of colloidal particles.

(B) Soap molecules consist of a long hydrocarbon chain (hydrophobic tail) and a polar head (hydrophilic head).
When soap is added to water,the hydrophobic tails cluster together to form a micelle,trapping oil and grease inside the non-polar core.
The hydrophilic heads remain on the outside,interacting with the water,which allows the grease to be washed away.
Therefore,oil and grease dissolve in the hydrophobic (non-polar) center of the micelle.

(B) Bredig's arc method is used for the preparation of colloidal sols of metals like $Au$,$Ag$,and $Pt$.
In this method,an electric arc is struck between electrodes of the metal immersed in a dispersion medium.
$Fe$ (Iron) cannot be prepared by this method because it is highly reactive and tends to form oxides or hydroxides rather than a stable colloidal sol of the metal itself.

(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,$Fe(OH)_3$ precipitate adsorbs $Fe^{3+}$ ions from the added $HCl$ electrolyte,which causes the particles to disperse into the medium,forming a colloidal solution.

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

(C) Bredig's arc method is a specialized technique used for the preparation of colloidal sols of metals like gold,silver,and platinum. In this method,an electric arc is struck between electrodes of the metal immersed in a dispersion medium (water) cooled by ice. The intense heat vaporizes the metal,which then condenses to form colloidal particles.

(C) The process of separating colloidal particles from crystalloids (molecular dimensions) by using an electric field is known as $Electrodialysis$.
In this process,the rate of dialysis is increased by applying an electric field across the membrane.