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

(A) Medicines are more effective in the $Colloidal$ state because they have a larger surface area in this state.
Due to the larger surface area,they are easily assimilated or absorbed by the body tissues.

(A) colloidal system where a gas is the dispersed phase and a liquid is the dispersion medium is known as foam. Examples include whipped cream and soap lather.

(C) colloidal solution is a heterogeneous mixture where the particle size ranges between $1 \ nm$ and $1000 \ nm$.
$NaCl$ solution is a true solution because $NaCl$ dissolves completely in water to form a homogeneous mixture with particle sizes less than $1 \ nm$.
Smoke,ink,and blood are examples of colloidal systems.

(C) Brownian movement is the continuous,random,zig-zag motion of colloidal particles in a dispersion medium. Since this motion is related to the movement and kinetic energy of the particles,it is considered a kinetic property of colloids.

(D) Volume of gold dispersed in $1 \, L$ of water $= \frac{\text{mass}}{\text{density}} = \frac{1.9 \times 10^{-4} \, g}{19 \, g/cm^3} = 1 \times 10^{-5} \, cm^3$.
Radius of a gold sol particle $= 10 \, nm = 10^{-6} \, cm$.
Volume of one spherical particle $= \frac{4}{3} \pi r^3 = \frac{4}{3} \times 3.14 \times (10^{-6} \, cm)^3 \approx 4.19 \times 10^{-18} \, cm^3$.
Total number of gold particles in $1 \, L = \frac{1 \times 10^{-5} \, cm^3}{4.19 \times 10^{-18} \, cm^3} \approx 2.38 \times 10^{12}$.
Since $1 \, L = 1000 \, cm^3 = 10^{21} \, nm^3$,the number of particles per $nm^3 = \frac{2.38 \times 10^{12}}{10^{21}} = 2.38 \times 10^{-9}$.
Note: Re-evaluating the question's intended units,if the question asks for particles per $cm^3$ or if the volume conversion was intended differently,the provided options suggest a calculation error in the original problem statement. Based on standard calculations,the closest magnitude is $2.4 \times 10^6$ if the volume was $1 \, cm^3$ instead of $1 \, L$.

(A) The Critical Micelle Concentration $(CMC)$ decreases as the length of the hydrophobic hydrocarbon chain increases.
Longer hydrocarbon chains increase the hydrophobic effect,making micelle formation more favorable at lower concentrations.
Comparing the chain lengths:
Option $A$ has a $16$-carbon chain $(C_{16})$.
Option $B$ has a $12$-carbon chain $(C_{12})$.
Option $C$ has a $7$-carbon chain $(C_7)$.
Option $D$ has a $12$-carbon chain $(C_{12})$.
Since option $A$ has the longest hydrocarbon chain,it will form micelles at the lowest concentration.

(C) An emulsion is a colloidal system in which both the dispersed phase and the dispersion medium are liquids.
$O/W$ (Oil in Water) emulsions have oil as the dispersed phase and water as the dispersion medium.
$W/O$ (Water in Oil) emulsions have water as the dispersed phase and oil as the dispersion medium.
Milk is an example of $O/W$ emulsion.
Cold cream is an example of $W/O$ emulsion.
Vanishing cream is an example of $O/W$ emulsion.
Butter is a $W/O$ emulsion (water dispersed in fat),not $O/W$. Therefore,the incorrect match is $C$.

(A) Hair cream is a colloidal system where a liquid is dispersed in another liquid or a solid. Specifically,it is classified as an $Emulsion$ where the dispersed phase and the dispersion medium are both liquids.

(A) 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,the greater is its coagulating power.
The anions present in the given electrolytes are:
$A) PO_4^{3-}$,$B) NO_3^-$,$C) Cl^-$,$D) SO_4^{2-}$.
Since the phosphate ion $(PO_4^{3-})$ has the highest valency $(-3)$,it is the most effective in coagulating the positively charged ferric hydroxide sol.

(A) The surface tension of a lyophilic sol is generally lower than that of the dispersion medium (which is $H_2O$ in aqueous sols).

(D) According to the $Hardy-Schulze$ rule,the coagulating power of an ion depends on the magnitude of the charge carried by the ion.
Greater the valence of the flocculating ion added,the greater is its power to cause precipitation.
The sign of the charge on the ion must be opposite to that of the colloidal particles to cause coagulation.
Therefore,the coagulating power depends on both the magnitude and the sign of the charge.

(D) Gold sol is a negatively charged sol. According to the Hardy-Schulze rule,the coagulating power of an electrolyte depends on the valency of the oppositely charged ion (cation in this case).
Greater the valency of the flocculating ion,greater is its coagulating power.
The cations provided by the electrolytes are:
$A: K^+$ (valency $1$)
$B: K^+$ (valency $1$)
$C: K^+$ (valency $1$)
$D: Mg^{2+}$ (valency $2$)
Since $Mg^{2+}$ has a higher valency than $K^+$,$MgCl_2$ is the most effective electrolyte for the coagulation of negatively charged gold sol.

(C) Colloidal particles are aggregates of molecules or ions. Due to their large size,the number of particles in a colloidal solution is very small compared to a true solution of the same concentration. Since osmotic pressure is a colligative property that depends on the number of particles,colloidal solutions exhibit very low osmotic pressure.

(C) The protective power of a colloid is inversely proportional to its gold number.
Lower gold number implies higher protective power.
Given gold numbers: $A = 0.50, B = 0.01, C = 0.10, D = 0.005$.
Arranging in increasing order of gold numbers: $D (0.005) < B (0.01) < C (0.10) < A (0.50)$.
Therefore,the order of protective power is $A < C < B < D$.

(A) Milk is a natural colloid in which fat globules are dispersed in water. Therefore,it is classified as an emulsion of fat in water. Proteins (like casein) act as emulsifying agents to stabilize the emulsion.

(A) The $Hardy-Schulze$ rule states that 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).
According to this rule,the greater the valency of the flocculating ion,the greater is its coagulating power.
Therefore,the correct answer is $Hardy-Schulze$.

(B) 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).
$2$. Gel: Liquid in solid (e.g.,Butter,Jelly).
$3$. Aerosol: Solid or liquid in gas (e.g.,Smoke,Fog).
$4$. Foam: Gas in liquid (e.g.,Whipped cream).
Comparing these with the options,$B$ (Gel - Butter) is the only correctly matched pair.

(D) Lyophilic sols are solvent-loving colloids.
They have a strong affinity between the dispersed phase and the dispersion medium.
Because of this strong interaction,they are highly stable and are known as self-stabilizing sols.
They are reversible in nature and are typically formed by organic substances like starch,gum,and proteins.

(A) The gold number is defined as the minimum weight 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.
Since the gold number is inversely proportional to the protective power of the colloid,a higher protective power implies a lower gold number.

(D) gel is a semi-solid colloidal system where a liquid is dispersed in a solid medium.
$1$. Gels can be formed by both organic substances (e.g.,gelatin,agar) and inorganic substances (e.g.,silica gel).
$2$. They are classified as colloidal systems.
$3$. Many gels exhibit elasticity and can be reversible (e.g.,gelatin) or irreversible depending on their nature.
Therefore,all the given statements are correct.

(D) Gelatin is a protein-based substance that forms a colloidal solution with water.
$1$. It is $Lyophilic$ because it has a strong affinity for the dispersion medium (water).
$2$. It is $Reversible$ because the sol can be converted back to a gel and vice versa.
$3$. It is $Hydrophilic$ because it has a strong affinity for water.
Therefore,all the given terms correctly describe the colloidal solution of gelatin.

(C) gold sol is a colloidal system where gold particles (solid) are dispersed in water (liquid).
Since gold is a metal,it does not have a strong affinity for the dispersion medium (water),making it a lyophobic colloid.
Therefore,the dispersed phase is $Solid$,the dispersion medium is $Liquid$,and the nature is $Lyophobic$.

(C) colloidal solution is a heterogeneous mixture where the particle size ranges between $1 \ nm$ and $1000 \ nm$.
$NaCl$,glucose,and $Ba(NO_3)_2$ are electrolytes or non-electrolytes that dissolve in water to form true solutions because their particle sizes are smaller than $1 \ nm$.
Starch is a macromolecule with a large molecular mass,and when mixed with water,it forms a colloidal solution.

(B) 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).
$As_2S_3$ is a negatively charged sol.
Therefore,the coagulating power depends on the valency of the cation.
Greater the valency of the cation,higher is the coagulating power and lower is the coagulation value.
The valencies of the cations are: $Be^{2+}$ $(2)$,$Al^{3+}$ $(3)$,$K^+$ $(1)$,$Na^+$ $(1)$.
Since $Al^{3+}$ has the highest valency $(3)$,it has the highest coagulating power and thus the lowest coagulation value.
Therefore,$AlCl_3$ is the correct answer.

(C) Colloidal systems are classified based on the physical state of the dispersed phase and the dispersion medium.
$1$. Emulsion: Liquid dispersed in liquid (e.g.,Milk).
$2$. Foam: Gas dispersed in liquid (e.g.,Whipped cream).
$3$. Aerosol: Solid or liquid dispersed in gas (e.g.,Smoke is solid in gas,Fog is liquid in gas).
$4$. Solid sol: Solid dispersed in solid (e.g.,Colored gemstones).
Therefore,the pair $Aerosol - Smoke$ is correct.

(D) micelle is an aggregate of surfactant molecules dispersed in a liquid colloid.
Sodium stearate $(C_{17}H_{35}COONa)$ is a soap that acts as a surfactant.
In a concentrated solution,sodium stearate molecules form micelles where the hydrophobic tails point inward and the hydrophilic heads point outward.
Therefore,a concentrated solution of sodium stearate is an example of a micelle.

(D) The gold number is defined as the minimum amount of protective colloid in milligrams 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.
Given: Mass of starch = $0.25 \ g = 250 \ mg$.
Since $250 \ mg$ of starch is required to prevent coagulation in $10 \ mL$ of gold sol,the gold number of starch is $250$.

(A) Fog is a colloidal system in which a liquid (water droplets) is dispersed in a gas (air). This type of colloid is classified as an aerosol.

(C) The process of separating the particles of crystalloids from a colloid by means of diffusion through a suitable membrane is known as $Dialysis$. Since colloidal particles cannot pass through a parchment paper or cellophane membrane,they are retained while the impurities (crystalloids) pass through,thus purifying the colloid.

(C) $1$. Iron $(III)$ hydroxide sol is positively charged,and gold sol is negatively charged.
$2$. According to the Hardy-Schulze rule,the coagulating power of an electrolyte depends on the valency of the ion carrying a charge opposite to that of the colloidal particle.
$3$. For negatively charged gold sol,$Mg^{2+}$ ions (from $MgCl_2$) are more effective than $Cl^-$ ions. For positively charged iron $(III)$ hydroxide sol,$SO_4^{2-}$ ions (from $Na_2SO_4$) are more effective.
$4$. Option $A$ is incorrect because $MgCl_2$ (providing $Mg^{2+}$) is more effective for the negatively charged gold sol,but the statement implies a comparison that is not standard. However,option $C$ is definitely incorrect because mixing oppositely charged sols leads to mutual coagulation. Thus,the statement 'Mixing the sols has no effect' is false.

(D) The $Hardy-Schulze$ rule states that the greater the valence of the flocculating ion added,the greater is its power to cause precipitation. The coagulating power of an effective ion carrying a charge opposite to that of the sol particles is governed by this rule.

(A) Ferric hydroxide sol $(Fe(OH)_3)$ is a positively charged sol.
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 opposite to that of the colloidal particle.
Since the sol is positively charged,the coagulating power depends on the negative ion (anion).
The valency of the anions in the given options are:
$A$: $[Fe(CN)_6]^{4-}$ (valency = $4$)
$B$: $C_2O_4^{2-}$ (valency = $2$)
$C$: $[Fe(CN)_6]^{3-}$ (valency = $3$)
$D$: $F^-$ (valency = $1$)
Since the anion with the highest valency $(4)$ has the highest coagulating power,$K_4[Fe(CN)_6]$ is the most effective.

(C) Since the two sols are oppositely charged,they undergo mutual coagulation upon mixing due to neutralization of charges. Therefore,the statement that 'mixing the two sols has no effect' is incorrect.

(D) Gelatin is a lyophilic colloid that acts as a protective colloid for lyophobic sols.
Lyophobic sols like $Gold$ sol,$As_2S_3$ sol,and $Fe(OH)_3$ sol are unstable and can be protected by adding lyophilic colloids like gelatin.
Therefore,gelatin acts as a protective colloid for all the given sols.

(B) An emulsion is a type of colloidal system in which both the dispersed phase and the dispersion medium are liquids.
Therefore,it is a colloidal solution of two liquids.

(C) The size of colloidal particles generally ranges from $1 \,nm$ to $1000 \,nm$ ($10^{-9} \,m$ to $10^{-6} \,m$).
In terms of centimeters,this range is $10^{-7} \,cm$ to $10^{-5} \,cm$.

(C) colloidal system is a heterogeneous mixture consisting of two phases:
$1$. The dispersed phase (the substance distributed as colloidal particles).
$2$. The dispersion medium (the medium in which the particles are distributed).
Therefore,a colloidal system consists of both the dispersed phase and the dispersion medium.

(C) The $Pt$ sol is a negatively charged sol. According to the Hardy-Schulze rule,the coagulating power of an electrolyte increases with the increase in the valency of the coagulating ion (the ion carrying a charge opposite to that of the colloidal particles).
For a negatively charged sol,the coagulating power of cations follows the order: $Al^{3+} > Mg^{2+} > Na^+$.
Among the given options,$AlCl_3$ provides $Al^{3+}$ ions,which have the highest valency and are therefore the most effective for the coagulation of the negatively charged $Pt$ sol.

(B) Colloidal particles are electrically charged. When an electric field is applied to a colloidal solution,the particles move towards the oppositely charged electrode. This phenomenon is known as $Electrophoresis$ or $Cataphoresis$.

(B) The Tyndall effect is the phenomenon in which the particles in a colloid scatter the beams of light that are directed at them. This scattering of light makes the path of the beam visible in the colloidal solution. Therefore,the correct answer is $B$.

(C) In dialysis,the semi-permeable membrane allows the passage of small molecules and ions,but it restricts the passage of colloidal particles. Similarly,in osmosis,the semi-permeable membrane allows the solvent molecules (like water) to pass through but prevents the passage of solute particles (colloidal particles or large molecules). Therefore,in both processes,colloidal particles do not pass through the semi-permeable membrane.

(A) The charge on a colloidal particle is determined by the preferential adsorption of ions from the dispersion medium.
$1$. $[Fe(OH)_3]$ is a positively charged sol due to the adsorption of $Fe^{3+}$ ions.
$2$. $[As_2S_3]$ is a negatively charged sol due to the adsorption of $S^{2-}$ ions.
$3$. $[SnO_2]$ is a negatively charged sol due to the adsorption of $SnO_3^{2-}$ ions.
$4$. $[AgI]$ formed by excess $AgNO_3$ adsorbs $Ag^+$ ions and becomes positively charged,not $I^-$.
Therefore,the correctly matched pair is $[Fe(OH)_3] : Fe^{3+}$.

(D) Lyophilic sols are solvent-loving colloids formed by substances like starch,gum,and gelatin which have a high affinity for the dispersion medium.
Metal sulfides are lyophobic colloids,meaning they have little or no affinity for the dispersion medium and require special methods for preparation.
Therefore,metal sulfide is not a lyophilic sol.

(D) Coagulation is the process of aggregating colloidal particles to form a precipitate.
$A$,$B$,and $C$ are examples of coagulation.
Peptization is the process of converting a freshly prepared precipitate into a colloidal sol by adding a small amount of an electrolyte,which is the opposite of coagulation.

(A) colloidal solution is a heterogeneous system in which one substance is dispersed (dispersed phase) as very fine particles in another substance called the dispersion medium.
Therefore,it consists of $2$ phases: the dispersed phase and the dispersion medium.

(B) Milk is a colloidal system in which a liquid is dispersed in another liquid.
Specifically,it consists of fat globules dispersed in water.
Such a colloidal system is known as an $Emulsion$.

(A) Soap lather 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 $Liquid$.