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

(A) true solution is a homogeneous mixture of two or more substances where the solute particles are smaller than $1 \ nm$ in diameter.
$I :$ Urea solution is a true solution.
$II :$ Gelatin is a colloid.
$III :$ Glucose solution is a true solution.
$IV :$ $NaCl$ solution is a true solution.
$V :$ Butter is a colloid (emulsion).
$VI :$ Blood is a colloid.
Therefore,the true solutions are $I, III,$ and $IV$.

(D) The diameter of a particle in a true solution is typically $1 \ \mathring{A}$ to $10 \ \mathring{A}$,while the diameter of a colloidal particle ranges from $10 \ \mathring{A}$ to $1000 \ \mathring{A}$.
Taking the lower limit of the diameter for both,let $d_s = 1 \ \mathring{A}$ and $d_c = 10 \ \mathring{A}$.
The ratio of volumes is given by the ratio of the cubes of their radii (or diameters):
$V_c/V_s = (d_c/d_s)^3 = (10/1)^3 = 10^3$.

(C) Alum contains $Al^{3+}$ ions which neutralize the charge on negatively charged colloidal clay particles,leading to their coagulation and subsequent removal from water.

(D) The $ \text{Gold Number} $ is defined as the minimum weight of a protective colloid in milligrams which must be added to $ 10 \text{ mL} $ of a standard red gold sol so that no coagulation of the gold sol takes place when $ 1 \text{ mL} $ of $ 10\% \text{ NaCl} $ solution is added to it.
Lower $ \text{Gold Number} $ indicates higher protective power.
Among the given options,$ \text{Gelatin} $ has the lowest $ \text{Gold Number} $ $( 0.005-0.01 )$,while $ \text{Potato starch} $ has the highest $ \text{Gold Number} $ $( 25 )$.

(A) The Critical Micelle Concentration $(CMC)$ decreases as the length of the hydrophobic hydrocarbon chain increases.
Comparing the given surfactants,the chain length in option $A$ is $16$ carbons,which is the longest among the choices.
Longer hydrocarbon chains increase the hydrophobic effect,leading to micelle formation at a significantly lower concentration compared to shorter chains.

(B) cationic micelle is formed by surfactants that have a positively charged head group in an aqueous solution.
$Cetyltrimethylammonium \ bromide$ $(CH_3(CH_2)_{15}N(CH_3)_3^+Br^-)$ dissociates in water to give a long-chain cation $(CH_3(CH_2)_{15}N(CH_3)_3^+)$,which forms cationic micelles.
$Sodium \ dodecyl \ sulphate$ and $Sodium \ stearate$ form anionic micelles because they contain negatively charged head groups ($SO_4^-$ and $COO^-$ respectively).
$Urea$ is a non-ionic solute and does not form micelles.

(B) liquid that scatters a beam of light exhibits the $Tyndall$ effect,which is a characteristic property of colloidal solutions (sols).
Since it passes through filter paper without leaving any residue,it cannot be a suspension (which would leave a residue).
Therefore,the substance is a $Sol$.

(C) Peptization is the process of converting a freshly prepared precipitate into a colloidal sol by adding a small amount of an electrolyte,known as a peptizing agent.
Therefore,the correct statement is that the precipitate is converted into a colloid.

(C) Dialysis is a process used to separate colloidal particles from crystalloids based on their ability to pass through a semi-permeable membrane.
Colloidal particles (like proteins) cannot pass through the membrane,whereas crystalloids (like glucose) can pass through it.
Therefore,a mixture of glucose (crystalloid) and protein (colloid) can be separated by dialysis.

(A) Electrophoresis is the movement of colloidal particles under an applied electric field.
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.
If the particles accumulate near the negative electrode,they are positively charged,and if they accumulate near the positive electrode,they are negatively charged.
The movement of colloidal particles under an applied electric field is called electrophoresis.

(C) When an electric field is applied to a colloidal system,if the movement of dispersed particles is prevented by some suitable means (like a semi-permeable membrane),the dispersion medium begins to move under the influence of the electric field. This phenomenon is known as $Electro-osmosis$.

(B) Light scattering by colloidal particles is known as the $Tyndall \ effect$.
Colloidal particles are large enough to scatter light,whereas particles in a true solution are too small to scatter light.
Therefore,light scattering is observed in a colloidal solution.

(D) Colloidal sols are classified based on the charge of the dispersed phase particles.
$1$. Gold sol and Arsenic sulphide $(As_2S_3)$ sol are examples of negatively charged sols.
$2$. Starch is a lyophilic colloid which is generally neutral or weakly charged.
$3$. Ferric hydroxide $(Fe(OH)_3)$ sol is a well-known example of a positively charged sol.
Therefore,the correct option is $D$.

(D) An insecticide spray is an example of an aerosol where a liquid is dispersed in a gas.
Therefore,the dispersed phase is $Liquid$ and the dispersion medium is $Gas$.

(B) Micelles are associated colloids formed by the aggregation of a large number of ions in concentrated solutions.
Since the number of particles decreases significantly due to the formation of aggregates (micelles),the colligative properties (such as osmotic pressure,freezing point depression,etc.) of micellar solutions are lower than those of individual ions in a normal colloidal sol.

(A) The given reaction is $SO_{2(g)} + 2H_2S_{(g)} \rightarrow 3S_{(sol)} + 2H_2O_{(l)}$.
In this reaction,$SO_2$ reacts with $H_2S$ to produce colloidal sulfur (sol).
This process involves the reaction of two compounds where the positive and negative ions are exchanged or rearranged to form a new product,which is characteristic of a double decomposition reaction.
Therefore,the correct method is double decomposition.

(B) Micelles are formed by surfactants or surface-active agents that contain both a hydrophobic tail and a hydrophilic head.
$Cetyltrimethylammonium \ bromide$ $(CTAB)$,$Sodium \ dodecyl \ sulphate$ $(SDS)$,and $Sodium \ stearate$ are all surfactants that form micelles in aqueous solution.
However,in the context of standard chemistry curriculum questions of this type,$Cetyltrimethylammonium \ bromide$ is a classic example of a cationic surfactant,while $Sodium \ dodecyl \ sulphate$ and $Sodium \ stearate$ are anionic surfactants.
Since the question asks which of the following can form micelles,all options except $Urea$ are correct.
If this is a single-choice question,$Cetyltrimethylammonium \ bromide$ is often cited as a primary example of a cationic micelle-forming agent.

(D) $Fe(OH)_3$ sol is prepared by the hydrolysis of $FeCl_3$ in hot water.
It is a positively charged sol because of the preferential adsorption of $Fe^{3+}$ ions on the surface of the colloidal particles.
Therefore,it is a positively charged colloid.

(B) Cassius purple is a colloidal dispersion of gold particles in stannic acid. The characteristic purple color is due to the presence of finely divided colloidal gold particles.

(C) Colloidal particles are intermediate between true solutions and suspensions.
The size range of colloidal particles is generally considered to be between $1 \ \text{nm}$ and $1000 \ \text{nm}$.
Since $1 \ \text{nm} = 10 \ \mathring{A}$,the range in $\mathring{A}$ units is $10 \ \mathring{A}$ to $10000 \ \mathring{A}$.
Among the given options,the range $10$ to $1000 \ \mathring{A}$ is the most appropriate representation for colloidal particles.

(B) The process of converting a freshly prepared precipitate into a colloidal sol by adding a small amount of a suitable electrolyte is called $Peptization$.
In this case,$Fe(OH)_3$ precipitate is converted into a ferric hydroxide sol by adding a small amount of $HCl$ (electrolyte) and boiling it.

(C) colloidal solution of arsenious sulphide $(As_2S_3)$ is prepared by the double decomposition method.
The chemical reaction is: $As_2O_3 + 3H_2S \rightarrow As_2S_3 + 3H_2O$.

(A) 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 a negatively charged sol,the coagulating power of the cation increases with its valency.
The valencies of the cations in the given options are:
$Al^{3+}$ $(AlCl_3)$,$K^+$ $(K_2SO_4)$,$Na^+$ $(NaOH)$,and $H^+$ $(HCl)$.
Since $Al^{3+}$ has the highest valency $(+3)$,it has the highest coagulating power.
Therefore,the minimum amount of $AlCl_3$ is required for coagulation.

(B) The chemical oxidation method is used to prepare colloidal sols of non-metals like sulfur.
For example,when hydrogen sulfide $(H_2S)$ gas is passed through an aqueous solution of sulfur dioxide $(SO_2)$,sulfur sol is formed:
$2H_2S(g) + SO_2(aq) \rightarrow 2H_2O(l) + 3S(sol)$
Here,$H_2S$ is oxidized to $S$ by $SO_2$.

(A) Hydrophilic sols are formed by substances like starch,gum,proteins,etc.,which have a strong affinity for the dispersion medium.
These sols are reversible in nature,meaning they can be easily reformed by simply mixing the dispersed phase with the dispersion medium after evaporation or coagulation.

(B) Micelles are formed by the aggregation of a large number of ions or molecules in a concentrated solution. These are known as associated colloids. Therefore,a micelle is an associated colloid.

(A) The movement of colloidal particles under the influence of an 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.

(B) The $Hardy-Schulze$ rule states that:
$1$. The ions carrying charge opposite to that of the sol particles are effective in causing coagulation.
$2$. The greater the valence of the coagulating ion (or flocculating ion),the greater is its power to cause coagulation.
For example,for a negatively charged sol,the coagulating power of cations follows the order: $Al^{3+} > Ba^{2+} > Na^+$.
Therefore,option $B$ is the correct statement.

(C) The classification of colloids is based on the dispersed phase and dispersion medium:
$I$. Smoke is a solid dispersed in a gas,which is an aerosol $(I-B)$.
$II$. Gelatin is a solid dispersed in a liquid,which is a sol $(II-A)$.
$III$. Soap lather is a gas dispersed in a liquid,which is a foam $(III-D)$.
$IV$. Milk is a liquid dispersed in a liquid,which is an emulsion $(IV-C)$.
Therefore,the correct matching is $I-B, II-A, III-D, IV-C$.

(B) surfactant is a molecule that has both a hydrophobic (long hydrocarbon chain) and a hydrophilic (polar or ionic head) part.
$C_{17}H_{35}COO^{-}Na^{+}$ is sodium stearate,which is a classic example of a soap (surfactant).
It consists of a long non-polar hydrophobic tail $(C_{17}H_{35}-)$ and a polar hydrophilic head $(-COO^{-}Na^{+})$.

(D) $sol$ is a type of colloidal system where solid particles are dispersed in a liquid medium. Properties such as $Adsorption$,$Tyndall \text{ effect}$,and $Coagulation$ are characteristic properties of colloidal systems (sols). $Paramagnetism$ is a magnetic property of substances related to the presence of unpaired electrons,which is not a characteristic property of a $sol$.

(B) The protective power of a lyophilic colloid is inversely proportional to its gold number.
Gold number is defined as the minimum amount of protective colloid in milligrams that prevents the coagulation of $10 \ mL$ of a standard gold sol when $1 \ mL$ of $10\% \ NaCl$ solution is added to it.
Given gold numbers:
$A = 0.04$
$B = 0.002$
$C = 10$
$D = 25$
Since protective power $\propto \frac{1}{\text{Gold number}}$,the smaller the gold number,the higher the protective power.
Comparing the values: $0.002 < 0.04 < 10 < 25$.
Therefore,the order of protective power is $B > A > C > D$.

(A) 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 sol.
Since $As_2S_3$ sol is negatively charged,it requires a positively charged ion for coagulation.
The coagulating power follows the order: $Al^{3+} > Ca^{2+} > Na^+$.
Therefore,$AlCl_3$ is the most effective coagulating agent among the given options because it provides $Al^{3+}$ ions.

(B) The stability of lyophilic colloids is primarily due to two factors: the charge on the particles and the solvation of the particles.
Specifically,the particles are heavily solvated,meaning they are surrounded by a layer of the dispersion medium,which prevents them from coming close enough to aggregate.

(C) 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 and detergents are classic examples of associated colloids because their molecules contain both a lyophilic and a lyophobic part,which aggregate to form micelles above the Critical Micelle Concentration $(CMC)$.

(D) Albumin is a protein that forms a lyophilic sol when mixed with water.
Lyophilic colloids are reversible in nature,meaning they can be reformed by simply adding the dispersion medium after evaporation.
They also act as protective colloids because they prevent the coagulation of lyophobic colloids.
Therefore,all the given statements are correct.

(A) In milk,the dispersed phase consists of fat globules in a liquid state,while the dispersion medium is water,which is also in a liquid state. Therefore,it is a liquid-in-liquid colloidal system.

(B) Lyophobic colloids are solvent-hating colloids that are not easily prepared by direct mixing.
$Gelatin$,$Starch$,and $Agar-agar$ are examples of lyophilic (solvent-loving) colloids.
$Phosphorus$ sol is a classic example of a lyophobic colloid.

(B) Gelatin is used as a protective colloid in the preparation of ice cream. It acts as a stabilizer that prevents the formation of large ice crystals,thereby maintaining the smooth,creamy colloidal texture of the ice cream.

(A) The Tyndall effect is the phenomenon in which colloidal particles scatter light when a beam of light is passed through a colloidal solution. This scattering makes the path of the light beam visible in the colloidal dispersion. Therefore,colloidal particles show intense scattering of light in the Tyndall effect.

(A) The colloidal properties,specifically the molar mass of polymers in a colloidal solution,are determined by the method of $Light \ Scattering$.
This technique measures the intensity of light scattered by the polymer molecules in the solution,which is proportional to the molar mass of the polymer.
Therefore,the correct method is light scattering.

(D) Dialysis is a process used to separate particles of colloidal dimensions from those of smaller dimensions (crystalloids) in a mixture.
Colloidal particles (like proteins) cannot pass through a semi-permeable membrane,whereas crystalloids (like glucose,salts) can pass through it.
Among the given options,glucose is a crystalloid and protein is a colloid.
Therefore,dialysis can be used to separate glucose and protein.

(A) The purple of Cassius is a purple-colored pigment formed by the reaction of gold salts with tin$(II)$ chloride.
It consists of colloidal gold particles adsorbed on tin$(IV)$ oxide (stannic acid) particles.
Therefore,the purple color is due to the presence of colloidal gold.

(C) Sodium stearate is a soap with the formula $CH_3(CH_2)_{16}COO^{-}Na^{+}$.
It consists of a long non-polar hydrocarbon tail $(CH_3(CH_2)_{16}-)$ and a polar head $(-COO^{-}Na^{+})$.
The polar head part is the carboxylate group,represented as $-COO^{-}$.

(A) Detergents are surfactants,which means they are surface-active agents. $
ewline $ When added to water,they accumulate at the interface between water and air or water and oil. $
ewline $ This accumulation disrupts the cohesive forces between water molecules,thereby significantly reducing the surface tension of water. $
ewline $ This property allows water to wet surfaces more effectively and helps in the cleaning process.

(B) The gold number is defined as the minimum amount of a protective colloid in $mg$ that is required to prevent the coagulation of $10 \, mL$ of a standard gold sol when $1 \, mL$ of $10 \% \ NaCl$ solution is added to it.
Given that $0.25 \, g$ of substance '$X$' prevents coagulation in $100 \, mL$ of gold sol.
Convert the mass of '$X$' to $mg$: $0.25 \, g = 0.25 \times 1000 \, mg = 250 \, mg$.
Since $250 \, mg$ of '$X$' is required for $100 \, mL$ of gold sol,the amount required for $10 \, mL$ of gold sol is:
$\frac{250 \, mg}{100 \, mL} \times 10 \, mL = 25 \, mg$.
Therefore,the gold number of '$X$' is $25$.

(C) The correct answer is $(C)$.
Hydrophilic sols (lyophilic colloids) have a strong affinity between the dispersed phase and the dispersion medium.
Due to this interaction,the viscosity of these sols is significantly higher than that of the dispersion medium (water),and their surface tension is generally lower than that of water.
Therefore,the statement that viscosity and surface tension are about the same as for water is incorrect.

(A) The process of converting a freshly prepared precipitate into colloidal particles by adding a suitable electrolyte is called peptisation. The electrolyte added for this purpose is known as a peptising agent.