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

(D) Absorption,Tyndall effect,and flocculation are all properties or phenomena associated with sols. Paramagnetism is a magnetic property of substances and is not a characteristic property of sols.

(A) Intrinsic colloids are also known as lyophilic colloids.
These substances directly form colloidal solutions when mixed with a dispersion medium.
Glue,starch,and proteins are examples of intrinsic colloids.
Therefore,the correct option is $(A)$.

(C) The colloidal solution of arsenious sulphide $(As_2S_3)$ is prepared by the double decomposition method.
In this process,a dilute solution of arsenious oxide $(As_2O_3)$ is passed through a solution of hydrogen sulphide $(H_2S)$:
$As_2O_3 + 3H_2S \to As_2S_3 + 3H_2O$

(C) According to the $Hardy-Schulze$ rule,the coagulating power of an electrolyte depends on the valency of the active ion (flocculating ion).
Greater the valency of the flocculating ion,the greater is its power to cause coagulation of the sol.

(C) The gold number is defined as the minimum mass of a 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.
It is a measure of the protective power of a lyophilic colloid.
Therefore,the correct option is $C$.

(C) The correct answer is $(C)$.
$A$ colloidal solution of a liquid dispersed in another liquid is known as an emulsion,not a gel.
$A$ gel is a colloidal system where a liquid is dispersed in a solid.

(C) Gum-arabic acts as a protective colloid. In the preparation of Indian ink,it prevents the coagulation of carbon particles (lamp black) by forming a protective layer around them,thereby stabilizing the colloidal suspension. Thus,its function is $Protective \ action$.

(B) Cationic micelles are formed by surfactants where the long-chain cation is the active part.
$Cetyltrimethylammonium \ bromide$ $(CH_3(CH_2)_{15}N(CH_3)_3^+Br^-)$ dissociates in water to give a long-chain cation,which aggregates to form cationic micelles.
$Sodium \ dodecyl \ sulphate$ and $Sodium \ acetate$ form anionic micelles because the long-chain part is an anion.
$Urea$ does not form micelles.

(A) The 'Purple of Cassius' is a colloidal solution of gold.
It is prepared by the reduction of auric chloride $(AuCl_3)$ with stannous chloride $(SnCl_2)$.
Therefore,the correct option is $A$.

(B) An amphiphile is a chemical compound possessing both hydrophilic (water-loving) and lipophilic (fat-loving) properties.
Such a compound is called amphiphilic or amphipathic.
This property is the basis for the cleaning action of soaps and detergents,where the hydrophobic tail interacts with grease and the hydrophilic head interacts with water.
Therefore,amphiphilic molecules are normally associated with soaps and detergents.

(C) The process of precipitation of soap from its colloidal solution is known as 'salting out'.
$NaCl$ is commonly used for this purpose because the common ion effect of $Na^+$ ions decreases the solubility of soap (sodium salt of fatty acids).
Any other soluble sodium salt that provides $Na^+$ ions can also be used for this purpose.
Among the given options,$Na_2SO_4$ is a soluble salt that provides $Na^+$ ions and can effectively precipitate soap.

(D) Dialysis is a process used to separate particles of different sizes using a semipermeable membrane.
Small molecules like $Glucose$ can easily pass through the pores of the semipermeable membrane.
However,large molecules like $Proteins$ (colloidal particles) cannot pass through the semipermeable membrane.
Therefore,dialysis is effective in separating $Glucose$ and $Proteins$.

(A) During the production of cement,gypsum $(CaSO_4 \cdot 2H_2O)$ is added to the clinker to retard the setting time of cement,allowing it to be worked with for a longer period before it hardens.

(B) The correct answer is $Silver \ bromide$ $(AgBr)$.
$AgBr$ is highly light-sensitive and undergoes a photochemical reduction reaction when exposed to light.
The chemical reaction is: $2AgBr \xrightarrow{h\nu} 2Ag + Br_2$.

(B) Colligative properties depend on the number of particles in the solution.
Colloidal particles are aggregates of many molecules,which results in a smaller number of particles compared to a true solution of the same concentration.
Therefore,the magnitude of the colligative property of a colloidal solution is lower than that of a true solution.

(B) Colloidal solutions are classified into two types based on the interaction between the dispersed phase and the dispersion medium: $1.$ Lyophilic (solvent-loving) and $2.$ Lyophobic (solvent-hating).
When water is the dispersion medium,these are called hydrophilic and hydrophobic colloids,respectively.
Metal hydroxides like $Fe(OH)_3$ and metal sulfides are typical examples of lyophobic colloids.
Since $Fe(OH)_3$ does not have a strong affinity for water,it forms a hydrophobic colloid.

(B) The concept of $Gold \ Number$ was introduced by the scientist $Richard \ Adolf \ Zsigmondy$ in $1901$.
It is defined as the minimum amount of protective colloid in milligrams which prevents the coagulation of $10 \ mL$ of a gold sol when $1 \ mL$ of $10\% \ NaCl$ solution is added to it.

(C) The continuous zigzag motion of colloidal particles in a dispersion medium is called $Brownian$ $movement$.
$Electrophoresis$ is the movement of colloidal particles under an applied electric field.
$Tyndall$ $effect$ is the scattering of light by colloidal particles.
$Electro-osmosis$ is the movement of the dispersion medium under an electric field when the movement of colloidal particles is prevented.

(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.
Greater the valency of the flocculating ion added,the greater is its power to cause precipitation.
The order of coagulating power for the given ions is: $Na^{+} < Sr^{2+} < Pb^{2+} < Pb^{4+}$.
Therefore,$Na^{+}$ has the minimum coagulating power.

(D) The gold number is defined as the minimum amount of a 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 that $1000 \ mg$ of the colloid protects $100 \ mL$ of the sol.
To find the amount for $10 \ mL$ of the sol,we use the ratio:
$\text{Gold number} = \frac{1000 \ mg}{100 \ mL} \times 10 \ mL = 100 \ mg$.
Since $100 \ mg$ is not among the given options,the correct answer is $None$.

(B) colloid is a mixture where one substance of microscopically dispersed insoluble particles is suspended throughout another substance.
Blood is a natural colloid because it consists of various components like proteins (e.g.,albumin,globulin) and cells suspended in plasma.
$NaCl$ and sugar form true solutions,while $RCOONa$ (soap) forms micelles in water,which are associated colloids.

(C) Brownian motion is the continuous,random,zig-zag motion of colloidal particles in a dispersion medium.
It is caused by the unbalanced bombardment of the particles of the dispersion medium on the colloidal particles.

(B) Colloidal particles are intermediate in size between true solutions and suspensions.
The range of diameter for colloidal particles is typically considered to be between $1 \, nm$ and $1000 \, nm$ (which is equivalent to $10^{-9} \, m$ to $10^{-6} \, m$).
In terms of micrometers,$1000 \, nm$ is equal to $1 \, \mu m$.
Therefore,the range is $1 \, nm$ to $1000 \, nm$ or $10^{-9} \, m$ to $10^{-6} \, m$.

(B) The potential difference between the fixed layer and the diffused layer of opposite charges is known as the $Zeta \text{ } potential$ or $electrokinetic \text{ } potential$.

(C) Colloidal particles are intermediate in size between true solutions and suspensions.
Their diameter typically ranges from $1 \ \text{nm}$ to $1000 \ \text{nm}$.
Since $1 \ \text{nm} = 10 \ \overset{o}{A}$,the range in $\mathring{A}$ units is $10 \ \overset{o}{A}$ to $10000 \ \overset{o}{A}$.
Among the given options,the range $10$ to $1000 \ \overset{o}{A}$ is the most appropriate representation for colloidal particles.

(D) Colloidal sols are thermodynamically unstable systems because they have a high surface energy due to the large surface area of the dispersed phase particles. They are kinetically stable due to the presence of charge or solvation,but they tend to coagulate or settle over time. Therefore,the statement that colloidal sols are thermodynamically stable is incorrect.

(A) Blood is a colloidal solution of albuminoid substances.
It contains various impurities and electrolytes.
Dialysis is the process of separating particles of colloids from those of crystalloids by means of diffusion through a suitable membrane.
Since blood is a colloid,it is purified by the process of dialysis.

(A) Hydrophilic sols are liquid-loving colloids where the dispersed phase has a strong affinity for the dispersion medium (water).
Starch,proteins,and gums are common examples of hydrophilic colloids.
Silver iodide and arsenic sulfide are examples of hydrophobic sols.

(C) system where a solid (cellulose) is dispersed in a liquid (alcohol) is a type of colloidal system known as a sol. Since the dispersion medium is alcohol (an organic solvent),it is specifically referred to as an organosol. Among the given options,'Colloid' is the most appropriate classification for this system.

(D) The Tyndall effect is a phenomenon where light is scattered by particles in a colloid or a fine suspension.
$NaCl$ solution is a true solution,where the solute particles are very small (less than $1 \ nm$ in diameter).
In a true solution,the particles are too small to scatter light,so the Tyndall effect is not observed.
Suspensions,starch sols,and gold sols are either colloids or suspensions,which contain larger particles capable of scattering light.

(B) Multimolecular colloids are formed by the aggregation of a large number of atoms or smaller molecules with a diameter of less than $1 \ nm$. These particles are held together by weak $Van \ der \ Waals$ forces of attraction. Examples include gold sol and sulfur sol.

(D) According to the $Hardy-Schulze$ law,the coagulating power of an ion depends on the valency (magnitude of charge) of the active ion.
Greater the valency of the flocculating ion added,the greater is its power to cause precipitation.
Additionally,the ion must have a charge 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) The $Tyndall$ effect is the primary and most common optical phenomenon used to distinguish between a true solution and a colloidal solution. When a beam of light is passed through a colloidal solution,the particles scatter the light,making the path of the beam visible. This does not happen in a true solution because the particles are too small to scatter light.

(A) Brownian motion is the continuous,random,and zig-zag motion of colloidal particles suspended in a medium. This motion is caused by the collision of molecules of the dispersion medium with the colloidal particles. Since it involves the movement of particles over time,it is considered a kinetic phenomenon. The Tyndall effect,on the other hand,is an optical phenomenon related to the scattering of light by colloidal particles.

(B) Thomas Graham classified substances into two categories based on their ability to diffuse through a parchment paper or animal membrane.
Substances that can pass through these membranes are known as $Crystalloids$.
Substances that cannot pass through these membranes are known as $Colloids$.

(C) The $Sb_2S_3$ 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 with a charge opposite to that of the sol).
Since $Sb_2S_3$ is negatively charged,the positive ions are responsible for coagulation.
The valencies of the positive ions are:
$Na^+$ $(+1)$,$Ca^{2+}$ $(+2)$,$Al^{3+}$ $(+3)$,and $NH_4^+$ $(+1)$.
Since $Al^{3+}$ has the highest valency $(+3)$,$Al_2(SO_4)_3$ is the most effective coagulating agent.

(D) According to the Hardy-Schulze rule,the coagulating power of an ion is directly proportional to its valency.
Greater the valency of the flocculating ion,the greater is its coagulating power.
Coagulating power is inversely proportional to the coagulation value.
Therefore,the ion with the highest valency will have the minimum coagulation value.
Comparing the valencies: $Cl^{-}$ $(1)$,$SO_4^{2-}$ $(2)$,$PO_4^{3-}$ $(3)$,$[Fe(CN)_6]^{4-}$ $(4)$.
The ion $[Fe(CN)_6]^{4-}$ has the highest valency of $4$,hence it has the minimum coagulation value.

(C) The Tyndall effect is observed in colloidal systems where particles are large enough to scatter light.
$A$ sugar solution is a true solution,where the particle size is very small (less than $1 \ nm$),so it does not scatter light and thus does not show the Tyndall effect.

(B) Arsenious sulphide $(As_2S_3)$ sol is a negatively charged colloid.
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 particles.
Since the sol is negative,it is coagulated by positive ions.
The coagulating power increases with the increase in the magnitude of the charge on the cation.
Therefore,the order is $Al^{3+} > Ba^{2+} > Na^{+}$.

(A) soap film has two surfaces,so the change in area is doubled.
Initial area $A_1 = 5 \, cm \times 5 \, cm = 25 \, cm^2 = 25 \times 10^{-4} \, m^2$.
Final area $A_2 = 10 \, cm \times 10 \, cm = 100 \, cm^2 = 100 \times 10^{-4} \, m^2$.
Change in area $\Delta A = A_2 - A_1 = (100 - 25) \times 10^{-4} \, m^2 = 75 \times 10^{-4} \, m^2$.
Work done $W = 2 \times S \times \Delta A$,where $S$ is surface tension.
$W = 2 \times (30 \times 10^{-3} \, N/m) \times (75 \times 10^{-4} \, m^2) = 4500 \times 10^{-7} \, J = 4.5 \times 10^{-4} \, J$.

(B) Coagulation is the process of aggregating colloidal particles to form a precipitate.
$A$,$C$,and $D$ are examples of coagulation processes.
Peptization is the reverse process,where a freshly prepared precipitate is converted into a colloidal sol by adding a suitable electrolyte.

(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,it is the dispersion of a precipitate into a colloidal sol.

(A) Lyophilic colloids are solvent-attracting colloids. They are formed by mixing substances like gums,gelatin,starch,or proteins directly with the dispersion medium.
$A$. Gelatin is a protein and acts as a lyophilic colloid.
$B, C, D$. Sulfur,Gold,and Carbon form lyophobic colloids when dispersed in water.

(B) Lyophilic colloids are solvent-loving colloids. They are stable and reversible in nature,meaning they can be easily reformed after coagulation by simply adding the dispersion medium. Irreversibility is a characteristic property of lyophobic colloids,not lyophilic colloids.

(B) In the given reaction,$AuCl_3$ is reduced to $Au$ (sol) by formaldehyde $(HCHO)$.
The oxidation state of $Au$ changes from $+3$ in $AuCl_3$ to $0$ in $Au$ (sol).
Since the oxidation state decreases,this is a reduction reaction.

(D) An emulsifier is a substance that stabilizes an emulsion by increasing its kinetic stability.
$Gum$,$Agar$,and $Soap$ act as emulsifying agents.
$Milk$ is an emulsion itself (fat dispersed in water),not an emulsifier.

(A) Bredig's arc method is used for the preparation of colloidal sols of noble metals like $Au$,$Ag$,and $Pt$.
In this method,an electric arc is struck between electrodes of the metal immersed in a dispersion medium.
$K$ (Potassium) is a highly reactive alkali metal that reacts violently with water (the dispersion medium),making it impossible to prepare a stable sol using this method.

(B) According to the $Hardy-Schulze$ rule,the coagulating power of an ion is directly proportional to its valency for the coagulation of a sol.
For a negatively charged sol like arsenic sulphide $(As_2S_3)$,the coagulating power of cations increases with the increase in their positive charge.
The valencies of the given ions are: $Na^{+} (+1)$,$Ba^{2+} (+2)$,and $Al^{3+} (+3)$.
Therefore,the increasing order of coagulating power is $Na^{+} < Ba^{2+} < Al^{3+}$.

(A) An emulsifier is a substance that stabilizes an emulsion by increasing its kinetic stability.
Soap acts as an emulsifier because it contains both a hydrophilic head and a hydrophobic tail,which allows it to bridge the interface between oil and water,preventing the droplets from coalescing.
Therefore,soap is the correct answer.