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

(D) $Blood$ is a natural colloid.
$Sodium$ $chloride$,cane sugar,and urea dissolve completely in water to form a homogeneous solution,whereas $Blood$ consists of particles in the colloidal range dispersed in a liquid medium.

(D) Sodium stearate $(C_{17}H_{35}COONa)$ is the sodium salt of stearic acid and acts as a soap.
When dissolved in water,it forms micelles due to the aggregation of its long hydrocarbon chains and polar carboxylate heads.
These micelles have a size range of $1 \ nm$ to $1000 \ nm$,which is characteristic of a colloidal solution.
Therefore,sodium stearate forms a colloidal solution in water.

(D) Blood is a colloidal system. It contains negatively charged particles (like blood corpuscles) and positively charged particles (like hemoglobin).

(C) Brownian motion is the continuous zig-zag movement of colloidal particles. It is caused by the unbalanced bombardment of the particles of the dispersed phase by the molecules of the dispersion medium.

(A) Colloidal particles are too small to be seen directly under an ordinary microscope because their size is smaller than the wavelength of visible light.
However,when a colloidal solution is observed under an ultramicroscope,the light scattered by the colloidal particles makes them visible as bright spots against a dark background.
Therefore,we can see the light scattered by the colloidal particles.

(C) The properties of a colloidal solution depend on the physical state of the dispersed phase and its molecular weight. Therefore,the correct option is $C$.

(D) According to the $Hardy-Schulze$ rule,the flocculating 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.
Comparing the charges: $Pb^{4+} > Pb^{2+} = Sr^{2+} > Na^{+}$.
Therefore,the ion with the minimum charge has the minimum flocculating power.
Among the given options,$Na^{+}$ has the minimum charge $(+1)$,so it has the minimum flocculating power.

(D) According to Graham,colloids are defined as substances that can be separated from crystalloids by diffusion through a parchment paper or animal membrane.

(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 effect is exhibited by all colloidal solutions due to the size of the colloidal particles being comparable to the wavelength of light.

(B) liquid aerosol is a type of colloid where a liquid is the dispersed phase and a gas is the dispersion medium.
Examples include cloud,fog,and mist.

(C) colloid is a mixture where one substance is dispersed in another dispersion medium without chemical reaction.
Butter is an example of an emulsion,which is a type of colloid where a liquid is dispersed in another liquid.
Specifically,butter is formed when water is dispersed in fat.

(D) colloidal solution is a heterogeneous system in which one substance is dispersed as very fine particles in another substance called the dispersion medium.
Colloids can be formed by substances that are insoluble in each other.
They can be formed by substances in the same physical state (e.g.,emulsions like milk,where liquid is dispersed in liquid) or in different physical states (e.g.,sols,aerosols).
Since colloids can be formed in all these conditions,none of the given options correctly describe a condition where a colloid cannot be obtained.

(B) The reaction $2HNO_3 + 3H_2S \to 3S + 4H_2O + 2NO$ leads to the formation of sulfur $(S)$ in the colloidal state.
In the presence of excess $HCl$,the sulfur particles formed by the oxidation of $H_2S$ aggregate to form a colloidal sol.

(B) Lyophobic colloids are irreversible in nature. Once they are precipitated,they cannot be easily converted back into the colloidal state by simple addition of the dispersion medium.

(B) Substances are classified into two categories based on their ability to diffuse through semi-permeable or parchment membranes:
$1$. $Crystalloids$: These are substances whose particles are small enough to pass through parchment membranes.
$2$. $Colloids$: These are substances whose particles are larger and cannot pass through parchment membranes.
Therefore,the correct answer is $(b)$ $Crystalloids$.

(A) The size of colloidal particles is intermediate between true solutions and suspensions.
The range of particle size for colloids is typically $1 \ nm$ to $1000 \ nm$.
Converting this to meters: $1 \ nm = 10^{-9} \ m$ and $1000 \ nm = 10^{-6} \ m$.
Among the given options,the range $10^{-9} \ m$ to $10^{-7} \ m$ (which is $1 \ nm$ to $100 \ nm$) represents the standard colloidal range.
Therefore,the correct option is $A$.

(B) Jelly is a colloidal solution of sweetened fruit,water,and a thickener called pectin.
In this system,the dispersed phase is a liquid (water or sugar syrup) and the dispersing medium is a solid (bits of sweetened fruit pulp).
It belongs to the category of '$gel$' type of colloid.

(C) Blood is a colloidal system where blood cells and proteins act as negatively charged $(-ve)$ sol particles. When ferric chloride $(FeCl_3)$ is applied,the $Fe^{3+}$ ions neutralize the charge on these particles,causing coagulation. This coagulated mass seals the blood vessel,thereby stopping the bleeding.

(C) Colloidal particles have a size range of $1 \ nm$ to $1000 \ nm$.
Filter paper has relatively large pores,which allow colloidal particles to pass through easily.
However,animal or vegetable membranes (like parchment paper or cellophane) have very fine pores that are smaller than the size of colloidal particles,preventing them from passing through.
Therefore,colloidal particles can pass through filter paper but not through animal membranes.

(B) Casein is the emulsifying agent in milk,which stabilizes the emulsion by keeping the two immiscible phases,fat and water,together.

(B) Butter is a type of colloid known as an emulsion. Specifically,it is a water-in-oil $(W/O)$ type emulsion where water droplets are dispersed in a continuous phase of fat.

(B) An emulsion is a type of colloid where both the dispersed phase and the dispersion medium are liquids.
Therefore,it is a colloidal dispersion of a liquid in a liquid.

(D) colloidal solution of certain elements such as mercury and sulphur is obtained by passing their vapors through cold water containing a stabilizer (an ammonium salt or citrate). This process is known as ultrasonic dispersion or by using specialized dispersion techniques for metals like mercury.

(C) Dialysis is a process of separating the particles of colloids from those of crystalloids by means of diffusion through a suitable membrane.
The rate of diffusion is directly proportional to the temperature of the solution.
Additionally,the nature of the colloidal substance and the membrane also influences the process.
Therefore,the rate of dialysis depends upon both the nature of the colloidal substance and the temperature of the solution.

(C) An emulsifier is a substance that stabilizes an emulsion by reducing the interfacial tension between the two immiscible liquids,thereby increasing its kinetic stability.
In egg yolk,the main emulsifying agent is lecithin. Other common examples of emulsifiers include soy lecithin,sodium phosphates,and sodium stearoyl lactylate.

(B) Lyophilic colloids are solvent-loving,meaning the dispersed phase has a strong affinity for the dispersion medium.
Lyophobic colloids are solvent-hating,meaning the dispersed phase has little to no affinity for the dispersion medium.
Therefore,the fundamental difference between these two types of colloids lies in their interaction or behaviour towards the dispersion medium.

(A) When a substance is converted into a colloidal state,the particle size decreases significantly. Since the total volume remains constant,the reduction in particle size leads to a massive increase in the total surface area of the particles. Therefore,the correct option is $A$.

(B) Electrodialysis is a process used to purify colloidal solutions by removing ionic impurities using an electric field.
$(B)$ Alum is an electrolyte that dissociates into $Al^{3+}$ and $SO_4^{2-}$ ions in an aqueous solution.
Since these ions are electrolytes,they can be separated from the colloidal particles using electrodialysis,whereas substances like alcohol,sugar,and urea are non-electrolytes and cannot be separated by this method.

(D) The stability of a lyophobic sol is primarily attributed to two factors:
$1$. The presence of a similar electric charge on all colloidal particles,which causes electrostatic repulsion and prevents them from aggregating.
$2$. Brownian motion,which keeps the particles in constant random motion,preventing them from settling down due to gravity.

(D) According to the Hardy-Schulze rule,the coagulating power of an electrolyte depends on the valency of the active ion (the ion with a charge opposite to that of the colloidal particles).
$As_2S_3$ is a negatively charged sol,so it requires a positively charged ion for coagulation.
The coagulating power increases with the increase in the valency of the flocculating ion: $Al^{3+} > Ba^{2+} > Na^+$.
Since the coagulation value is inversely proportional to the coagulating power,the electrolyte with the highest valency of the active ion will have the lowest coagulation value.
Therefore,$AlCl_3$ has the lowest coagulation value.

(C) Substances that behave as normal electrolytes at low concentrations but exhibit colloidal behavior at higher concentrations due to the aggregation of particles are called associated colloids. These aggregated particles are known as $Micelles$.

(C) Silver iodide $(AgI)$ is used for producing artificial rain because it has a crystal structure similar to ice.
When $AgI$ is sprayed over clouds,it acts as a nucleating agent,causing water droplets in the clouds to coalesce to form bigger water drops,which then fall as rain.

(D) Gelatin acts as a protective colloid in ice-cream. It prevents the formation of large ice crystals,thereby maintaining the smooth texture of the ice-cream.

(A) An emulsion is a colloidal system in which both the dispersed phase and the dispersion medium are liquids.
In a $water$ in $oil$ $(W/O)$ type emulsion,water is the dispersed phase and oil is the dispersion medium.
Butter is a classic example of a $water$ in $oil$ type emulsion,where water droplets are dispersed in a continuous fat (oil) phase.

$(C)$ The Tyndall effect is a phenomenon where light is scattered by particles in a colloid or a very fine suspension.
$(C)$ Sugar solution is a true solution, which is homogeneous in nature.
Since the particles in a true solution are too small to scatter light, the Tyndall effect is not observed in a sugar solution.

(B) Colloidal sols formed by mixing substances in a suitable dispersion medium are called lyophilic sols.
These are quite stable.
They are also known as reversible sols because the dispersion medium can be separated from the colloid by means of physical methods like evaporation.
For example,$gum$,$gelatin$,$starch$,$rubber$,etc.,are lyophilic colloids.

(A) colloidal system is a heterogeneous mixture consisting of two phases: the dispersed phase and the dispersion medium. Therefore,the statement that they always have two phases is correct.

(A) Lyophobic sols are more easily coagulated by the addition of suitable electrolytes.
To prevent the coagulation of a lyophobic sol by the addition of an electrolyte,a small amount of a lyophilic colloid is added to it.
This lyophilic colloid acts as a protective colloid,and its protective power is measured in terms of the Gold number.
Thus,the Gold number is a measure of the protective action of a lyophilic colloid on a lyophobic colloid.

(C) sulphur sol is a lyophobic colloid where the dispersed phase consists of large aggregates of sulphur molecules (like $S_8$ molecules).
These aggregates have a particle size that falls within the colloidal range ($1 \ nm$ to $1000 \ nm$).

(A) The statement which is not relevant in the discussion of colloids is $A$.
Sodium aluminium silicate is used in the softening of hard water,which is a process based on ion exchange (zeolite process),not on colloidal properties.
$B$ is relevant as alum acts as a coagulant.
$C$ is relevant as it involves the coagulation of colloidal water droplets in clouds.
$D$ is relevant as it involves the coagulation of colloidal clay particles by sea water.

(A) Lyophilic sols exhibit a strong affinity for the dispersion medium (water).
Due to this strong interaction and heavy hydration,the surface tension of lyophilic sols is lower than that of pure water $(H_2O)$.

(A) When an excess of electrolyte is added to a colloid,the colloidal particles interact with ions carrying a charge opposite to that present on them.
This causes neutralization of the charge on the colloidal particles,which leads to their coagulation or precipitation.

(D) Colloidal particles can exist in various shapes,including spherical,rod-like,and disc-like structures depending on the nature of the dispersed phase and dispersion medium. Therefore,all of these shapes are possible.

(A) The correct answer is $A$.
$As_2S_3$ is a negatively charged sol.
According to the Hardy-Schulze rule,the coagulation of a colloidal solution is brought about by the addition of an electrolyte containing ions with a charge opposite to that of the colloidal particles.

(D) The color of colloidal solutions depends on the wavelength of light scattered by the dispersed particles.
This wavelength further depends on the size and nature of the particles.
For gold sols,the color varies from red to purple or blue depending on the size of the gold particles formed during the preparation process.

(A) Lyophilic colloids are solvent-attracting colloids.
Gelatin is a protein-based substance that forms a stable colloidal solution when mixed with water,making it a lyophilic colloid.
In contrast,$Sulphur$,$Gold$,and $Carbon$ form lyophobic colloids.

(C) The $Tyndall \ effect$ is the phenomenon in which colloidal particles scatter light in all directions when a beam of light passes through a colloidal solution.

(C) Starch is an example of a hydrophilic colloidal sol.
It has a strong affinity between the dispersed phase and the dispersion medium.
It is a reversible and stable sol.

(C) Arsenious sulphide $(As_2S_3)$ sol is a negatively charged sol.
According to the Hardy-Schulze rule,the coagulating power of an electrolyte depends on the valency of the active ion (the ion with a charge opposite to that of the colloidal particles).
For a negatively charged sol,the coagulating power increases with the increase in the valency of the cation.
The order of valency for the given cations is $Al^{+3} > Ba^{+2} > Na^{+}$.
Therefore,the correct order of coagulation power is $Al^{+3} > Ba^{+2} > Na^{+}$.