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

(D) $I$. The size of colloidal particles is larger than the size of the pores present in the membrane. Hence,colloidal particles cannot pass through the membrane.
$II$. Animal bladder can be used as a semi-permeable membrane.
$III$. Cellophane is a thin transparent sheet made of cellulose and is commonly used as a membrane for dialysis.
$IV$. Ions or small molecules (crystalloids) can easily diffuse through the membrane into the surrounding water.
Therefore,the correct statements are $II$ and $IV$.

(C) The protective power of a lyophilic colloidal sol is expressed in terms of $Gold \ number$.
Gold number is defined as the minimum amount of protective colloid in milligrams that must be added to $10 \ mL$ of a standard red gold sol to prevent its coagulation when $1 \ mL$ of a $10\% \ NaCl$ solution is added to it.
Smaller the gold number,higher is the protective power of the colloid.

(B) At high concentrations,soap molecules in water aggregate to form clusters known as micelles. These aggregates of particles are classified as $associated \ colloids$.

(B) Arsenic sulphide solution $(As_2S_3)$ is a hydrophobic sol,meaning it has little or no affinity for the dispersion medium $(H_2O)$.
Conversely,solutions of gum,starch,and protein are hydrophilic in nature because they are macromolecules (natural polymers) that have a strong affinity for the dispersion medium.

(C) Among the given statements,only statement $(c)$ is incorrect.
The layer of positive or negative charge acquired by selective adsorption of ions on the surface of a colloidal particle is known as the adsorption layer.
The electrokinetic potential or zeta potential is defined as the potential difference between the fixed layer and the diffused layer of opposite charge.

(A) The classification of colloidal systems based on the physical state of the dispersed phase and dispersion medium is as follows:
$(A)$ Solid dispersed in liquid is called a $Sol$ $(IV)$.
$(B)$ Liquid dispersed in liquid is called an $Emulsion$ $(I)$.
$(C)$ Gas dispersed in liquid is called $Foam$ $(II)$.
$(D)$ Liquid dispersed in solid is called a $Gel$ $(III)$.
Therefore,the correct match is $A-IV, B-I, C-II, D-III$.

(C) lyophobic colloid is one in which the dispersed phase has little or no affinity for the dispersion medium.
$Gold$ sol is a classic example of a lyophobic sol because the gold particles do not have a strong attraction to the water molecules.
Consequently,these sols are unstable and can be easily coagulated by the addition of small amounts of electrolytes.

(C) Bredig's arc method is a common technique used for the preparation of colloidal sols of metals like gold,silver,and platinum.
In this method,an electric arc is struck between metal electrodes immersed in a dispersion medium (like water) stabilized by an ice bath.
The intense heat of the arc vaporizes the metal (dispersion),and the cold surrounding medium causes the metal vapors to condense into colloidal-sized particles (condensation).
Therefore,Statement-$I$ is correct,and Statement-$II$ is incorrect because the process involves both dispersion and condensation.

(B) The process of converting a freshly prepared precipitate into a colloidal sol by shaking it with a dispersion medium in the presence of a small amount of electrolyte is called peptisation.
Other options like $i$. Dialysis,$ii$. Electrodialysis,$iii$. Ultrafiltration,and $iv$. Ultra-centrifugation are methods used for the purification of colloidal solutions,not for their preparation.

(B) The process of converting a freshly prepared precipitate into a colloidal solution by adding a suitable electrolyte (called a peptizing agent) is known as $Peptization$.
The reverse process,where a colloidal solution is converted into a precipitate by adding an electrolyte,is known as $Coagulation$ or $Flocculation$.
$Precipitate \xrightarrow{\text{Peptization}} \text{Colloidal solution}$
$\text{Colloidal solution} \xrightarrow{\text{Coagulation/Flocculation}} \text{Precipitate}$

(D) Colloidal solutions can be purified by $dialysis$.
It is a process of separating a crystalloid from a colloid by diffusion or filtration through a semi-permeable membrane.
The process of dialysis can be quickened by applying an electric field,which is known as electrodialysis.

(A) $CMC$ is defined as the concentration of surfactants above which micelles form and all additional surfactants added to the system will form micelles.
Concentration of surfactant is nearly $10^{-4}$ to $10^{-3} \ mol \ L^{-1}$ at $CMC$.
$CMC$ depends on temperature,pressure,and the concentration of other surface-active substances and electrolytes.

(A) mixture of $N_2$ and $O_2$ gases at room temperature forms a homogeneous gaseous mixture,not an aerosol. An aerosol is a colloidal system where a solid or liquid is dispersed in a gas.
$(B)$ Lyophilic sols are inherently more stable than lyophobic sols because they have a high affinity between the dispersed phase and the dispersion medium.
$(C)$ Micelles are formed only at or above the Kraft temperature $(T_k)$ and above the Critical Micelle Concentration $(CMC)$.
$(D)$ Sodium stearate $(C_{17}H_{35}COONa)$ is a common soap,and sodium lauryl sulphate $(CH_3(CH_2)_{11}SO_4^-Na^+)$ is a common synthetic detergent.

(B) At a particular concentration of surfactants,micelle formation takes place.
To reach this concentration,a specific temperature is required,which is called the $Kraft$ temperature.
Below the $Kraft$ temperature,the surfactant does not form micelles.

(A) $Fe_2O_3 \cdot xH_2O$ 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). The higher the valency of the flocculating ion,the greater is its coagulating power. The anions provided are: $Cl^-$ (valency $1$),$[Fe(CN)_6]^{4-}$ (valency $4$),$PO_4^{3-}$ (valency $3$),and $SO_4^{2-}$ (valency $2$). Comparing the valencies: $4 > 3 > 2 > 1$. Thus,the order of coagulating power is: $[Fe(CN)_6]^{4-} > PO_4^{3-} > SO_4^{2-} > Cl^-$. This corresponds to the beakers: $II > III > IV > I$.

(D) According to the Hardy-Schulze rule,the coagulating power of an ion is directly proportional to the magnitude of its charge.
For a positively charged sol,the coagulating power of anions follows the order: $\left[Fe(CN)_6\right]^{4-} > PO_4^{3-} > SO_4^{2-} > Cl^{-}$.
Therefore,$\left[Fe(CN)_6\right]^{4-}$ has the maximum coagulating power.

(D) The gold number is defined as the minimum weight of a protective colloid in milligrams that must be added to $10 \ mL$ of a standard gold sol to prevent its coagulation when $1 \ mL$ of a $10 \% NaCl$ solution is added.
From the given table,we observe the weights of $X$ added:
- At $23 \ mg$ and $24 \ mg$,coagulation is not prevented.
- At $25 \ mg$,$26 \ mg$,and $27 \ mg$,coagulation is prevented.
The minimum weight of $X$ required to prevent coagulation is $25 \ mg$.
Therefore,the gold number of $X$ is $25$.

(C) $1$. $S_8$ sulphur sol consists of particles containing a thousand or more $S_8$ sulphur molecules,hence it is a multi-molecular colloid.
$2$. Enzymes and proteins are examples of naturally occurring macromolecules,thus they are macro-molecular colloids.
$3$. Starch forms a lyophilic sol with water when heated.
$4$. $As_2S_3$ sol is a negatively charged sol,not positively charged. Therefore,the option $As_2S_3$ sol - positively charged sol is incorrectly matched.

(B) The coagulating value (or flocculation value) is defined as the minimum concentration of an electrolyte in millimoles per liter $(mmol \cdot L^{-1})$ required to cause the precipitation of a sol in $2$ hours.
From the provided data,the minimum concentration required for precipitation is $7 \times 10^{-5} \ mol \cdot L^{-1}$.
To convert this to the coagulating value in $mmol \cdot L^{-1}$:
$\text{Coagulating value} = 7 \times 10^{-5} \ mol \cdot L^{-1} \times 10^3 \ mmol \cdot mol^{-1} = 7 \times 10^{-2} \ mmol \cdot L^{-1}$.

(B) Gold number is defined as the minimum weight in milligrams of a protective colloid required to prevent the coagulation of $10 \text{ mL}$ of a standard gold sol when $1 \text{ mL}$ of $10\% \text{ NaCl}$ solution is added.
From the given data,the weights that prevent coagulation are $40 \text{ mg}$,$35 \text{ mg}$,and $33 \text{ mg}$.
The minimum weight among these that prevents coagulation is $33 \text{ mg}$.
Thus,the gold number of $A$ is $33$.

(B) Blood is a colloidal solution of negatively charged particles.
When a styptic agent like $FeCl_3$ solution is applied,the $Fe^{3+}$ ions neutralize the charge on the blood colloids.
This leads to the coagulation of blood,which forms a clot and stops further bleeding.

(D) The $Hardy-Schulze$ rule states that the coagulating power of an electrolyte depends on the valency of the active ion (flocculating ion) causing coagulation. Higher the valency of the flocculating ion,greater is its power to cause precipitation of a colloid.

(A) Animal skins are colloidal in nature and possess positively charged particles.
When animal skin is soaked in tannin,which contains negatively charged colloidal particles,mutual coagulation occurs.
This process is known as tanning,which hardens the leather.
Since the assertion states the nature of the skin and the reason explains the charge responsible for the tanning process,the reason is the correct explanation for the assertion.

(D) According to the $HARDY-SCHULZE$ law,the coagulating power of an ion is directly proportional to the magnitude of the charge on the ion.
The magnitudes of the charges on the given ions are:
$I. [Fe(CN)_6]^{4-} = 4$
$II. Cl^{-} = 1$
$III. SO_4^{2-} = 2$
Comparing the magnitudes: $4 > 2 > 1$.
Therefore,the correct order of coagulating power is $I > III > II$.

(C) Milk of magnesia is a colloidal suspension of $Mg(OH)_2$ in water.
It is widely used as an antacid to neutralize excess stomach acid and as a saline laxative to treat constipation.

(B) The reaction between $As_2O_3$ and $H_2S$ is a double decomposition reaction used to prepare arsenic sulfide sol.
The balanced chemical equation is:
$As_2O_3 + 3H_2S \rightarrow As_2S_3 (sol) + 3H_2O$
Thus,the sol formed is $As_2S_3$.

(C) Milk is a colloidal system (emulsion) where fat globules are dispersed in water.
When light falls on this mixture,the shorter wavelengths (blue) are scattered more effectively by the colloidal particles due to the $Tyndall \ effect$.
Therefore,when viewed by reflected light,the mixture appears blue.

(A) The balanced chemical equation for the reduction of gold$(III)$ chloride by formaldehyde is:
$2 AuCl_3 + 3 HCHO + 3 H_2 O \longrightarrow 2 Au (\text{sol}) + 3 HCO_2 H + 6 HCl$
Comparing this with the given equation $a AuCl_3 + b HCHO + c H_2 O \longrightarrow x Au + y HCO_2 H + z HCl$,we get:
$a=2, b=3, c=3, x=2, y=3, z=6$.

(B) The aggregate of carboxylate ions of fatty acids forms a spherical shape known as a micelle.
Soap acts as an emulsifier because it reduces surface tension and emulsifies fats and oils by forming micelles around oil droplets.
While both statements are scientifically correct,the formation of a spherical shape (micelle) is a structural property,whereas the emulsification process is a functional application. Therefore,$R$ is not the direct explanation for the formation of the spherical shape itself.
Thus,both $A$ and $R$ are correct but $R$ is not the correct explanation of $A$.

(C) Colloidal particles in a sol carry a specific type of electrical charge.
Positively charged sols include: $TiO_2$,$CdS$,$Fe_2O_3$.
Negatively charged sols include: blood,$Cu$,$Ag$,Clay,$SiO_2$.
Wait,let us re-evaluate the classification:
Positively charged sols: $TiO_2$,$Fe_2O_3$.
Negatively charged sols: blood,$CdS$,$Cu$,$Ag$,Clay,$SiO_2$.
Actually,standard classification is:
Positively charged: $TiO_2$,$Fe_2O_3$.
Negatively charged: blood,$CdS$,$Cu$,$Ag$,Clay,$SiO_2$.
Total positively charged = $2$.
Total negatively charged = $6$.
Therefore,the correct option is $C$.

(B) Brownian movement is the random zig-zag motion of colloidal particles.
According to the Stokes-Einstein equation,the diffusion coefficient $D$ is inversely proportional to the radius of the particle $r$ and the viscosity of the medium $\eta$ $(D \propto \frac{1}{r \eta})$.
Therefore,smaller particle size and lower viscosity of the dispersion medium result in faster Brownian movement.

(D) When a dilute aqueous solution of $AgNO_3$ is added to an excess of dilute $KI$ solution,$AgI$ precipitate is formed.
Since $KI$ is in excess,the $I^{-}$ ions are present in the dispersion medium.
These $I^{-}$ ions are preferentially adsorbed on the surface of the $AgI$ particles,resulting in the formation of a negatively charged colloidal sol represented as $AgI / I^{-}$.

(B) Glycine is an amino acid with an isoelectric point $(pI)$ of $5.97$. At this $pH$,glycine exists as a zwitterion,meaning it has no net charge and does not move towards any electrode in an electric field.
When a base is added,the $pH$ of the solution increases above the $pI$ $(pH > 5.97)$.
In a basic medium,the amino acid loses a proton from the $-NH_3^+$ group,resulting in a net negative charge on the glycine molecule.
Since the colloidal particles become negatively charged,they will move towards the anode under the influence of an electric field.
The movement of negatively charged colloidal particles towards the anode is known as $Anaphoresis$.

(B) $I$. Sulphur sol is a multimolecular colloid because it contains a large number of $S_8$ molecules aggregated together. This statement is correct.
$II$. For the Tyndall effect to be observed,the diameter of the dispersed particles must not be much smaller than the wavelength of the light used. This statement is correct.
$III$. The process of removing a dissolved substance from a colloidal solution by means of diffusion through a suitable membrane is called dialysis,not peptisation. Peptisation is the process of converting a precipitate into a colloidal sol by adding an electrolyte. This statement is incorrect.
$IV$. Eosin and gelatin are examples of negatively charged sols. This statement is correct.
Therefore,the correct statements are $I, II,$ and $IV$. Hence,option $(B)$ is correct.

(B) The colour of colloidal solutions depends on the wavelength of light scattered by the dispersed particles.
In the case of gold sol,the colour changes with the size of the gold particles.
As the particle size increases,the wavelength of the scattered light changes,resulting in different colours like red,purple,blue,and golden.

(B) $1$. $As_2S_3$ is a negatively charged sol,not positively charged. So,option $A$ is incorrect.
$2$. For the Tyndall effect to be observed,the refractive indices of the dispersed phase and the dispersion medium must differ significantly in magnitude. This is a correct statement.
$3$. An ultramicroscope is used to detect the presence of colloidal particles,but it does not provide information about their size and shape. So,option $C$ is incorrect.
$4$. The colour of gold sol depends on the size of the particles. The finest gold sol is red in colour,while coarser sols appear purple or blue. So,option $D$ is incorrect.

(D) Ferric hydroxide solution is a positively charged sol.
According to the Hardy-Schulze rule,the greater the valence of the coagulating ion,the greater is its power to cause coagulation.
$KCl \rightleftarrows K^{+} + Cl^{-}$
$KNO_3 \rightleftarrows K^{+} + NO_3^{-}$
$K_2SO_4 \rightleftarrows 2K^{+} + SO_4^{2-}$
$K_3[Fe(CN)_6] \rightleftarrows 3K^{+} + [Fe(CN)_6]^{3-}$
Since the ferric hydroxide sol is positively charged,it is coagulated by negative ions.
The valency of the negative ion is highest in $[Fe(CN)_6]^{3-}$ (i.e.,$3$).
Hence,$K_3[Fe(CN)_6]$ will be most effective in causing coagulation of ferric hydroxide solution.

(A) The correct matching is:
$A$. Aerosol: $IV$. Smoke (Solid in gas)
$B$. Foam: $II$. Soap lather (Gas in liquid)
$C$. Emulsion: $I$. Milk (Liquid in liquid)
$D$. Gel: $III$. Cheese (Liquid in solid)
Therefore,the correct sequence is $A-IV, B-II, C-I, D-III$.

(A) Photographic plates or films are prepared by coating an emulsion of the light-sensitive $AgBr$ (silver bromide) in gelatin over glass plates or celluloid films.
Light-sensitive properties have allowed silver halides to become the basis of modern photographic materials.
When $AgBr$ is exposed to light,a decomposition reaction occurs,resulting in the formation of metallic silver and bromine gas. This is a photochemical reaction where white $AgBr$ converts into grey-colored silver.

(C) $Lactobacillus$ bacteria convert the lactose sugar present in milk into an acid known as $Lactic \ acid$ through the process of fermentation.

(D) Gold number is defined as the minimum mass of a protective colloid in $mg$ that prevents the coagulation of $10 \ mL$ of a gold sol when $1 \ mL$ of $10 \% NaCl$ solution is added to it.
Given,the gold number of Haemoglobin $= 0.03$.
This means $0.03 \ mg$ of Haemoglobin is required to protect $10 \ mL$ of gold sol against $1 \ mL$ of $10 \% NaCl$.
For $50 \ mL$ of gold sol,the amount of protective colloid required is $5 \times 0.03 \ mg = 0.15 \ mg$.
Since the amount of $NaCl$ added is $5 \ mL$ (which is $5 \times$ the standard amount),the protection required is proportional to the volume of the gold sol.
Thus,the mass of Haemoglobin required is $0.15 \ mg$.

(B) Gold sol is a lyophobic sol,not a lyophilic sol. Therefore,option $B$ is incorrect.

(C) The classification of colloids based on the physical state of the dispersed phase and dispersion medium is as follows:
$1$. $A$. Sol (Solid in Liquid): Example is $Paint$.
$2$. $B$. Foam (Gas in Liquid): Example is $Whipped \ cream$.
$3$. $C$. Gel (Liquid in Solid): Example is $Butter$.
$4$. $D$. Aerosol (Liquid in Gas): Example is $Cloud$.
Therefore,the correct matching is $A-III, B-II, C-IV, D-I$.

(A) . The Tyndall effect is a phenomenon where light is scattered by colloidal particles,which is not observed in true solutions. Thus,it is used to distinguish between them. This statement is correct.
$B$. Zeta potential is the potential difference between the fixed layer and the diffused layer of ions surrounding the colloidal particle,which influences the stability and movement of particles in an electric field. This statement is correct.
$C$. Brownian motion is inversely proportional to the viscosity of the medium. If the viscosity is very high,the Brownian motion becomes slower,not faster. This statement is incorrect.
$D$. Brownian motion is a random zig-zag motion of colloidal particles that prevents them from settling down due to gravity,but it does not stabilize the sol; rather,it is the charge on the particles that provides stability. This statement is incorrect.
Therefore,the correct statements are $A$ and $B$.

(C) $(i)$ Incorrect: $A$ mixture of gases is a true solution,not an aerosol.
$(ii)$ Correct: Milk is an emulsion of liquid fat in water.
$(iii)$ Correct: Smoke is an aerosol (solid particles dispersed in gas).
$(iv)$ Incorrect: Peptisation is a method of preparation of colloidal solutions,not purification.
$(v)$ Correct: Ultrafiltration is a method used for the purification of colloidal solutions by removing electrolytes and other impurities using a special filter paper.
Therefore,statements $(ii)$,$(iii)$,and $(v)$ are correct.

(D) Fog is a dispersion of liquid in gas.
It is a colloidal system where the dispersed phase is liquid and the dispersion medium is gas.

(D) Animal leather is colloidal in nature and consists of positively charged particles.
When it is soaked in tannin,which is a negatively charged colloid,mutual coagulation occurs.
This process leads to the hardening of the leather,a process known as tanning.