A Ziegler-Natta catalyst, named after Karl Ziegler and Giulio Natta, is a catalyst used in the synthesis of polymers of 1-alkenes (alpha-olefins). The catalyst is used for Ziegler - Natta polymerization. The Wacker Oxidation is an industrial process, which allows the synthesis of ethanal from ethene by palladium-catalyzed oxidation with oxygen. The catalyst is used for the Wacker process. The Deacon process is a process used during the manufacture of alkalis (the initial end product was sodium carbonate) by the Leblanc process. The catalyst is used for Deacon's process. The contact process is the current method of producing sulfuric acid in the high concentrations needed for industrial processes. The catalyst is used for the Contact process.
02
PYQ 2016
medium
chemistryID: jee-main
A particular adsorption process has the following characteristics : (i) It arises due to van der Waals forces and (ii) it is reversible. Identify the correct statement that describes the above adsorption process :
1
Enthalpy of adsorption is greater than
2
Energy of activation is low.
3
Adsorption is monolayer.
4
Adsorption increases with increase in temperature.
Official Solution
Correct Option: (2)
In the care of physical Absorption there is almost nil energy of Activation and very low enthalpy change.
03
PYQ 2016
medium
chemistryID: jee-main
Gold numbers of some colloids are : Gelatin : 0.005 - 0.01, Gum Arabic : 0.15 - 0.25; Oleate : 0.04 - 1.0; Starch : 15 - 25. Which among these is a better protective colloid ?
1
Gelatin
2
Gum Arabic
3
Oleate
4
Starch
Official Solution
Correct Option: (1)
Gold number
04
PYQ 2017
medium
chemistryID: jee-main
Among the following, correct statement is :
1
Brownian movement is more pronounced for smaller particles than for bigger-particles.
2
Sols of metal sulphides are lyophilic.
3
Hardy Schulze law states that bigger the size of the ions, the greater is its coagulating power.
4
One would expect charcoal to adsorb chlorine more than hydrogen sulphide.
Official Solution
Correct Option: (1)
Brownian movement is more pronounced for smaller particles than for bigger-particles. The speed of moving particles is inversely proportional to the size of the particles. Higher is the size, lower is the speed. Thus, option A is correct. Lyophobic sols- The colloidal system in which the particles of the dispersed phase have no or very little interactions with the dispersion medium are called lyophobic sols. For example and metal sulphides like . Thus, option B is incorrect. Hardy-Schulze law states that higher the charge of the coagulating ions, greater its coagulating power, having opposite sign of solution. This law takes into consideration only the charge carried by an ion, not its size. Thus, option C is incorrect. Easily liquefiable gases are readily adsorbed than gases which do not liquefy easily. Easily liquefiable gases have higher critical temperature and stronger Vander Waals forces of attraction. Thus, option D is incorrect.
05
PYQ 2018
medium
chemistryID: jee-main
Which of the following statements about colloids is False?
1
Freezing point of colloidal solution is lower than true solution at same concentration of a solute.
2
Colloidal particles can pass through ordinary filter paper.
3
When silver nitrate solution is added to potassium iodide solution, a negatively charged colloidal solution is formed.
4
When excess of electrolyte is added to colloidal solution, colloidal particle will be precipitated.
Official Solution
Correct Option: (1)
Freezing point is a colligative property. The colligative properties are properties that depend only on the number of solute particles in a solution, but are independent of the nature of those particles. Therefore, freezing point of colloidal solution will be same as that of true solution at same concentration of a solute.
So, the correct option is (A): Freezing point of colloidal solution is lower than true solution at same concentration of a solute.
06
PYQ 2018
medium
chemistryID: jee-main
Which one of the following is not a property of physical adsorption?
1
Higher the pressure, more the adsorption
2
Lower the temperature, more the adsorption
3
Greater the surface area, more the adsorption
4
Unilayer adsorption occurs
Official Solution
Correct Option: (4)
In physical adsorption, forces of attraction involved between adsorbent and adsorbate are weak, long-range van der Waals forces. The adsorption is generally multilayered.
So, the correct option is (D): Unilayer adsorption occurs.
07
PYQ 2019
medium
chemistryID: jee-main
For coagulation of arscnious sulphide sol, which one of the following salt solution will be most effective ?
1
2
3
4
Official Solution
Correct Option: (1)
Sulphide is charged colloid so cation with maximum charge will be most effective for coagulation. coagulating power.
08
PYQ 2019
medium
chemistryID: jee-main
Haemoglobin and gold sol are examples of :
1
negatively charged sols
2
positively charged sols]
3
negatively and positively charged sols, respectively
4
positively and negatively charged sols, respectively
Official Solution
Correct Option: (4)
09
PYQ 2019
medium
chemistryID: jee-main
An example of solid sol is :
1
Butter
2
Gem stones
3
Paint
4
Hair cream
Official Solution
Correct Option: (2)
Solid sol is the colloidal dispersion which is solid in the state but is little soft. When they are boiled for min, they become softer.
10
PYQ 2020
hard
chemistryID: jee-main
A sample of red ink (a colloidal suspension) is prepared by mixing eosin dye, egg white, and water. The component which ensures stability of the ink sample is :-
1
2
Eosin dye
3
Egg white
4
Water
Official Solution
Correct Option: (3)
The component which ensures the stability of the ink sample is egg white
11
PYQ 2020
medium
chemistryID: jee-main
Kraft temperature is the temperature
1
below which the formation of micelles takes place.
2
below which the aqueous solution of detergents starts freezing.
3
above which the formation of micelles takes place.
4
above which the aqueous solution of detergents starts boiling.
Official Solution
Correct Option: (3)
Kraft temperature is temperature above which formation of micelles takes place
12
PYQ 2021
medium
chemistryID: jee-main
Which one of the following is correct for the adsorption of a gas at a given temperature on a solid surface ?
1
2
3
4
Official Solution
Correct Option: (4)
Step 1: Understanding the Concept:
Adsorption is a spontaneous process where molecules of a gas or liquid accumulate on the surface of a solid. Spontaneity and the physical nature of the process determine the signs of thermodynamic variables. Step 2: Detailed Explanation:
1. Enthalpy ( ): Adsorption involves the formation of new attractions (bonds or van der Waals forces) between the adsorbate and adsorbent. Bond formation is an exothermic process, so energy is released. Thus, .
2. Entropy ( ): In the gas phase, molecules have high degrees of freedom and randomness. When they are adsorbed onto a solid surface, their movement becomes restricted, leading to a decrease in randomness. Thus, .
3. Gibbs Free Energy ( ): For the process to be spontaneous, must be negative. Since , and is negative (making positive), must be sufficiently negative to make negative. Step 3: Final Answer:
The correct thermodynamic parameters for adsorption are and .
13
PYQ 2021
medium
chemistryID: jee-main
Lyophilic sols are more stable than lyophobic sols because,
1
the colloidal particles have positive charge.
2
the colloidal particles have no charge.
3
the colloidal particles are solvated.
4
there is a strong electrostatic repulsion between the negatively charged colloidal particles.
Official Solution
Correct Option: (3)
Step 1: Understanding the Question:
The question asks for the primary reason why lyophilic sols exhibit greater stability compared to lyophobic sols. Step 2: Detailed Explanation:
The stability of a colloidal sol depends on a few factors. Let's analyze both types of sols: Lyophobic Sols (Solvent-Hating):
In these sols, there is little to no affinity between the dispersed phase particles and the dispersion medium. Their stability arises almost entirely from the presence of a like charge (either positive or negative) on all the colloidal particles. This charge leads to electrostatic repulsion between the particles, preventing them from aggregating and settling down. Lyophilic Sols (Solvent-Loving):
In these sols, the dispersed phase particles have a strong affinity for the dispersion medium. Their stability is due to two main factors:
1. Charge: Like lyophobic sols, these particles also carry a charge, which causes mutual repulsion.
2. Solvation: Due to the strong affinity, the particles become extensively solvated, meaning they are surrounded by a protective layer of solvent molecules. This solvation layer acts as a physical barrier that prevents the particles from coming into direct contact and coagulating. Conclusion:
While both types of sols can be stabilized by charge, lyophilic sols have an additional and very significant stabilizing factor: solvation. This is the key reason for their superior stability compared to lyophobic sols. Step 3: Final Answer:
Lyophilic sols are more stable because the colloidal particles are extensively solvated, which provides an extra layer of protection against coagulation.
14
PYQ 2021
medium
chemistryID: jee-main
The sol given below with negatively charged colloidal particles is :
1
KI added to AgNO solution
2
AgNO added to KI solution
3
FeCl added to hot water
4
Al O .xH O in water
Official Solution
Correct Option: (2)
Step 1: Understanding the Question:
We need to identify which of the given preparation methods results in a colloidal solution (sol) where the colloidal particles have a negative charge. Step 2: Key Formula or Approach:
The charge on colloidal particles is due to the preferential adsorption of ions from the dispersion medium that are common to the crystal lattice of the colloidal particle. When a colloid is formed by a chemical reaction, the charge is determined by which reactant is in excess. Step 3: Detailed Explanation:
The formation of silver iodide (AgI) sol occurs from the reaction: . (A) KI added to AgNO solution: In this case, AgNO is the dispersion medium and is in excess. The AgI particles will be surrounded by excess Ag and NO ions. The Ag ion is common to the AgI lattice, so it will be preferentially adsorbed on the surface of the AgI particles. This results in a positively charged sol: [AgI]Ag . (B) AgNO added to KI solution: Here, KI is the dispersion medium and is in excess. The AgI particles will be surrounded by excess K and I ions. The I ion is common to the AgI lattice, so it will be preferentially adsorbed. This results in a negatively charged sol: [AgI]I . (C) FeCl added to hot water: This process involves the hydrolysis of FeCl to form a hydrated ferric oxide sol, Fe O .xH O. This sol is positively charged due to the adsorption of Fe ions from the solution: [Fe O .xH O]Fe . (D) Al O .xH O in water: Hydrated alumina sol is also a positively charged sol. Step 4: Final Answer:
The method that produces a negatively charged sol is adding silver nitrate solution to a potassium iodide solution. This corresponds to option (B).
15
PYQ 2021
medium
chemistryID: jee-main
Tyndall effect is more effectively shown by:
1
true solution
2
lyophilic colloid
3
lyophobic colloid
4
suspension
Official Solution
Correct Option: (3)
Step 1: Understanding the Question:
The question asks which type of mixture shows the Tyndall effect most effectively. Step 2: Key Formula or Approach:
The Tyndall effect is the scattering of light by particles in a colloid or a very fine suspension. The visibility of the effect depends on two main conditions:
1. The diameter of the dispersed particles should not be much smaller than the wavelength of the light used.
2. There must be a significant difference in the refractive indices of the dispersed phase and the dispersion medium. Step 3: Detailed Explanation:
Let's analyze the options:
(A) True solution: The solute particles (ions or small molecules) are too small (less than 1 nm) to scatter light. Hence, true solutions do not show the Tyndall effect.
(B) Lyophilic colloid: (Solvent-loving) In these colloids, the dispersed particles are extensively solvated. There is a strong affinity between the dispersed phase and the dispersion medium. This leads to a small difference in their refractive indices. As a result, the scattering of light is weak, and the Tyndall effect is less pronounced.
(C) Lyophobic colloid: (Solvent-hating) In these colloids, there is very little affinity between the dispersed phase and the dispersion medium. The particles are not well-solvated. This creates a large difference between the refractive indices of the particles and the medium. This large difference causes strong scattering of light, making the Tyndall effect very distinct and effectively shown.
(D) Suspension: Particles in a suspension are large (>1000 nm). They can scatter light, but they are also unstable and settle down under gravity. While they show the effect, the term "colloid" is where the Tyndall effect is a defining characteristic. Between the two types of colloids, lyophobic is the better answer. Step 4: Final Answer:
The Tyndall effect is shown most effectively by lyophobic colloids due to the large difference in refractive indices between the dispersed phase and the dispersion medium.
16
PYQ 2021
medium
chemistryID: jee-main
is adsorbed on 1 g charcoal at following the Freundlich adsorption isotherm. 10.0 mL of is adsorbed at 100 mm of Hg, whereas 15.0 mL is adsorbed at 200 mm of Hg. The volume of adsorbed at 300 mm of Hg is mL. The value of is ________ . (Nearest integer) [Use ]
Official Solution
Correct Option: (1)
Step 1: Understanding the Concept: The Freundlich adsorption isotherm relates the amount of gas adsorbed to the pressure of the gas at a constant temperature: . Since the mass of charcoal is constant, we can use volume ( ) as proportional to the amount adsorbed ( ). Step 2: Detailed Explanation: 1. Let the relation be . - At 100 mm: - At 200 mm: 2. Divide (ii) by (i):
3. Find volume at 300 mm:
Divide by (i):
4. Since , then .
5. Express as :
Step 3: Final Answer: The value of is 128.
17
PYQ 2021
medium
chemistryID: jee-main
Select the graph that correctly describes the adsorption isotherms at two temperatures and ( ) for a gas : (x - mass of the gas adsorbed, m - mass of adsorbent, P - pressure)
1
A
2
B
3
C
4
D
Official Solution
Correct Option: (1)
Step 1: Understanding the Concept: Adsorption of gases on solids (physisorption) is an exothermic process. According to Le Chatelier's principle, an increase in temperature shifts the equilibrium in the direction that absorbs heat (desorption). Step 2: Detailed Explanation: 1. Effect of Temperature: At a given pressure, the amount of gas adsorbed ( ) decreases with an increase in temperature. 2. Analyzing the Condition: We are given . This means is the lower temperature and is the higher temperature. 3. Graph behavior: For any specific pressure , the extent of adsorption at the lower temperature ( ) must be higher than at the higher temperature ( ). 4. Visualizing: On a plot of vs , the curve for the lower temperature ( ) will always lie above the curve for the higher temperature ( ). Step 3: Final Answer: Graph (A) correctly shows the isotherm positioned above the isotherm for all values of .
18
PYQ 2021
medium
chemistryID: jee-main
In Freundlich adsorption isotherm at moderate pressure, the extent of adsorption is directly proportional to . The value of x is :
1
1
2
zero
3
4
Official Solution
Correct Option: (4)
Step 1: The Freundlich adsorption isotherm equation is .
Step 2: In this equation, is a constant that depends on the nature of the adsorbent and the gas at a particular temperature.
Step 3: The value of typically ranges from 0 to 1.
Step 4: Comparing the general form with , we find that .
19
PYQ 2021
medium
chemistryID: jee-main
Sodium stearate is an anionic surfactant which forms micelles in water. Choose the correct statement for it from the following :
1
It forms spherical micelles with group pointing outwards on the surface of sphere.
2
It forms non-spherical micelles with group pointing outwards on the surface.
3
It forms spherical micelles with group pointing towards the centre of sphere.
4
It forms non-spherical micelles with group pointing towards the centre.
Official Solution
Correct Option: (3)
Step 1: Understanding the Concept: Surfactants are molecules with a hydrophilic (polar) head and a hydrophobic (non-polar) tail. In water, these molecules aggregate into micelles to minimize the energy of the system. Step 2: Detailed Explanation: In sodium stearate: 1. is a long hydrocarbon chain (non-polar, hydrophobic tail). 2. is the polar hydrophilic head. When placed in water, the hydrophobic tails cluster together in the interior of the micelle to avoid water molecules, while the hydrophilic heads face outwards to interact with water. This aggregation typically forms a spherical structure. Therefore, the hydrocarbon groups point towards the center of the sphere. Step 3: Final Answer: Statement (C) is correct.
20
PYQ 2021
medium
chemistryID: jee-main
In Freundlich adsorption isotherm, slope of AB line is :
1
n with (n, 0.1 to 0.5)
2
log n with (n>1)
3
log 1/n with (n<1)
4
1/n with (1/n = 0 to 1)
Official Solution
Correct Option: (4)
Step 1: The Freundlich equation is .
Step 2: Taking log on both sides: .
Step 3: Comparing with , the slope is .
Step 4: Experimentally, the value of ranges from 0 to 1.
21
PYQ 2021
medium
chemistryID: jee-main
Match List - I with List - II :List - I (Process)
(a) Deacon's process
(b) Contact process
(c) Cracking of hydrocarbons
(d) Hydrogenation of vegetable oils List - II (Catalyst)
(i) ZSM-5
(ii) CuCl₂
(iii) Particles 'Ni'
(iv) V₂O₅
1
(a)-(i), (b)-(iii), (c)-(ii), (d)-(iv)
2
(a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)
3
(a)-(iii), (b)-(iv), (c)-(i), (d)-(ii)
4
(a)-(ii), (b)-(iv), (c)-(i), (d)-(iii)
Official Solution
Correct Option: (4)
Step 1: **Deacon's process** (Cl₂ production) uses as a catalyst.
Step 2: **Contact process** (H₂SO₄ production) uses as a catalyst.
Step 3: **Cracking of hydrocarbons** (specifically methanol to gasoline) uses the zeolite **ZSM-5**.
Step 4: **Hydrogenation** of oils uses finely divided **Nickel (Ni)**.
22
PYQ 2021
medium
chemistryID: jee-main
Given below are two statements : one is labelled as Assertion A and the other is labelled as Reason R. Assertion A : SO (g) is adsorbed to a larger extent than H (g) on activated charcoal. Reason R : SO (g) has a higher critical temperature than H (g). In the light of the above statements, choose the most appropriate answer from the options given below.
1
Both A and R are correct and R is the correct explanation of A.
2
Both A and R are correct but R is not the correct explanation of A.
3
A is correct but R is not correct.
4
A is not correct but R is correct.
Official Solution
Correct Option: (1)
Let's analyze the assertion and the reason. Assertion A: SO (g) is adsorbed to a larger extent than H (g) on activated charcoal. This is a factual statement. The extent of physisorption of a gas depends on its nature. Reason R: SO (g) has a higher critical temperature than H (g). The critical temperature ( ) is the temperature above which a gas cannot be liquefied, no matter how much pressure is applied.
of SO is 430 K (157 C).
of H is 33 K (-240 C).
So, the reason is also a correct factual statement. Now, let's establish the link. The ease of liquefaction of a gas is directly related to its critical temperature. A gas with a higher critical temperature has stronger intermolecular forces and can be liquefied more easily. Gases that are more easily liquefiable are also more readily adsorbed on the surface of a solid adsorbent (like activated charcoal). Since SO has a much higher critical temperature than H , it is more easily liquefiable and thus adsorbed to a much larger extent. Therefore, both Assertion A and Reason R are correct, and Reason R is the correct explanation for Assertion A.
23
PYQ 2021
medium
chemistryID: jee-main
Most suitable salt which can be used for efficient clotting of blood will be :
1
NaHCO₃
2
Mg(HCO₃)₂
3
FeCl₃
4
FeSO₄
Official Solution
Correct Option: (3)
Step 1: Blood is a negatively charged colloidal solution (sol).
Step 2: According to the Hardy-Schulze rule, the coagulating power of an electrolyte is directly proportional to the fourth power of the valency of the active ion.
Step 3: Among the options, (from ) has the highest positive charge compared to , , and .
Step 4: Therefore, is the most effective at neutralizing the negative charge on blood particles, causing rapid clotting (coagulation).
24
PYQ 2021
medium
chemistryID: jee-main
Which one of the following statements is FALSE for hydrophilic sols?
1
They do not require electrolytes for stability.
2
These sols are reversible in nature.
3
Their viscosity is of the order of that of H O.
4
The sols cannot be easily coagulated.
Official Solution
Correct Option: (3)
Let's analyze the properties of hydrophilic (lyophilic) sols. These are colloids where the dispersed phase has a strong affinity for the dispersion medium (e.g., starch in water). (A) They do not require electrolytes for stability: This is TRUE. Hydrophilic sols are stabilized primarily by the solvation (hydration) layer around the colloidal particles, which prevents them from aggregating. (B) These sols are reversible in nature: This is TRUE. If the dispersion medium is evaporated, the sol can be reconstituted by simply adding the medium back and shaking. (C) Their viscosity is of the order of that of H O: This is FALSE. Due to the strong interaction and extensive solvation between the dispersed particles and the medium, hydrophilic sols are much more viscous than the dispersion medium itself. In contrast, lyophobic sols have a viscosity that is nearly the same as the medium. (D) The sols cannot be easily coagulated: This is TRUE. Because of their high stability from solvation, they require a large amount of electrolyte to cause coagulation (salting out). The false statement is (C).
25
PYQ 2021
easy
chemistryID: jee-main
gas adsorbs on charcoal following Freundlich adsorption isotherm. For a given amount of charcoal, the mass of adsorbed becomes 64 times when the pressure of is doubled. The value of n in the Freundlich isotherm equation is _________ . (Round off to the Nearest Integer)
Official Solution
Correct Option: (1)
26
PYQ 2021
medium
chemistryID: jee-main
The charges on the colloidal CdS sol and TiO₂ sol are, respectively :
1
positive and positive
2
negative and positive
3
positive and negative
4
negative and negative
Official Solution
Correct Option: (2)
Step 1: Metallic sulfides generally form negatively charged sols. Therefore, CdS (Cadmium Sulfide) sol is negative.
Step 2: Metal oxides and hydrated metallic oxides generally form positively charged sols. Therefore, sol is positive.
27
PYQ 2022
medium
chemistryID: jee-main
Which of the following can be used to prevent the decomposition of ?
1
Urea
2
Formaldehyde
3
Formic acid
4
Ethanol
Official Solution
Correct Option: (1)
The correct option is (A): Urea.
28
PYQ 2022
medium
chemistryID: jee-main
Incorrect statement for Tyndall effect is:
1
The refractive indices of the dispersed phase and the dispersion medium differ greatly in magnitude.
2
The diameter of the dispersed particles is much smaller than the wavelength of the light used.
3
During projection of movies in the cinemas hall, Tyndall effect is noticed.
4
It is used to distinguish a true solution from a colloidal solution.
Official Solution
Correct Option: (2)
For Tyndall effect, the diameter of the dispersed particles is not much smaller than the wavelength of the light used. So, the correct option is (B): The diameter of the dispersed particles is much smaller than the wavelength of the light used.
29
PYQ 2022
medium
chemistryID: jee-main
Among the following the number of curves not in accordance with Freundlich adsorption isotherm is____.
Official Solution
Correct Option: (1)
Correct answer is 3
30
PYQ 2023
easy
chemistryID: jee-main
Match the terms in Column-I with their description in Column-II and choose the correct option:
Column I (Chemical reactions)
Column II (Enzymes used)
(i)
Glucose → CO2 + Ethanol
a
Pepsin
(ii)
Sucrose→Glucose + Fructose
b
Diastase
(iii)
Starch →Maltose
c
Zymase
(iv)
Protein→Amino acids
d
Invertase
1
i c, ii d, iii b, iv a
2
i d, ii c, iii b, iv a
3
i c, ii d, iii a, iv b
4
i c, ii b, iii d, iv a
Official Solution
Correct Option: (1)
The correct answer is A:
Glucose CO2 + Ethanol Zymase
Sucrose Glucose + Fructose Invertase
Starch Maltose Diastase
Protein Amino acids Pepsin
31
PYQ 2023
medium
chemistryID: jee-main
What happens when lyophilic sol is added to lyophobic sol. prevention from coagulation precipitation emulsion electrophoresis
1
Prevention from coagulation
2
Precipitation
3
Emulsion
4
Electrophoresis
Official Solution
Correct Option: (1)
When a lyophilic sol is added to a lyophobic sol, the lyophilic sol tends to form a protective film over the lyophobic sol. This film prevents the lyophobic sol particles from coagulating by providing a barrier, thereby stabilizing the sol.
32
PYQ 2023
medium
chemistryID: jee-main
During bleeding from cut is used to stop bleeding as
1
Cl– cause coagulation
2
Ferric ion cause coagulation
3
dilutes blood
4
Bleeding does not stop
Official Solution
Correct Option: (2)
The correct option is (B): Ferric ion cause coagulation
Fe+2 ion coagulate blood which is colloid.
33
PYQ 2023
medium
chemistryID: jee-main
The enthalpy change for the adsorption process and micelle for mation respectively are
1
2
3
4
Official Solution
Correct Option: (3)
Adsorption: Adsorption is an exothermic process . Energy is released when molecules adhere to a surface. Micelle Formation: Micelle formation is an endothermic process . Energy is required to overcome the repulsion between the hydrophobic tails of the surfactant molecules as they aggregate to form micelles.
34
PYQ 2023
medium
chemistryID: jee-main
Which compound is added to cement to increase its setting time?
1
Gypsum
2
Lime stone
3
Clay
4
Calcium carbonate
Official Solution
Correct Option: (1)
Gypsum (CaSO4·2H2O)
Explanation:
When cement is mixed with water, the setting process begins due to hydration reactions of the compounds present in cement, especially tricalcium aluminate (C3A).
These reactions occur rapidly, leading to a very quick setting of cement, which can make it difficult to work with during construction.
Gypsum, which is chemically calcium sulfate dihydrate (CaSO4·2H2O), is added to cement to regulate the setting time.
Gypsum slows down the hydration of tricalcium aluminate (C3A) by forming a coating around the particles, giving more time for mixing, transportation, and placing of the cement.
Conclusion:
Gypsum is added to cement to increase its setting time and make it workable during construction.
35
PYQ 2023
medium
chemistryID: jee-main
Thin layer chromatography of a mixture shows the following observation:
The correct order of elution in the silica gel column chromatography is .
1
A>B>C
2
C>A>B
3
A>C>B
4
B>C>A
Official Solution
Correct Option: (3)
According to the observation, A is more mobile and interacts with the mobile phase more than C, and C is more than B.
This suggests that A is more mobile, C is less mobile, and B has the least mobility. Hence the correct order is A>C>B.
36
PYQ 2023
medium
chemistryID: jee-main
Given below are two statements: one is labelled as Assertion (A) and the other is labelled as Reason (R). Assertion (A): In expensive scientific instruments, silica gel is kept in watch-glasses or in semipermeable membrane bags. Reason (R): Silica gel adsorbs moisture from air via adsorption, thus protects the instrument from water corrosion (rusting) and/or prevents malfunctioning. In the light of the above statements, choose the correct answer from the options given below:
1
A is false but (R) is true
2
Both (A) and (R) are true and (R) is the correct explanation of (A)
3
A is true but (R) is false
4
Both (A) and (R) are true but (R) is not the correct explanation of (A)
Official Solution
Correct Option: (2)
Silica gel is commonly used in expensive scientific instruments to prevent moisture from damaging the instruments. It adsorbs moisture from the air, preventing water corrosion (rusting) and protecting the instrument from malfunctioning. Thus, the reason given in (R) provides the correct explanation for the assertion in (A).
37
PYQ 2023
medium
chemistryID: jee-main
The number of correct statements about modern adsorption theory of heterogeneous catalysis from the following is _______ A. The catalyst is diffused over the surface of reactants. B. Reactants are adsorbed on the surface of the catalyst. C. Occurrence of chemical reaction on the catalysts surface through formation of an intermediate. D. It is a combination of intermediate compound formation theory and the old adsorption theory E. It explains the action of the catalyst as well as those of catalytic promoters and poisons.
Official Solution
Correct Option: (1)
A. The catalyst is diffused over the surface of reactants.
This statement is incorrect. In heterogeneous catalysis, the catalyst is in a different phase than the reactants. The reactants are adsorbed onto the surface of the catalyst, not the other way around.
B. Reactants are adsorbed on the surface of the catalyst.
This statement is correct. Adsorption of reactants on the catalyst surface is a crucial step in heterogeneous catalysis.
C. Occurrence of chemical reaction on the catalyst’s surface through formation of an intermediate.
This statement is correct. The reactants form an intermediate compound with the catalyst on the surface, which subsequently decomposes to form the products.
D. It is a combination of intermediate compound formation theory and the old adsorption theory.
This statement is correct. The modern adsorption theory combines the concepts of intermediate formation and the old adsorption theory to explain the catalytic process.
E. It explains the action of the catalyst as well as those of catalytic promoters and poisons.
This statement is incorrect. While the modern adsorption theory explains the roles of promoters and poisons, the statement oversimplifies the theory and its application.
Final Answer:
The number of correct statements is 3 (B, C, and D).
38
PYQ 2023
hard
chemistryID: jee-main
A metal surface of 100 cm2 area has to be coated with nickel layer of thickness 0.001mm. A current of 2A was passed through a solution of Ni (NO3)2 for 'x' seconds to coat the desired layer. The value of x is_____ (Nearest integer) (PNi (density of Nickel) is 10 gmL-1, Molar mass of Nickel is 60 gmol-1 F = 96500 C mol-1)
Official Solution
Correct Option: (1)
Solution: To find the time required to coat the metal surface, we use Faraday's law of electrolysis: where:
is the mass of the substance deposited,
is the molar mass of the substance (nickel, 60 g/mol),
is the current (2 A),
is the time in seconds,
is the valency of the substance (for nickel, ),
is the Faraday constant (96500 C/mol).
We are given that the thickness of the nickel layer is 0.001 mm (0.0001 cm), so the volume of the nickel deposited is: Using the density of nickel , we can calculate the mass of the deposited nickel: Now, substitute into Faraday’s equation: Solving for : Thus, the time required to coat the desired layer is approximately 161 seconds.
39
PYQ 2024
medium
chemistryID: jee-main
In the given TLC, the distance of spot and are 5 cm and 7 cm, from the bottom of the TLC plate, respectively. The value of is times more than . The value of is _________ .
Official Solution
Correct Option: (1)
The value, or retention factor, is defined as the ratio of the distance traveled by the compound to the distance traveled by the solvent front. Here, the solvent front moves 10 cm. Let's calculate the values for spots and :
According to the problem, is times greater than . Therefore:
Solving for :
Thus, the value of is 14, which falls within the given range of 15,15.
40
PYQ 2024
medium
chemistryID: jee-main
Adsorption' principle is used for which of the following purification method?
1
Extraction
2
Chromatography
3
Distillation
4
Sublimation
Official Solution
Correct Option: (2)
To solve this question, we need to understand the principle of adsorption and the methods mentioned in the options.
Adsorption Principle: Adsorption is the process by which atoms, ions, or molecules from a substance (usually a gas, liquid, or dissolved solid) adhere to a surface of the adsorbent. This process is utilized in various purification techniques where substances are selectively retained on the surface of the adsorbent material.
Now, let's evaluate each of the given options:
Extraction: This is a separation process where a substance is separated from a mixture using a solvent. It does not primarily rely on adsorption.
Chromatography: This method involves the separation of components in a mixture based on their differing velocities through a medium under the influence of a solvent. The principle of adsorption is heavily involved as different substances adhere to the stationary phase to varying extents, thus causing separation.
Distillation: This is a method of separating mixtures based on differences in their volatilities in a boiling liquid mixture. It is not based on adsorption.
Sublimation: Sublimation involves a solid changing directly to gas without passing through a liquid phase. Adsorption does not play a role in this process.
Conclusion: Among the given options, Chromatography is the method that relies on the principle of adsorption for purification. The stationary phase in chromatography adsorbs different components of the mixture to different extents, allowing separation and purification of the components.
41
PYQ 2024
medium
chemistryID: jee-main
The adsorbent used in adsorption chromatography is/are A. silica gel B. alumina C. quick lime D. magnesia Choose the most appropriate answer from the options given below :
1
B only
2
C and D only
3
A and B only
4
A only
Official Solution
Correct Option: (3)
The most common polar and acidic support used in adsorption chromatography is silica. The surface silanol groups present on silica effectively adsorb polar compounds, making it particularly well-suited for basic substances. Alumina, being polar and basic, is also widely used as an adsorbent in adsorption chromatography. Together, these make the pair of adsorbents utilized frequently for such purposes.
42
PYQ 2026
hard
chemistryID: jee-main
The half-life of Zn is 245 days. After days, 75% of the original activity remained. The value of in days is __________ (Nearest integer).} (Given: and )
Official Solution
Correct Option: (1)
Step 1: Using radioactive decay law.
Here, remaining activity = 75% = 0.75, half-life days, and time = days. Step 2: Substituting values.
Taking logarithm on both sides:
Step 3: Simplifying logarithms.
Also,
Step 4: Solving for .
Step 5: Conclusion. The value of is approximately 102 days.
