Chemistry: CUET Mock Test - 9 - CUET MCQ

Coagulation or precipitation is a process of aggregating together the colloidal particles to change them into large-sized particles which ultimately settle as a precipitate. The different methods to test the type of emulsion are-microscopic, conductance and dye method.

When ethylamine reacts with one mole of hydrochloric acid (HCl), the ammonium salt formed is ethylammonium chloride, which has the chemical formula C₂H₅NH₃⁺Cl^-
The reaction between ethylamine and HCl can be represented as follows:

CH₃CH₂ - NH₂ + HCl →

In this reaction, the HCl protonates the ethylamine to form ethylammonium ion (C2H5NH3+) and chloride ion (Cl-), which combine to form the ethylammonium chloride salt.
Conclusion :

Ethylammonium chloride salt is formed when ethylamine reacts with one mole of HCl.

Based on inductive effect, solvation effect, and steric hindrance of the alkyl group in aqueous medium the basic strength order of the amines is:
(C2H5)2NH > (C2H5)3N > C2H5NH₂ > NH3

More is the substitution in amine, more is +I effect hence more will be the basic strength. The correct order of basic strength: 3° > 2° > 1°
In the gas phase, where intermolecular forces such as hydrogen bonding do not play a significant role, the basicity of amines is primarily determined by the availability of the lone pair of electrons on the nitrogen atom for bonding with a proton (H+), and by the effect of alkyl groups that can donate electron density to the nitrogen atom, increasing its basicity.
Primary (1°) amines have one alkyl group attached to the nitrogen atom, secondary (2°) amines have two, and tertiary (3°) amines have three. Alkyl groups are electron-donating groups that increase the electron density on the nitrogen atom, making it more basic by enhancing its ability to donate the lone pair of electrons.
Therefore, in the gas phase, without the effects of solvation (like hydrogen bonding in a solvent), the order of basicity is determined by the inductive effect of the alkyl groups. More alkyl groups means a stronger inductive effect, which increases the basicity. The correct order of basicity in the gas phase is:
3° > 2° > 1°

The pKb value is an indicator of the basicity of a substance in water; lower pKb values indicate stronger bases, while higher pKb values indicate weaker bases. The basic strength of an amine in water is influenced by factors such as the electron-donating or withdrawing nature of substituents and the ability of the compound to stabilize the conjugate acid formed upon accepting a proton.
C₂H₅NH₂ (ethylamine) is a primary aliphatic amine and is relatively basic due to the electron-donating effect of the ethyl group, increasing the electron density on the nitrogen atom.
C₆H₅NHCH₃ (N-methylaniline) is a secondary amine where the nitrogen is attached to an aromatic ring (phenyl group) and a methyl group. The phenyl group is electron-withdrawing by resonance, reducing the electron density on the nitrogen atom, making it less basic compared to aliphatic amines.
(C₂H₅)₂NH (diethylamine) is a secondary amine with two ethyl groups. It is more basic than primary amines due to the increased electron-donating inductive effect of the two alkyl groups.
C₆H₅NH₂ (aniline) is a primary aromatic amine. The lone pair of electrons on the nitrogen atom is delocalized into the aromatic ring, significantly reducing its availability to bond with a proton. This makes aniline much less basic than aliphatic amines.
The higher is the value of pK_b, weaker is the basic strength. Lone pair of electron of nitrogen in amine (aniline) is involved in delocalization and hence its availability for protonation is minimum. It is least basic among the given options hence its pK_b is highest.

More the basic nature of amine, more will be the K_b value.
Basic nature

(C₂H₅)₂NH > C₂H₅NH₂ > CH₃NH₂ > C₆H₅N(CH₃)₂
Kb : 10^–3 10^–3.29 10^–3.38 10^–8.92

The correct answer is novestrol.

• Novestrol is also known as ethinylestradiol.
  • It is an antifertility drug that is commonly used in combination with progestin in birth control pills.
  • It is also sometimes used for the diagnosis of menopause as a part of menopausal hormone therapy.
  • The primary function of novestrol is stopping egg ovulation during the menstrual cycle.

Additional Information

• Aspartame is an artificial non-saccharide sweetener.
  • It is about 200 times sweeter than sucrose.
• Soframycin is a skin cream that contains Framycetin.
  • It is an antibiotic medicine.
  • It is used for the treatment of various skin conditions caused by or suspected to have a bacterial infection.
• Prontosil is an antibacterial drug of the sulfonamide group.
  • It has a relatively broad effect against gram-positive cocci but not against enterobacteria.
  • It is one of the earliest antimicrobial drugs and was widely used in the mid-20th century but is little used today because better options now exist.

The formula of ethyl alcohol is C₂H₅OH
In the option, it is given as C₂H₃OH

Correct answer: 1)

Concept:

• The amino group has a negative inductive effect (electron-withdrawing property).
• It causes the alpha carboxyl group carboxylate ion to become more stable due to the delocalization of electrons on the conjugate base.
• It increases the acidity of the alpha-carboxyl group.

Explanation:

• Amino acids are organic compounds containing an amino group and an acidic group as substitutes for alpha carbon.
• In amino acetic acid, the NH₂​ group is electron-repelling in nature.
• Thus it reduces the tendency to release proton from the Aminoacetic acid.

Conclusion:

Thus, option 1 is correct. If both assertion and reason are true and the reason is the correct explanation of the assertion.

Crystal lattice -The crystal lattice is a symmetrical 3-dimensional arrangement of constituent particles (atoms, ions, or molecules) inside a crystalline solid as points.

• In other words, a crystal lattice is made up of a very large number of unit cells where every lattice point is occupied by one constituent particle (atom, ion, or molecule).

Lattice Point - In a crystal lattice, each atom, ion, or molecule is represented by a single point which is known as a lattice point.​

Unit Cell- It is the smallest part of a crystal lattice.

• It is the simplest repeating unit in a crystal structure.

​Types of unit cell -

1) Primitive Unit Cell - In this unit cell, the constituent particles only occupy the corner position.

2) Centered Unit Cell-

• Body-Centered Unit Cell - In this unit cell, the constituent particle is present at all corners and at the center of the unit cell.
• Face-Centered Unit Cell - In this unit cell, the constituent particles are present at the corners and at the center of all the faces of the unit cell.

Explanation:
Packing Efficiency- The packing efficiency is the percentage of total space filled by the particles.

• The fraction of total space filled is known as the packing fraction.
• Packing efficiency = Volume occupied by spheres × 100 / Total volume of a cube
• OR Packing efficiency = No. of lattice points in unit cell × volume occupied by one lattice point × 100 / Total volume of a cube

​In Simple cubic lattice:

• The volume occupied by one sphere = 4/3π r³
• Let the edge length of a cube be 'a' and the radius of each particle be 'r'
• a= 2r
• The volume of the cube = a³ = (8r)³
• Packing efficiency of Simple cubic lattice = 52.4%

​In Body-Centered Cubic lattice:

• No. of lattice points in BCC lattice = 2
• The volume occupied by spheres = 2 ×  π r³
• Let the edge length of a cube be 'a' and the radius of each particle be 'r'
• a =
• The volume of the cube = a3
• Packing efficiency of Body-Centered Cubic lattice = 68.04%

​In Cubic- Closed lattice:

• No. of lattice points in FCC lattice = 4
• The volume occupied by spheres = 4 ×  π r3
• Let the edge length of a cube be 'a' and the radius of each particle be 'r'
• a =
• The volume of the cube = a3
• Packing efficiency of Face-Centered Cubic lattice = 74%

Therefore, the packing efficiency in Simple cubic lattice = 52.4% , Body-Centered Cubic lattice = 68.04%, Face-Centered Cubic lattice = 74%

π r3​In Simple cubic lat43πr

Face-centred Cubic Unit Cell:-

• An FCC unit cell has atoms at all four corners of the crystal lattice, as well as in the centre of each of the cube's faces.
• Only 1/2 of each atom belongs to an individual cell, and the atom present at the face-centred is shared by two adjacent unit cells.
• A face-centred cubic unit cell structure is made up of atoms arranged in a cube with a fraction of an atom in each corner and six additional whole atoms in the centre of each cube face.
• Eight other unit cells share the atoms in the corner of the cube.
• The packing efficiency of FCC lattice is 74%.

Calculation:-

Atom (A) occupies the corner locations in a face-centred cubic lattice.

Each of the eight corner places provides one-eighth of the unit cell. As a result, the total number of (A) atoms per unit cell is calculated.

Total atoms at the corners = 1 / 8 × 8 = 1.

The face centre positions were held by Atom (B).

There are six different face centre positions to choose from.

One of the face-centred points is missing an atom of (B).

As a result, there are five face centre slots that are occupied (B).

Each of these positions adds one-half to the unit cell. As a result, the total number of (B) atoms per unit cell is calculated.

Total atoms at the faces = 1/ 2 × 5 = 2.5.

Thus, the formula will be AB_2.5 = A₂B₅.

To obtain a stable emulsion, sometimes, small quantities of certain other substances are added during its preparation. The substances thus added to stabilize the emulsions are called emulsifiers or emulsifying agents.

Adsorption is the process which involves the accumulation of the molecules of a substance in higher concentration on the surface of a solid or a liquid. For example, gasses are adsorbed on the surface of charcoal.

Physisorption occurs due to Van der Waals forces. On increasing the temperature, the adsorbate can split into atoms and form chemical bonds with the adsorbent and hence, cause chemisorption.

Chemisorption is stronger than physisorption. Chemisorption involves the forming of a chemical bond between the adsorbent and the adsorbate whereas in physisorption, the molecules are held together by weak Van der Waal’s forces. Therefore, chemisorption is stronger.

Chemisorption is a kind of adsorption that involves a chemical reaction between the adsorbent and adsorbate, resulting in the formation of a chemical bond between the two. Since a bond is to be formed, chemisorption is highly dependent on the reactants(adsorbate and adsorbent) and has a large heat of adsorption. Also, since it involves bond formation, it cannot be multi-layered. Chemisorption is favoured to occur at high temperature.

Sorption refers to the process where adsorption and absorption occur at the same time. Cotton dipped in ink is one of the cases where both adsorption and absorption, that is, sorption occurs.

Physisorption is reversible as the molecules of the adsorbate are held to the adsorbent by weak Van der Waals forces which can be broken easily. Physisorption is exothermic and so, ΔH is negative. Adsorption is a spontaneous process. In adsorption, the movement of the adsorbed molecule is restricted. As a result the entropy change (ΔS) is negative.

Physisorption is an exothermic process. According to Le-Chatelier’s principle, an exothermic reaction is favoured by a decrease in temperature. Therefore, the extent of physisorption decreases on increasing temperature.

In physical adsorption, the molecules of the adsorbate stick to the surface of the adsorbent due to very weak forces which is known as Van der Waals force. Van der Waals force is similar to the forces that cause condensation of gas into liquid.

Given,
k = 3.28 × 10^-4 s^-1
The general formula to find the units for rate constant, k = (mol L^-1)^1-ns^-1 where n is the order of the reaction. The value of n must be 1 for (mol L^-1)^1-ns^-1 to become s^-1.
Therefore,k = 3.28 × 10^-4s^-1 represents a first order reaction.

Given, R=0.6 s^-1 and k= 0.035
For a first order reaction R= k [A]

Acid hydrolysis of ester, CH₃COOC₂H₅ + H₂O → CH₃COOH + C₂H₅OH
The order of the reaction may be altered sometimes by taking reactant in excess compared to the other.
The rate law R= k [CH₃COOC₂H₅] [H₂O] however water is present in excess.
So, R= k [CH₃COOC₂H₅].

Given,
[A] = 0.75 M, k= 0.02
The reaction belongs to pseudo first order reaction so, the unit is s^-1
R= k [A]= 0.02 × 0.75= 0.015 s^-1.

Given, [A] = 0.5 M, [B] = 0.1 M and k= 0.03
From the rate law it is evident that the order of the reaction is 1+ 0.5 = 1.5 = 32
Therefore the unit of k= (mol L^-1)^1-1.5 s^-1 = (L/mol)^1/2 s^-1
R= k[A]¹[B]^1/2 = 0.03 × 0.5 × 0.1^1/2 = 4.74 × 10^-2(L/mol)^1/2 s^-1.

Since it is an elementary reaction, its rate law r₁= k [A] ³[B]
When the concentrations are changed the new rate will be r₂= k (2[A])³([B]/2) = 4k[A]³[B]
So, r₂ = 4r₁.

Fractional order reactions are reaction whose order is a fraction. This reaction is an example of fractional order reaction, where the order of the reaction is 5/2.
The rate law for the reaction is known to be R= [C₂H₄] [I₂]3/2.

Rusting of iron is one of the most common forms of corrosion. To prevent iron from rusting, generally, more active metals are coated on it. The metal which is often used for coating iron is zinc (which is more active) and this process is called galvanization.

Galvanization is the process of coating iron with zinc to prevent its oxidation. Anti-rust solutions are alkaline phosphate and alkaline chromate solutions. The alkalinity prevents the availability of hydrogen ions. Cathodic protection is the process of connecting the iron object to be protected to a more active metal either directly or through a wire.

Rust is a general term for a series of iron oxides, usually, reddish-brown oxides, formed by the reaction of iron with oxygen in the presence of water or moisture. Water is usually present in the form of water vapour and oxygen is always present in the normal atmosphere. The oxygen needs moisture as a catalyst and reactant to accelerate the reaction, so in the absence of moisture, iron won’t rust.