Chemistry: CUET Mock Test - 5 - CUET MCQ

Alcohols undergo dehydration in the presence of protic acids to form either alkenes or ethers depending upon the reaction temperature conditions. At 413K, ethanol forms an ether with H₂SO₄.

In ion, Br has sp3 hybridisation

In XeO3, Xe has sp³ hybridisation.

Outer electron configuration of Ti = 3d²4s²
So, Maximum O.S. of Ti = +4
Outer E.C. of V = 3d³4s²
So, Maximum O.S. of V = +5 Outer E.C. of Mn = 3d⁵4s²
So, Maximum O.S. of Mn = +7
Outer E.C. of Cu = 3d¹⁰4s¹
So, Maximum O.S. of Cu = +2
So, correct option is : A-II, B-III, C-I, D-IV

Cu has positive value in 3d series.

In the first transition series, the standard electrode potential ((E0M2+/M) indicates the ease with which a metal can be reduced to its metallic form from its ion in aqueous solution. A positive value for (E⁰_M²⁺/M) means that the reduction process is favorable, and the metal is relatively less reactive compared to those with negative values.

Among the given options:

Chromium (Cr) has a negative standard reduction potential.
Vanadium (V) also has a negative value.
Copper (Cu) has a positive standard reduction potential ((E⁰_Cu²⁺/Cu = +0.34 V)), meaning it is readily reduced to its metallic state.
Nickel (Ni) has a negative standard reduction potential.

= 0.34 V

= –0.90 V

= –1.18 V

= = –0.25 V

The magnetic moment of a divalent ion in an aqueous solution depends on its electronic configuration, which in turn is determined by the element's atomic number.

Atomic number (z = 25) belongs to Mn atom

E.C. of Mn = [Ar]3d⁵4s²

E.C. of Mn²⁺ ion = [Ar]3d⁵4s⁰

Number of unpaired electrons = 5

μ = 5.92 BM

Scandium (Sc) is a transition metal element that belongs to the 3rd period of the periodic table, and it has only one oxidation state, +3.

The colour of a transition metal ion is due to the presence of partially filled d orbitals, which can absorb certain wavelengths of visible light and reflect others, giving the ion its characteristic colour.

However, Scandium ion (Sc³⁺) does not have any partially filled d orbitals, as it has lost all three of its valence electrons to form the 3+ oxidation state. As a result, Sc³⁺ does not absorb any visible light and therefore appears colourless.

On the other hand, the other transition metal ions listed in the options all have partially filled d orbitals and exhibit characteristic colours in aqueous solutions or as solid compounds.

For example, V²⁺ (Vanadium ion) is blue-green, Mn²⁺ (Manganese ion) is pale pink, and Co³⁺ (Cobalt ion) is yellow.

Therefore, the correct answer is Option 1, Sc³⁺ (Scandium ion), which is the only colourless transition metal ion among the options given.

In general species having no unpaired electron is colourless. So Sc3+ has electronic configuration [Ar] 3d⁰4s⁰

So, it is colourless ion.

Concept:

The spin only magnetic moment (μ) in (BM),

Where, n = Number of unpaired electrons

The highest value of n in transition metal complex is 5 in its d⁵ configuration.

n = Maximum number of unpaired electrons = 5

B.M is Bohr Magneton

= 5.916 BM

Concept:

Paramagnetic materials:

• Small, positive susceptibility to magnetic fields.
• These materials are slightly attracted by a magnetic field.
• Paramagnetic properties are due to the presence of some unpaired electrons, and from the realignment of the electron paths caused by the external magnetic field
• Paramagnetic materials include magnesium, molybdenum, lithium, and tantalum.

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Magnetic moment:

• The strength of a magnet and its orientation in presence of a magnetic field is called its magnetic moment.
• The complexes have lone electrons in them, unpaired which contribute to the magnetic moment. It is given by the formula:

​

Explanation:

• Chromium belongs to the d block. Its electronic configuration is: [Ar]3d⁵4s¹.
• In the Cr⁺² oxidation state, it loses two electrons and has the configuration [Ar]3d⁴.
• The number of unpaired electrons n = 4.

​

• Hence, the magnetic moment is:

μ = 4.90 BM

Hence, the magnetic moment of Cr²⁺ is 4.90 BM.Additional InformationDiamagnetic materials

• Weak, negative susceptibility to magnetic fields
• Diamagnetic materials are slightly repelled by a magnetic field.
• All the electrons are paired so there is no permanent net magnetic moment per atom.
• Most elements in the periodic table, including copper, silver, and gold, are diamagnetic.

The correct answer is Square planar structure
Coordination Number: The coordination number of the nickel ion (Ni²⁺) in the complex [Ni(CN)₄]^2- is 4. This is because there are four cyanide ions (CN-) surrounding the central metal ion.

Nature of Ligands: Cyanide ions (CN-) are strong-field ligands. In CFT, strong-field ligands typically lead to the pairing of d-electrons and the formation of low-spin complexes.

Electron Configuration of Ni²⁺: The electron configuration of the nickel ion (Ni²⁺) is [Ar] 3d⁸. In the presence of strong-field ligands, the electrons fill the lower-energy orbitals before pairing, leading to a low-spin configuration.

Geometry: In a square planar structure, the ligands approach the central metal ion along the x, y, and z axes, resulting in a flat, square arrangement. This is the favored geometry for low-spin d8 complexes with strong-field ligands.

Conclusion:-

According to CFT, [Ni(CN)₄]^2- is expected to have a square planar structure due to the combination of a coordination number of 4 and the strong-field nature of the cyanide ligands.

T he correct answer is Option 1
Key Points

• Cyclohexane is a cycloalkane with the molecular formula C6H12
• Cyclohexane is a non-polar, colorless flammable liquid with a distinctive detergent-like odor, reminiscent of cleaning products.
• Cyclohexane is mainly used for the industrial production of adipic acid and caprolactam, which are precursors to nylon.
• It is also called Hexanaphthene.
• It is soluble in ether, alcohol, acetone (non-polar solution)

It is immiscible in water.
Structure of Cyclohexane-
Additional Information
Production of Cyclohexane-
Cyclohexane is produced by hydrogenation of benzene in the presence of a Raney nickel. catalyst.

Uses of Cyclohexane-

1. It is used as a solvent.
2. It is frequently used as a recrystallization solvent, as many organic compounds exhibit good solubility in hot cyclohexane and poor solubility at low temperature
3. It is used for the calibration of differential scanning calorimetry.

Important Points

• Cyclohexane is the IUPAC name of C6H12.

By direct halogenation of benzene ring:

if X = Cl then the reaction is as follows:

Symmetrical ethers are formed when alcohols are dehydrated with H₂SO₄ at controlled temperatures. This is an S_N2 reaction involving the attack of alcohol molecule on a protonated alcohol to give ethers.

The reactant sodium ethoxide is a strong nucleophile as well as a strong base, and hence elimination predominates over S_N2 to form alkene as a major product.

Solubility is the maximum amount of solute that can be dissolved in a given solvent at a particular temperature and pressure. It is usually expressed in grams of solute dissolved in 100 grams of the solvent. Any more solute added beyond this forms a supersaturated solution as none of the particles dissolve any more.

Explanation: This is because the (-O-) group in ethers does not contain any active site as compared to for example, hydroxyl group (OH) in alcohols. However, they undergo C-O bond cleavage in drastic conditions.

The C-O bond of the phenol group is stronger than the C-O bond of the ether and alkyl aryl group. This is due to the partial double bond character because of sp² hybridised C-O cond. Therefore, the weaker C-O bond is broken and two major products, viz., phenol and iodomethyl benzene, are formed.

Anisole undergoes Friedel-Crafts acylation where an acyl group is introduced at ortho and para position by reaction with acyl chloride with anhydrous AlCl₃ as catalyst. The para isomer will be the major product.

Anisole undergoes nitration in the presence of concentrated acids H₂SO₄ and HNO₃ to yield a mixture of ortho and para nitroanisoles.

When cumene hydroperoxide is hydrolysed with a solution of dilute acid, it results in the formation of phenol and acetone, of which the latter is obtained in large quantities.

Oleum is a mixture of H₂SO₄ and SO₃ that is added to benzene to form benzene sulphonic acid, which on subsequent treatment as shown, gives phenol.

As the size of the alkyl group becomes larger, it prevents the formation of hydrogen bonds with water molecules and hence the solubility goes on decreasing with the increase in the size or mass of the compound.

Phenol is more acidic than alcohols because of their better stability and resonant structures. The pK_a values of phenol and ethanol are 10 and 15.9 respectively, which when converted to K_a values gives a ratio of about a million.

As the branching in the structure increases, the surface area decreases and hence, the van der Waal forces decrease. This results in the reduction of boiling points of isomeric alcohols from primary to tertiary structures.

Methoxymethane and ethanol are of comparable masses and it can be easily pointed out that ethanol will have a higher boiling point than it because of the presence of intermolecular hydrogen bonding. 455K is very high and is actually the boiling point of phenol.

In an equilibrium system of gas dissolved in solvent, when pressure over it is increased more and more gas particles are forced into a smaller volume. This also increases the rate at which they strike the surface of the solvent to enter it. Consequently, more gas dissolves with increasing pressure. In the case of increasing temperature, gas particles gain sufficient energy to escape the solvent and solubility decreases.

Henry’s law is formulated asp = K_H x X (mole fraction). From this, it is seen that as K_H increases, mole fraction decreases in order to compensate the increase in partial pressure of the gas. Hence, higher the K_H value lower is the solubility. Therefore, argon is less soluble in water than CO₂ at 298 K.

When halobenzene is fused with NaOH at 623K and 320atm with a copper salt as catalyst, sodium phenoxide is produced which on treatment with dilute HCl yields phenol. This is also known as Dow’s process.

Carbolic acid is another name for phenol. Simply warming an aqueous solution of benzene diazonium chloride salt or treating it with a dilute acid, will result in the formation of phenol.

tert-Butyl alcohol is the most heavily branched isomer and is tightly packed compared to the others. This decreases the effective surface area of the alkyl part which is hydrophobic in nature.

FeBr₃, AlCl₃ and BF₃ are Lewis acids, that are required for the substitution in benzene. Phenol has an OH group that activates the aromatic ring and requires the presence of only slightly or non-polar solvents for its halogenation.