JEE Main Chemistry Mock Test- 5 - JEE MCQ

1-Phenylethanol can be synthesised through the Grignard reaction, which involves the reaction of benzaldehyde with a suitable organomagnesium reagent. The most effective reagent for this purpose is methyl iodide combined with magnesium.

• Benzaldehyde reacts with methyl iodide in the presence of magnesium.
• This reaction forms a new carbon-carbon bond, resulting in the production of 1-phenylethanol.
• The use of Grignard reagents is crucial as they are highly reactive and facilitate this transformation.

Other reagents such as ethyl iodide or methyl bromide are less suitable for this specific reaction. In summary, the combination of methyl iodide and magnesium is the correct choice for effectively preparing 1-phenylethanol from benzaldehyde.

Lucas reagent is a chemical reagent used to classify and identify alcohols based on their reactivity with zinc chloride and hydrochloric acid.

• Concentration: The Lucas reagent must be concentrated for effectiveness.
• Components: It typically consists of hydrochloric acid (HCl) and zinc chloride (ZnCl₂).
• Formulation: The reagent can be prepared with either anhydrous or hydrous zinc chloride.

In this context, the reagent options include:

• Concentrated HCl and anhydrous ZnCl₂
• Concentrated HNO₃ and hydrous ZnCl₂
• Concentrated HCl and hydrous ZnCl₂
• Concentrated HNO₃ and anhydrous ZnCl₂

The correct formulation for the Lucas reagent is the combination of conc. HCl and anhydrous ZnCl₂.

According to the Aufbau principle, the correct order of electron filling in atomic orbitals is important for understanding electron configuration.

• The Aufbau principle states that electrons fill orbitals starting from the lowest energy level to the highest.
• In the provided options, we need to identify the correct sequence of filling orbitals.
• The correct order of energy levels is:
• 1s (lowest energy level)
• 2s
• 2p
• 3s
• 3p
• 4s
• 3d
• 4p
• 5s
• 4d
• 5p
• 5d
• From the options provided, the sequence 1s < 2p < 4s < 3d is accurate.

This sequence reflects the correct filling order based on energy levels, making it essential for predicting the arrangement of electrons in an atom.

Polarity in molecules is determined by the distribution of electrical charge. In simple terms, a molecule is polar if it has a positive end and a negative end, leading to an uneven distribution of charge.

The least polar molecule among the given options is Cl₂. Here’s why:

• Cl₂ (Chlorine gas) is a diatomic molecule made of two identical atoms, which means the charge is evenly distributed, resulting in no dipole moment.
• HCl (Hydrochloric acid) and HBr (Hydrobromic acid) both have significant differences in electronegativity between hydrogen and chlorine or bromine, making them polar.
• BrCl (Bromine monochloride) is also polar due to the difference in electronegativity between bromine and chlorine.

In summary, since Cl₂ has no polar character due to its identical atoms, it is the least polar molecule compared to the others listed.

The ground state electron configuration of a Chromium (Cr) atom, which has an atomic number of 24, can be understood by examining the distribution of its electrons among different energy levels and subshells.

In this configuration:

• Electrons are arranged according to the principle quantum number (n), starting from the lowest energy level.
• The azimuthal quantum number (l) defines the shape of the orbital. For this case:
• l = 1 corresponds to the p orbitals.
• l = 2 corresponds to the d orbitals.

For Chromium:

• The total number of electrons with l = 1 (p orbitals) is 12.
• The total number of electrons with l = 2 (d orbitals) is 5.

Thus, the correct counts for the azimuthal quantum numbers are:

• 12 electrons in p orbitals (l = 1).
• 5 electrons in d orbitals (l = 2).

The +I effect, or positive inductive effect, refers to the ability of alkyl groups to donate electron density through sigma bonds. This effect stabilises positive charges in a molecule. In evaluating which alkyl group has the maximum +I effect, we can consider the structure of each option:

• CH₃ - (Methyl group): This group has a limited +I effect due to its small size and fewer carbon atoms.
• CH₃CH₂ - (Ethyl group): This group has a stronger +I effect than the methyl group, as it has one more carbon atom to donate electron density.
• (CH₃)₂CH - (Isopropyl group): This group has an even greater +I effect due to the presence of two methyl groups, enhancing its ability to donate electrons.
• (CH₃)₃C - (Tert-butyl group): This group exhibits the strongest +I effect among the options. The three methyl groups significantly increase its electron-donating ability.

In summary, the tert-butyl group (CH₃)₃C - demonstrates the maximum +I effect due to its three methyl groups, which effectively stabilise positive charges and enhance electron donation.

Electrovalency refers to the tendency of atoms to form ionic bonds by transferring electrons. Several factors influence this tendency:

• Charge on Ions: A low charge on ions does not favour electrovalency. Higher charges enhance the attraction between ions, promoting ionic bond formation.
• Size of Ions: The size of cations and anions affects electrovalency. A large cation and a small anion can favour electrovalency, while a small cation and a large anion do not.

Thus, the configuration of ions, particularly their charge and size, plays a crucial role in determining the strength and likelihood of ionic bond formation.

Alkyl groups are considered o- and p-directing due to their electronic effects. These effects can be summarised as follows:

• Inductive Effect: Alkyl groups are electron-donating through the sigma bond. This effect decreases with distance but helps to stabilise positive charges and increases electron density on the aromatic ring.
• Mesomeric Effect: Alkyl groups can donate electron density through resonance. This stabilisation of the ring's electron system makes it more reactive towards electrophiles, particularly at the ortho (o) and para (p) positions.
• Hyperconjugation Effect: The overlap of the sigma bond electrons from the alkyl group with the pi system of the aromatic ring enhances the stability of the o- and p- positions, making them more favourable for substitution reactions.

In summary, the directing effects of alkyl groups in electrophilic aromatic substitution reactions arise mainly from their ability to donate electron density, stabilising the intermediate formed during the reaction.

Glucose reacts with acetic anhydride to produce different types of acetates, which are derivatives formed by the addition of acetic acid. The specific product depends on the number of acetate groups attached to the glucose molecule.

• The reaction can yield a monoacetate, where one acetate group is added.
• A tetra-acetate results from the addition of four acetate groups.
• A penta-acetate forms when five acetate groups are attached.
• The final product, a hexa-acetate, occurs when all six hydroxyl groups of glucose are replaced by acetate groups.

In this case, the correct answer is the formation of the penta-acetate, which indicates that five acetate groups have reacted with glucose.

Geometrical isomerism occurs when compounds have the same molecular formula but differ in the spatial arrangement of their atoms. This phenomenon is particularly common in alkenes where double bonds restrict rotation.

• But-1-ene: Does not exhibit geometrical isomerism as it has no substituents on the double bond.
• But-2-ene: Exhibits geometrical isomerism. It can exist in two forms:
  • cis form: Both substituents are on the same side of the double bond.
  • trans form: Substituents are on opposite sides.
• Propene: Lacks geometrical isomerism due to its simple structure with no different substituents on the double bond.
• 1,1-Dichlorobutane: Does not show geometrical isomerism as both chlorine atoms are attached to the same carbon, limiting spatial variation.

In summary, only But-2-ene displays geometrical isomerism due to its ability to form distinct cis and trans configurations.

The coordination number of a metal in coordination compounds refers to the number of ligands bonded to the central metal atom. This number is crucial for understanding the structure and properties of the compound.

• The coordination number is primarily determined by the valency of the metal.
• It is also influenced by factors such as the size of the metal ion and the nature of the ligands.
• In many cases, the coordination number corresponds to the secondary valency of the metal.
• The most common coordination numbers are 4 and 6, but other numbers can occur depending on the metal and ligands involved.

Understanding coordination numbers helps predict the geometry of the compound, which can be tetrahedral, octahedral, or other shapes. This knowledge is essential in fields such as coordination chemistry, as it affects the reactivity and stability of the compounds.

The third ionisation enthalpy is the energy required to remove the third electron from an atom. This property is influenced by several factors, including the electronic configuration and the stability of the resulting ion.

• Iron (Z=26): Iron has a stable electronic configuration, leading to a relatively moderate ionisation enthalpy.
• Chromium (Z=24): Chromium's unique configuration, which includes a half-filled d-subshell, makes it somewhat stable, resulting in a higher ionisation energy than iron.
• Vanadium (Z=23): Vanadium has a less stable configuration compared to chromium, hence its third ionisation enthalpy is lower.
• Manganese (Z=25): Manganese also has a half-filled d-subshell, contributing to a higher stability, which increases its third ionisation enthalpy.

Among these elements, manganese is expected to have the highest third ionisation enthalpy due to its stable electron configuration, which provides significant energy requirements to remove an additional electron.

Planar molecules are those that lie in a single plane. Understanding the geometry of these molecules is essential in chemistry. Here are some key points regarding the characteristics of planar molecules:

• Geometry: Planar molecules typically have a geometry that allows for all atoms to be in the same flat plane.
• Bond Angles: The bond angles in planar molecules are usually 120 degrees, which is common in trigonal planar structures.
• Examples: Certain molecules, like XeF₄, exhibit this planar characteristic due to their specific arrangements of atoms and lone pairs.
• Lone Pairs: The presence of lone pairs can influence the molecular geometry, affecting whether a molecule is planar or not.

In conclusion, identifying whether a molecule is planar involves examining its molecular structure and the arrangement of its atoms and bonds.

To calculate the pH of a decinormal solution of acetic acid (CH₃COOH) that is ionised to 1.3%, follow these steps:

• Determine the concentration of acetic acid: In this case, it is 0.1 M (decinormal).
• Calculate the concentration of ionised acetic acid:
• Ionisation percentage is 1.3%.
• Ionised concentration: 0.1 M × 0.013 = 0.0013 M.
• Use the formula for pH:
• pH = -log[H⁺]
• Substituting the ionised concentration: pH = -log(0.0013).
• Given that log(1.3) = 0.11, we can find:
• log(0.0013) = log(1.3) - 3 (since 0.0013 = 1.3 × 10^-3).
• This gives us: log(0.0013) = 0.11 - 3 = -2.89.
• Finally, calculate the pH:
• pH = -(-2.89) = 2.89.

The pH of the solution is therefore 2.89.

Sodium nitroprusside interacts with the sulphide ion, resulting in a purple colour. This colour change is due to the formation of a specific complex. The key product formed is:

• [ Fe(CN)₅ NOS ]^4-

This complex is characterised by the presence of:

• Iron (Fe) at its core
• A combination of cyanide (CN) ligands
• The nitrosyl group (NOS) which contributes to the purple colour

The formation of this complex occurs when sodium nitroprusside reacts with the sulphide ions, leading to a notable visual change that can be observed in chemical analyses.

Isomers are compounds that share the same molecular formula but have different structural arrangements. Here are some examples of isomers:

• Ethyl alcohol (ethanol) and dimethyl ether have the same formula (C2H6O) but differ in structure and properties.
• Acetone and acetaldehyde both contain three carbon atoms but differ in functional groups and reactivity.
• Propanoic acid and propanone are both C3H6O compounds; however, their functional groups lead to different characteristics.
• Methyl alcohol (methanol) and dimethyl ether share the same molecular formula but have different arrangements of atoms.

Understanding isomers is crucial in chemistry as they can exhibit vastly different behaviours despite having the same chemical composition.

The process of chlorinating toluene with an excess of chlorine in the presence of light and heat produces several products. After this step, treatment with aqueous NaOH leads to specific outcomes. Here’s a simplified breakdown of the reaction products:

• o-cresol: This compound is formed as one of the possible products.
• p-cresol: Another isomer resulting from the chlorination process.
• 2, 4-Dihydroxytoluene: This compound may also be produced during the reaction.
• Benzoic acid: The final product of interest, particularly after the treatment with NaOH.

Among these, the key product resulting from the reaction sequence is benzoic acid, which is a significant organic compound used in various applications, including as a food preservative and in the synthesis of other chemicals.

To calculate the weight average molecular weight of the polymer, follow these steps:

• Identify the molecular weights and their corresponding percentages:
  • 20,000 g/mol - 30% of molecules
  • 30,000 g/mol - 40% of molecules
  • 60,000 g/mol - 30% of molecules
• Calculate the contribution of each molecular weight to the total weight:
• For 20,000 g/mol: 20,000 g/mol × 0.30 = 6,000
• For 30,000 g/mol: 30,000 g/mol × 0.40 = 12,000
• For 60,000 g/mol: 60,000 g/mol × 0.30 = 18,000
• Add the contributions together to get the total weight: 6,000 + 12,000 + 18,000 = 36,000

The final step is to determine the weight average molecular weight by dividing the total weight by the total percentage (which is 1 or 100%). Therefore, the weight average molecular weight of the polymer is 36,000 g/mol.

The process of electrolysis involves breaking down a compound using electricity. When sodium chloride (NaCl) is melted and subjected to electrolysis, the following key products are formed:

• Sodium (Na): This element is produced at the negative electrode (cathode) due to the reduction of sodium ions.
• Chlorine (Cl₂): This diatomic molecule is released at the positive electrode (anode) through the oxidation of chloride ions.

During this process:

• The sodium ions gain electrons, transforming into neutral sodium metal.
• The chloride ions lose electrons, forming chlorine gas.

It is important to note that:

• Electrolysis of molten sodium chloride does not produce hydrogen (H₂) or oxygen (O₂).
• Instead, the primary products are sodium and chlorine.

In summary, the correct products of the electrolysis of molten sodium chloride are:

• Sodium (Na)
• Chlorine (Cl₂)

In an acidic medium, the dichromate ion plays a crucial role in the oxidation of ferrous ions to ferric ions. To understand the gram equivalent weight of potassium dichromate, we can break it down as follows:

• The gram molecular weight of potassium dichromate is 294 grams.
• To find the gram equivalent weight, we need to consider the number of electrons transferred in the reaction. In this case, the dichromate ion can accept 6 electrons when it reduces to chromium(III).
• The formula for calculating gram equivalent weight is:
• Gram Equivalent Weight = Gram Molecular Weight / n
• Where n is the number of electrons transferred. Here, n = 6.
• Thus, the calculation is:
• Gram Equivalent Weight = 294 grams / 6 = 49 grams

Therefore, the gram equivalent weight of potassium dichromate is 49 grams.

The total number of unpaired electrons in the following complexes is calculated as follows:

• [CoCl₆]⁢3: Cobalt has an oxidation state of +3. Its electronic configuration is [Ar] 3d⁶. In this complex, all six chloride ions are weak field ligands, leading to high spin configuration. This results in 4 unpaired electrons.
• [Cr(NH₃)₆]⁢3: Chromium in this complex has an oxidation state of +3, with the configuration [Ar] 3d³. The ammonia ligands are strong field ligands, causing pairing of electrons. This gives 3 unpaired electrons.
• [Zn(NH₃)₄]⁢2: Zinc has an oxidation state of +2 and an electronic configuration of [Ar] 3d¹⁰. As all d-orbitals are fully filled, there are no unpaired electrons here.

Summing the unpaired electrons from each complex:

• 4 (from [CoCl₆]⁢3)
• 3 (from [Cr(NH₃)₆]⁢3)
• 0 (from [Zn(NH₃)₄]⁢2)

This results in a total of 7 unpaired electrons.

The sum of ions in an aqueous solution of CrCl₃.5NH₃ and CrCl₃.4NH₃ can be calculated as follows:

• Each CrCl₃ compound dissociates into:
• 1 Cr³⁺ ion
• 3 Cl^- ions
• For CrCl₃.5NH₃:
• It produces 4 ions: 1 Cr³⁺ + 3 Cl^-
• For CrCl₃.4NH₃:
• It also produces 4 ions: 1 Cr³⁺ + 3 Cl^-
• Combining both solutions:
• 4 ions from CrCl₃.5NH₃
• 4 ions from CrCl₃.4NH₃
• Total ions: 4 + 4 = 8 ions.

Therefore, the total number of ions present in the solution is 8.

To identify planner species among the given compounds:

• SF₂ – This species is not a planner molecule due to its bent shape.
• SF₄ – This compound has a seesaw geometry, which is not planner.
• SF₆ – With an octahedral structure, this molecule is also not planner.
• SO₂ – This species is bent and thus is a planner molecule.
• SO₃ – Exhibiting trigonal planar geometry, this molecule is planner as well.

In summary, the planner species identified from the list are SO₂ and SO₃.

Isomeric amines with the molecular formula C₄H₁₁N can be identified based on their structural variations. Here are the key points regarding the isomers:

• Isomeric amines are compounds that share the same molecular formula but differ in their structure.
• For the formula C₄H₁₁N, there are a total of 8 distinct isomeric amines.
• These isomers can include:
• Primary amines (where the nitrogen atom is attached to one carbon chain).
• Secondary amines (where the nitrogen atom is bonded to two carbon chains).
• Tertiary amines (where the nitrogen atom is connected to three carbon chains).
• The variations arise from different arrangements of the carbon skeleton and the position of the amine group.

Understanding these isomers is important in organic chemistry, as they can exhibit different chemical properties despite having the same molecular formula.