Group 13 Elements (Boron Family) MCQ Quiz in मराठी - Objective Question with Answer for Group 13 Elements (Boron Family) - मोफत PDF डाउनलोड करा

Concept:

Diborane (B₂H₆):

Diborane, with the chemical formula B₂H₆, is an electron-deficient compound of boron and hydrogen. It is a colorless, highly reactive gas with a distinctive, unpleasant odor. Diborane is an important compound in the chemistry of boranes and serves as a starting material for many boron compounds.

Properties:

• Formula: B₂H₆

• Molecular weight: 27.67 g/mol

• Melting point: -164.8 °C (-264.6 °F)

• Boiling point: -92.5 °C (-134.5 °F)

• Density: 0.431 g/cm³ at -95 °C

• Reactivity: Highly reactive and can ignite spontaneously in air

Synthesis:

Diborane can be synthesized by the reaction of boron trifluoride etherate (BF₃) with sodium borohydride (NaBH₄):
4BF₃ + 3NaBH₄ → 2B₂H₆ + 3NaBF₄

Uses:

• Chemical synthesis: Used as a reagent in organic and inorganic chemical synthesis, particularly in hydroboration reactions.

• Rocket propellant: Investigated as a high-energy fuel for rockets and jet engines.

• Doping agent: Used in the semiconductor industry for doping silicon wafers with boron.

Explanation:

The structure of diborane can be explained by looking at the bonding in the molecule:

• Diborane consists of two boron atoms and six hydrogen atoms.

• The molecule has four terminal hydrogen atoms, each forming a normal covalent bond with a boron atom.

• There are two bridging hydrogen atoms that form three-center two-electron bonds (also known as banana bonds) with the two boron atoms.

Structural Representation

The correct representation of diborane (B₂H₆) is given by the structure where two boron atoms are connected through two hydrogen bridges, and each boron atom is additionally bonded to two terminal hydrogen atoms:

Conclusion:

The structure of diborane is essential for understanding its unique bonding properties. The presence of three-center two-electron bonds (bridging hydrogens) is a defining feature of diborane. Thus, the correct representation of Diborane is:

Concept:

Aluminothermy, commonly known as the thermite process, is a type of exothermic oxidation-reduction reaction used in welding, primarily for joining railway tracks and large iron structures. It involves the reaction of aluminium powder with metal oxides.

Explanation:

1. As compared to iron, aluminium has greater affinity for oxygen: This is correct. In the thermite process, aluminium acts as a reducing agent and reacts with iron oxide to produce molten iron and aluminum oxide.                                                                                                                                                                                                                     The reaction: \(2 \text{Al} + \text{Fe}_2\text{O}_3 \rightarrow 2 \text{Fe} + \text{Al}_2\text{O}_3+Heat \), This reaction is highly exothermic and produces a significant amount of heat, which is why it is used for welding.

2. As compared to aluminium, iron has greater affinity for oxygen: This is incorrect. Aluminium has a greater affinity for oxygen than iron, which is why it can reduce iron oxide in the thermite reaction.

3. Reaction between aluminium and oxygen is endothermic: This is incorrect. The reaction between aluminium and oxygen (as part of the thermite reaction) is exothermic.

4. Reaction between iron and oxygen is endothermic: This is incorrect. The reaction between iron and oxygen can also be exothermic, but this is irrelevant to the thermite process used in welding.

Conclusion:

The correct statement is: As compared to iron, aluminium has greater affinity for oxygen

Concept:

An alloy is a combination of two or more elements, where at least one of the elements is a metal. Alloys are designed to have enhanced properties compared to their constituent elements, such as increased strength, durability, or corrosion resistance.

Explanation:

• An alloy is a mixture of two or more metals: This is a correct statement. Examples include brass (copper and zinc) and bronze (copper and tin).

• An alloy is a mixture of two or more metal and non-metal elements that have metallic properties: This is also a correct statement. An example is steel, which is an alloy of iron with small amounts of carbon (a non-metal).

• An alloy has a fixed composition: This is an incorrect statement. Alloys do not have a fixed composition; the ratio of constituent elements can vary within certain limits to produce different properties. For example, the percentage of carbon in steel can vary to produce different types of steel with varying properties.

• An amalgam is an alloy containing Hg: This is a correct statement. An amalgam is an alloy where mercury is one of the components, often used in dental fillings and other applications.

Conclusion:

The incorrect statement is: An alloy has a fixed composition.

Concept:

Diborane (B₂H₆):

Diborane, with the chemical formula B₂H₆, is an electron-deficient compound of boron and hydrogen. It is a colorless, highly reactive gas with a distinctive, unpleasant odor. Diborane is an important compound in the chemistry of boranes and serves as a starting material for many boron compounds.

Properties:

• Formula: B₂H₆

• Molecular weight: 27.67 g/mol

• Melting point: -164.8 °C (-264.6 °F)

• Boiling point: -92.5 °C (-134.5 °F)

• Density: 0.431 g/cm³ at -95 °C

• Reactivity: Highly reactive and can ignite spontaneously in air

Synthesis:

Diborane can be synthesized by the reaction of boron trifluoride etherate (BF₃) with sodium borohydride (NaBH₄):

4BF₃ + 3NaBH₄ → 2B₂H₆ + 3NaBF₄

Uses:

• Chemical synthesis: Used as a reagent in organic and inorganic chemical synthesis, particularly in hydroboration reactions.

• Rocket propellant: Investigated as a high-energy fuel for rockets and jet engines.

• Doping agent: Used in the semiconductor industry for doping silicon wafers with boron.

Explanation:

In B₂H₆, the boron atoms are bonded to each other and to the hydrogen atoms in a way that involves multi-center bonds:

• No Direct B–B Bond: There is no direct B–B sigma bond in diborane. Instead, the boron atoms are connected through hydrogen bridges.

• Non-Planar Structure: Not all atoms in B₂H₆ lie in a single plane. The structure is three-dimensional due to the bridging hydrogens.

• Normal and Bridge B–H Bonds: Not all B–H bonds are normal covalent bonds. There are four terminal B–H bonds, which are typical covalent bonds, and two bridging B–H–B bonds, which are three-center two-electron (3c-2e) bonds.

Conclusion:

Therefore, the correct statement is: There exists two (three-centre two-electron) bonds between the boron atoms

Concept

When attempting to dehydrate aluminium chloride hexahydrate (AlCl₃·6H₂O) by heating, the behavior of the compound provides insight into its properties and reactions.

Explanation:

• It decomposes completely to give Al₂O₃: This is correct. When AlCl₃·6H₂O is heated, it loses water, and further heating leads to the decomposition of the compound, resulting in the formation of aluminium oxide (Al₂O₃).

• It does not lose water completely: This is not the main reason. Although it may not lose water completely under certain conditions, the primary reason is the decomposition leading to Al₂O₃.

• It undergoes hydrolysis to give Al(OH)₃: While hydrolysis does occur, the decomposition primarily leads to Al₂O₃.

• AlCl₃·6H₂O is very stable: This is not the main reason. The stability of the hydrate itself is not the primary concern in explaining why anhydrous AlCl₃ cannot be obtained.

Conclusion:

The correct reason why anhydrous AlCl₃ cannot be obtained by heating hydrated AlCl₃·6H₂O is: It decomposes completely to give Al₂O₃

Concept:

Aluminothermite Process:

The aluminothermite process, also known as the thermite reaction, is a highly exothermic reaction between aluminum powder and a metal oxide, typically iron(III) oxide (Fe₂O₃). The reaction can be represented by the following chemical equation:

Fe₂O₃ + 2Al → 2Fe + Al₂O₃

This reaction produces aluminum oxide (Al₂O₃) and molten iron (Fe) as products. The process releases a significant amount of heat, allowing the molten iron to reach very high temperatures.

Applications:

• Railroad welding: The thermite reaction is commonly used in welding rail tracks because it provides a portable and effective means to achieve high temperatures and produce molten iron.

• Metal reduction: The process is employed in the production of metals such as chromium, manganese, and titanium, which are difficult to reduce by conventional methods.

• Pyrotechnics: The aluminothermite process is used in pyrotechnic devices for its intense heat and bright flame.

Explanation: 

In the aluminothermite process, aluminium acts as a reducing agent. It donates electrons to the metal oxides, reducing them to their respective metals while aluminium itself gets oxidized to aluminium oxide (Al₂O₃).

The general form of the reaction is:

\(2 \text{Al} + \text{Fe}_2\text{O}_3 \rightarrow 2 \text{Fe} + \text{Al}_2\text{O}_3 \)

Conclusion:

Therefore, In the aluminothermite process, aluminium acts as: A reducing agent

Concept:

Lewis Concept of Acids and Bases
1. Lewis Acid: A Lewis acid is defined as an electron pair acceptor. It is a species that can accept a pair of electrons from another species to form a covalent bond.

• Electron Pair Acceptance: Lewis acids have empty orbitals or are deficient in electron density, making them capable of accepting electron pairs.

2. Lewis Base: A Lewis base is defined as an electron pair donor. It is a species that can donate a pair of electrons to form a covalent bond with a Lewis acid.

• Electron Pair Donation: Lewis bases have lone pairs of electrons available for donation.

Explanation:

Lewis acids are chemical species that can accept an electron pair. Both BCl₃ and AlCl₃ are considered Lewis acids because they have an incomplete octet around the central atom (boron and aluminum, respectively) and can accept electron pairs.

BCl₃ is a stronger Lewis acid than AlCl₃. This is due to the fact that boron is smaller and more electron-deficient than aluminum, which makes it more capable of accepting electron pairs. Additionally, the size and electronegativity of chlorine atoms affect the Lewis acidity:

• Size and Charge Density: Boron has a smaller atomic radius compared to aluminum, leading to higher charge density and a stronger attraction for electron pairs.

• Electron-Withdrawing Effect: Chlorine atoms in BCl₃ effectively withdraw electron density from boron, increasing its Lewis acidity. In AlCl₃, the electron-withdrawing effect is less significant due to the larger size of aluminum.

Conclusion:

Therefore, the correct statement is: BCl₃ and AlCl₃ are both Lewis acids and BCl₃ is stronger than AlCl₃.

Option 3, which states that boric acid accepts OH- from water, is the correct choice to describe why boric acid is an acid.
Explanation:
Boric acid, chemically represented as H3BO3, is a weak acid. It exhibits acidic properties when it comes into contact with water.

1. Bronsted-Lowry Acid-Base Theory:
   The Bronsted-Lowry theory of acids and bases defines an acid as a substance that can donate a proton (H+ ion) and a base as a substance that can accept a proton. In this theory, an acid-base reaction involves the transfer of a proton from the acid to the base.

2. Boric Acid and Water:
   When boric acid (H3BO3) is dissolved in water (H2O), it reacts with water molecules as follows:
   H3BO3 + H2O ⇌ H2BO3- + H3O+

 In this reaction:

• Boric acid, H3BO3, donates a proton (H+) to a water molecule, forming the negatively charged borate ion (H2BO3-) and a hydronium ion (H3O+).
• The water molecule, in this case, acts as a base by accepting the proton.

3. Acceptance of OH- Ion:

•  The formation of the hydronium ion (H3O+) indicates that boric acid has donated a proton (H+) to water. In essence, boric acid has accepted an OH- ion from water, forming H3O+. This is the characteristic behavior of an acid—donating a proton (H+) or accepting an OH- ion in solution.

So, based on the Bronsted-Lowry theory, boric acid is considered an acid because it accepts OH- ions from water, releasing a proton (H+ ion) in the process

Option 3, which states that boric acid accepts OH- from water, is the correct choice to describe why boric acid is an acid.
Explanation:
Boric acid, chemically represented as H3BO3, is a weak acid. It exhibits acidic properties when it comes into contact with water.

1. Bronsted-Lowry Acid-Base Theory:
   The Bronsted-Lowry theory of acids and bases defines an acid as a substance that can donate a proton (H+ ion) and a base as a substance that can accept a proton. In this theory, an acid-base reaction involves the transfer of a proton from the acid to the base.

2. Boric Acid and Water:
   When boric acid (H3BO3) is dissolved in water (H2O), it reacts with water molecules as follows:
   H3BO3 + H2O ⇌ H2BO3- + H3O+

 In this reaction:

• Boric acid, H3BO3, donates a proton (H+) to a water molecule, forming the negatively charged borate ion (H2BO3-) and a hydronium ion (H3O+).
• The water molecule, in this case, acts as a base by accepting the proton.

3. Acceptance of OH- Ion:

•  The formation of the hydronium ion (H3O+) indicates that boric acid has donated a proton (H+) to water. In essence, boric acid has accepted an OH- ion from water, forming H3O+. This is the characteristic behavior of an acid—donating a proton (H+) or accepting an OH- ion in solution.

So, based on the Bronsted-Lowry theory, boric acid is considered an acid because it accepts OH- ions from water, releasing a proton (H+ ion) in the process

Option 3, which states that boric acid accepts OH- from water, is the correct choice to describe why boric acid is an acid.
Explanation:
Boric acid, chemically represented as H3BO3, is a weak acid. It exhibits acidic properties when it comes into contact with water.

1. Bronsted-Lowry Acid-Base Theory:
   The Bronsted-Lowry theory of acids and bases defines an acid as a substance that can donate a proton (H+ ion) and a base as a substance that can accept a proton. In this theory, an acid-base reaction involves the transfer of a proton from the acid to the base.

2. Boric Acid and Water:
   When boric acid (H3BO3) is dissolved in water (H2O), it reacts with water molecules as follows:
   H3BO3 + H2O ⇌ H2BO3- + H3O+

 In this reaction:

• Boric acid, H3BO3, donates a proton (H+) to a water molecule, forming the negatively charged borate ion (H2BO3-) and a hydronium ion (H3O+).
• The water molecule, in this case, acts as a base by accepting the proton.

3. Acceptance of OH- Ion:

•  The formation of the hydronium ion (H3O+) indicates that boric acid has donated a proton (H+) to water. In essence, boric acid has accepted an OH- ion from water, forming H3O+. This is the characteristic behavior of an acid—donating a proton (H+) or accepting an OH- ion in solution.

So, based on the Bronsted-Lowry theory, boric acid is considered an acid because it accepts OH- ions from water, releasing a proton (H+ ion) in the process