Chemistry

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Boron is the only non-metallic and extremely hard element in group 13, and it is also used to make bulletproof vests. Boron exists in a variety of allotropic forms. It usually has a high melting point and no d orbital. Using 2s and 2p orbitals, it can achieve a maximum covalency of 4 . Because the octet of boron is not completed in trivalent halides of boron, it acts as Lewis acid. It forms an adduct when it reacts with Lewis base.

BF₃+NH₃→H₃N−B−F₃

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B₂H₆ + 2NMe₃→ 2BH₃NMe₃   BH₃NMe₃+H₂O → H₃BO₃ + NMe₃ + 6H₂

(A)                        (B)                                            (C)

(A): B₂H₆

(B): 2BH₃NMe₃

(C): H₃BO₃

This is a Long Answers Type Questions as classified in NCERT Exemplar

(i) Organosilicon polymers having (R₂SiO₂) as monomer units are called silicones. Silicones contain organic side groups which surround it giving alkane like nature and makes it hydrophobic. Silicones are applicative in electrical insulators, water proofing, sealant. They have been utilized in the biological field in cosmetic implants and other surgeries.

(ii) Boranes correspond to alkane-like compounds of boron. They consist of boron and hydrogen. Most common borane existing is dibecane.

4BF₃ + 3LiAlH₄?2B₂H₆ + 3LiF + 3AIF₃

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Both the compounds, BCl₃ and AlCl₃ are electron deficient compounds. In BCl₃, boron is smaller in size and cannot assemble four big chlorine atoms near it causing steric hindrance and making it unstable.

Hence, BCl₃ exists as a monomer only.

In AlCl₃, aluminum has 3p-orbitals through which chlorine atoms can be accommodated easily to complete its octet and dimer is formed.

(i)  TlCl is more stable than TlCl₃, due to inert pair effect, +1 oxile. oxidation state.

(ii) AlCl3, Al³⁺ is more stable than aluminum ions in +1 state.

(iii) Due to the inert pair effect, +1 oxidation state is more stable than the +3 oxidation state. So, InCl is more stable than InCl_3.

(iv) Boranes correspond to alkane-like compounds of boron. They consist of boron and hydrogen. Most common borane existing is dibecane.

_{4BF3 + 3LiAlH4?2B2H6 + 3LiF + 3AIF3}

This is a Long Answers Type Questions as classified in NCERT Exemplar

When aqueous solution of borax is acidified with hydrochloric acid, boric acid is produced. As the name says, boric acid is acidic in nature but weak acid. Unlike protonic acid, boric acid is monobasic acid. It accepts electrons from the hydroxyl group of water and forms [B (OH)₄]^-.

This is a Long Answers Type Questions as classified in NCERT Exemplar

When aqueous solution of borax is acidified with hydrochloric acid, boric acid is produced. As the name says, boric acid is acidic in nature but weak acid. Unlike protonic acid, boric acid is monobasic acid. It accepts electrons from the hydroxyl group of water and forms [B (OH)₄]^-.

This is a assertion and reason type question as classified in NCERT Exemplar

(A) Explanation:

Alkaline earth metals are stable at room temperature except beryllium carbonate. It decomposes to give beryllium oxide and carbon dioxide. It is kept in an atmosphere of carbon dioxide so that equilibrium shifts to the right. The reaction is shown below. BeCO₃ → BeO+CO₂

This is a assertion and reason type question as classified in NCERT Exemplar

(A) Lithium beimg small in size, polarises large carbonate ion. Polarisation is the distortion of electron cloud of the anion by the cation. Thus, the carbonate of lithium decomposes easily on heating to form lithium oxide and CO₂. The reaction is shown below.

Li₂CO₃ → Li₂O+CO₂