Tag: study of boron

Questions Related to study of boron

Which type of bond is present in $[BeF _2] _n$ polymer?

chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

  1. $3C-2e^-$

  2. $3C-4e^-$

  3. $3C-3e^-$

  4. None of these

Show answer
Correct Option: B
Explanation:

$[BeF _2] _n$ contains $3C-4e^-$ bonds.
One $F$ atom and two $Be$ atoms are $3$ centers. The middle $O$ contributes two electrons each to the be atom, thereby a total of $4$ electrons are contributed and it forms $Be−F−Be$ bridges. 

Which is/are correct representation of boranes?

chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

  1. $B _n\, H _{n\, +\, 4}$

  2. $B _n\, H _{n\, +\, 6}$

  3. $B _n\, H _{2n\, +\, 2}$

  4. None of these

Show answer
Correct Option: A,B
Explanation:

The correct representation of boranes include (A) $B _n\, H _{n\, +\, 4}$, called as nido-boranes and (B) $B _n\, H _{n\, +\, 6}$, called as arachno boranes.
(C) $B _n\, H _{2n\, +\, 2}$ is not a correct representation of boranes.
Note: $B _n\, H _{n\, +\, 6}$ are less stable than $B _n\, H _{n\, +\, 4}$

Select the correct statements(s).

chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

  1. $BeCl _2$ tends to dimerize to a 3-coordinate structure in vapor phase, but linear monomer is also known at high temperature.

  2. $BeF _2$ has $3C - 4e^-$ bond.

  3. Bond lengths in all the boron trihalides are shorter than expected for single bonds.

  4. $BeF _2$ is analogous to $CO _2$ and $BF _3$ analogous to $SO _3$

Show answer
Correct Option: A,C,D
Explanation:

(B) $BeF _2$ has $3C - 2e^-$ bond.

The correct statements are: 
(A) $BeCl _2$ tends to dimerize to a 3-coordinate structure in vapor phase which involves chlorine bridges, but linear monomer is also known at high temperature.
(C) Bond lengths in all the boron trihalides are shorter than expected for single bonds. This indicates presence of multiple bonds.
(D) $BeF _2$ is analogous to $CO _2$ as both have linear geometry. $BF _3$ analogous to $SO _3$ as both have plane triangular geometry.

A boron carbide rod is used in a nuclear reactor, because boron $( ^{10}B )$ has a very:

chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

  1. low area of cross-section for capturing neutrons

  2. high area of cross-section for capturing neutrons

  3. low area of cross-section for capturing protons

  4. high area of cross-section for capturing electrons

Show answer
Correct Option: B
Explanation:

The wide absorption spectrum of boron makes it suitable also as a neutron shield. Larger the cross-sectional area more the number of thermal neutrons get captured in a nuclear reactor.

Assertion : Diborane has two types of hydrogens.


Reason : By methylation only four hydrogen atoms of diborane are substituted forming $Me _{4}B _{2}H _{2}$.

chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

  1. Both Assertion and Reason are true and Reason is correct explanation of Assertion

  2. Both Assertion and Reason are true and Reason is not the correct explanation of Assertion

  3. Assertion is true but Reason is false

  4. Assertion is false but Reason is true

Show answer
Correct Option: A
Explanation:

Diborane has 4-termianl $B-H$ bonds and 2-bridged $B-H-B$ bonds. During methylation of diborane, all terminal $H$ atoms are replaced by methyl atoms.

Which one of the following compounds does not belong to the family of boranes?

chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

  1. $B _{5}H _{9}$

  2. $B _{5}H _{10}$

  3. $B _{5}H _{11}$

  4. $B _{6}H _{10}$

Show answer
Correct Option: B
Explanation:

Boranes have the general formulae as $B _{n} H _{n+4} $ or $B _{n} H _{n+6} $.

Hence, $B _5H _{10}$ is not a borane.

The total number of electrons shared between two boron atoms in $B _{2}H _{6}$ is :

chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

  1. 2

  2. 3

  3. 4

  4. 6

Show answer
Correct Option: C
Explanation:

There are 2 e- in each B-H-B bond. In total there are 2+ 2 =4 e- shared by the 2 boron atoms.

The mixture of $BCl _{3}$ vapour and hydrogen gas is subjected to electric discharge, The products obtained are:

chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

  1. B, HCl

  2. $B _{2}H _{6},HCl$

  3. $B _{2}H _{5}CI,HCl$

  4. $B _{2}H _{4}Cl _{2},HCl$

Show answer
Correct Option: B
Explanation:

$2BCl _{3} + 6H _{2} (excess)\xrightarrow[silent electric]{discharge} B _{2} H _{6} + 6HCl$

In diborane molecule hydrogen bridge bond is formed because boron has:

chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

  1. shortage of 4 electrons required for bonding

  2. shortage of 2 electrons required for bonding

  3. 4 electrons more than required for bonding

  4. 2 electrons more than required for bonding.

Show answer
Correct Option: B
Explanation:
  1. The bridge bonds are 3c-2e bonds. They have 2 electrons (4 in normal covalent). Thus in diborane boron is short of 2 electrons hence it forms hydrogen bridge.

Assertion (A) : When diborane is heated with $NH _{3}200^{0} C ,$ borazole is obtained :
Reason (R): Borazole is known as inorganic benzene :

chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

  1. Both A and R are true and R is correct

    explanation of A

  2. Both A and R are true and R is not correct

    explanation of A

  3. A is true but R is false

  4. A is false but R is true.

Show answer
Correct Option: B
Explanation:

$B _{2}H _{6}+2NH _{3}\overset {120^{0}C}{\rightarrow}B _{2}H _{6}.2NH _{3}\overset {200^{0}C}{\rightarrow} \underset {Borazole}{B _{3}N _{3}H _{6}} \overset {>200^{0}C}{\rightarrow} 3(BN) _{n}+3nH _{2}$
Borazole is also called borazine or inorganic benzene as its structure is very similar to benzene, with boron and nitrogen alternatively arranged instead of carbon and coordinate bond from nitrogen to boron instead of carbon-carbon double bond.