Tag: study of diborane

Questions Related to study of diborane

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.

Identify the statement that is not correct as far as the structure of diborane is concerned: 

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

  1. there are two bridging hydrogen atoms in

    diborane

  2. each boron atom forms four bonds in diborane

  3. the hydrogen atoms are not in the same plane

    in diborane

  4. all B-H bonds in diborane are similar

Show answer
Correct Option: D
Explanation:

There are 4 2c-2e B-H bonds and 2 3c-2e bonds in diborane.

In diborane, the Tau-bonds can be formed by the overlapping of orbitals :

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

  1. $sp^{3}-s-sp^{3}$

  2. $sp^{3}-sp^{3}$

  3. $sp^{2}-sp^{3}$

  4. $sp^{2}-s-sp^{2}$

Show answer
Correct Option: A
Explanation:

In diborane, ${sp}^{3}$ hybrid orbital from each boron overlaps with 1$s$ orbital of $H$ atom to form 3 center-2 electron (3c-2e) bond.

$B _{2}H _{6}$ undergoes substitution reaction with:

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

  1. $Br _{2}$ at $100^{o}C$

  2. $HCl$ $/$anhydrous $AlCl _{3}$

  3. both A and B

  4. $Cl _{2}$ at $100^{o}C$

Show answer
Correct Option: C
Explanation:

$B _2H _6 + HCl \rightarrow B _2H _5Cl + H _2$
This reaction takes place in the presence of anhydrous $AlCl _3$.
$B _2H _6 + Br _2 \rightarrow B _2H _5Br + HBr$
This is a slow reaction taking place at $100^oC$.
$B _2H _6 + 6Cl _2 \rightarrow 2BCl _3 + 6HCl$
This is a vigorous reaction taking place at $25^oC$. Diborane does not react with $Cl _2$ at ${100}^{o}C$. This reaction is not reported.