Tag: study of diborane

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

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

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

Assertion : Diborane has two types of hydrogens.


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

  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
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

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

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

  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.
Reveal answer Fill a bubble to check yourself
B Correct answer
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.
Multiple choice chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

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

  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.
Reveal answer Fill a bubble to check yourself
B Correct answer
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.

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

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

  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
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

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

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

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

  1. $Br _{2}$ at $100^{o}C$
  2. $HCl$ $/$anhydrous $AlCl _{3}$

  3. both A and B
  4. $Cl _{2}$ at $100^{o}C$
Reveal answer Fill a bubble to check yourself
C Correct answer
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.