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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.

Multiple choice chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron
All the $Al-Cl$ bonds in $Al _2Cl _6$ are equivalent.

  1. True

  2. False
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The given statement is False.
All the  $\displaystyle Al-Cl$ bonds in $\displaystyle Al _2Cl _6$ are not equivalent.
Two types of bonds are present in $\displaystyle Al _2Cl _6$, terminal $\displaystyle Al-Cl$ bonds that are normal $\displaystyle 2c-2e$ bonds and $\displaystyle Al-Cl-Al$ bridges that are $\displaystyle 3c-4e$ bonds.

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

From $B _2H _6$, all the following can be prepared except :

  1. $B _2O _3$
  2. $H _3BO _3$
  3. $B _2(CH _3) _6$
  4. $NaBH _4$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
$B _2H _6+3O _2\rightarrow B _2O _3+3H _2O+Heat$

$B _2H _6+6H _2O\rightarrow H _3BO _3+6H _2$

$2NaH+B _2H _6\rightarrow etherNaBH _4$

From $B _2H _6$, all can be prepared except $B _2(CH _3) _6$

Hence option $C$ is correct.