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

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

  1. There are two bridging hydrogen atoms in diborane

  2. Each boron atom forms four bonds in diborane

  3. All B - H bonds in diborane are similar
  4. Diborane contains 3c-2$e^{-}$ bonds
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In diborane, there are two types of B-H bonds: terminal and bridging. The terminal bonds are standard 2c-2e bonds, while the bridging bonds are 3c-2e bonds. Therefore, they are not all similar.

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

When an inorganic compound (X) having 3c-2e as well as 2c-2e bonds reacts with ammonia gas at a certain temperature and gives a compound(Y) iso-structural with benzene.Compound (X) with ammonia at a high temperature, produces a hard substance (Z).Then:

  1. X is $B _{2}H _{6}$

  2. Z is known as inorganic graphite

  3. Z having structure similar to graphite

  4. Z having structure similar to X
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Explanation

X is $B _2H _6$ having 3c-2e as well as 2c-2e bonds. $B _2H _6$ reacts with $NH _3$ to form borazine or inorganic benzene. Z is $(BN) _x$ is called inorganic graphite and has similar structure to graphite. The whole reaction is shown in figure.

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

In the reaction, $2X+B _{2}H _{6}\rightarrow [BH _{2}(X) _{2}]^{+}BH _{4}^{-}$, the amine(s) X is (are) :

  1. $NH _{3}$
  2. $CH _{3}NH _{2}$
  3. $(CH _{3}) _2NH$
  4. $(CH _{3}) _{3}N$
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Explanation

Smaller amines such as $NH _3$, $CH _3NH _2$ and $(CH _3) _2NH$ give unsymetrical cleavage of diborane according to following reaction
$2NH _3+B _{2}H _{6}\rightarrow [BH _{2}(NH _3) _{2}]^{+}BH _{4}^{-}$
Large amines such as $(CH _3) _3N$ give symmetrical cleavage of diborane according to following reaction
$B _2H _6 + 2N(CH _3) _3 \rightarrow 2(CH _3) _3N \rightarrow BH _3$

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

Select the incorrect statement 

  1. Diborane is $e^-$ deficient molecule

  2. Borazine is similar to benzene

  3. Baeyers's process is used to purify red Bauxite
  4. $BF _3$ is most acidic in boron trihalides
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

BF3 is actually the least acidic of the boron trihalides because of strong p-pi back-bonding from the fluorine atoms to the boron atom, which reduces the electron deficiency of the boron center.

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

Diborane is formed from the elements as shown in equation (1) $ 2B(s) +3H _2(g) \rightarrow B _2H _6(g) ......(1) $
The $ H^o$ for the reaction (1) is 
Given that 

$ { H } _{ 2 }O(\ell )\rightarrow H _{ 2 }O(g) $ $ \Delta { H } _{ 1 }^{ 0 }=44kJ $
$ 2B(s)+\frac { 3 }{ 2 } { O } _{ 2 }(g)\rightarrow B _{ 2 }O _{ 3 }(s) $ $ \Delta { H } _{ 2 }^{ 0 }=-1273kJ $
$ B _{ 2 }H _{ 6 }(g)+3O _{ 2 }(g)\rightarrow B _{ 2 }O _{ 3 }+3H _{ 2 }O(g) $ $ \Delta { H } _{ 3 }^{ 0 }=-2035kJ $
$ H _{ 2 }(g)+\frac { 1 }{ 2 } O _{ 2 }(g)\rightarrow H _{ 2 }O(\ell ) $ $ \Delta { H } _{ 4 }^{ 0 }=-286kJ $

  1. 36 kJ

  2. 509 kJ

  3. 520kJ

  4. -3550kJ
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Using Hess's Law, we combine the given equations to find the enthalpy of formation of B2H6. The calculation results in -3550 kJ based on the provided thermochemical data.

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

Which is/are correct for $B _2H _6$ structure ?

  1. It has $1\:B-H$ terminal bonds and two 3C-2e bonds
  2. It has $5\:B-H$ terminal bonds and two 3C-2e bonds
  3. It has $4\:B-H$ terminal bonds and two 3C-2e bonds and one $B-B$ bond
  4. It has ionic interaction between $[BH _2]^+$ and $[BH _4]^-$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

In the structure of diborane, $4$ terminal $B-H$ bonds are present. These are regular 2C-2e bonds.
In addition, two $B-H-B$ bridges are present. These are 3C-2e bonds.