Tag: study of boron

Questions Related to 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 $
chemistry the p-block elements - group 13 study of diborane some important compounds of boron study of boron

  1. 36 kJ

  2. 509 kJ

  3. 520kJ

  4. -3550kJ

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Correct Option: D

$B _2H _6$ reacts with $O _2$ and $H _2O$ respectively to form: 

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

  1. $B _2O _3, H _3BO _3$

  2. $B _2O _3, BH _4^-$

  3. $HBO _2, H _3BO _3$

  4. $H _3BO _3, HBO _2$

Show answer
Correct Option: A
Explanation:
$B _2H _6 + 3O _2 \to B _2O _3 + 3H _2O$
$B _2H _6 + 6H _2O \to 2H _3BO _3 + 6H _2$

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

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

  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 $[BH _4]^-$

Show answer
Correct Option: C
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.

Which of the following statement about boron carbide is wrong?

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

  1. Its molecular formula is $B _4C$.

  2. It is also called Norbia.

  3. It is the hardest substance.

  4. It is used for cutting glasses.

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Correct Option: C
Explanation:

Boron carbide $B _4C$ is an extremely hard boroncarbon ceramic material used in tank armor, bulletproof vests, engine sabotage powders and  is called Norbia.

In the arts, silicon carbide is a popular abrasive in modern lapidary due to the durability and low cost of the material. In manufacturing, it is used for its hardness in abrasive machining processes such as grinding, honing, water-jet cutting and sandblasting. 

Particles of silicon carbide are laminated to paper to create sandpapers and the grip tape on skateboards.

Find the incorrect match.

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

  1. $Al _2Cl _6$ : $3C - 4e$ bond is present

  2. $Al _2(CH _3) _6$ : All carbon atoms are $sp^{3}$ - hybridized

  3. $I _2Cl _6$ : Nonplanar

  4. $Al _2Br _6$ : Nonpolar

Show answer
Correct Option: C
Explanation:

A) $Al _2Cl _6$ contains, $3C-4e$ bonds. In each such bond, two $Al$ atoms and one $Cl$ atom participate. Each $Al$ atom contributes $1$ electron and $Cl$ atom contributes $2$ electrons. Thus, the option A is correct.
B) In $Al _2(CH _3) _6$, all $C$ atoms are $sp^3$ hybridized and result in tetrahedral geometry. Thus, the option B is correct.
C) In $I _2Cl _6$, each iodine atom is $sp^3d^2$ hybridized with $4$ bond pairs and two lone pairs. Each iodine atom has square planar geometry. The repulsion between the lone pair of electrons on two iodine atoms will be minimized when the molecule is planar. Thus, the option C is incorrect.
D) $Al _2Br _6$ molecule is non planar as each $Al$ atom is $sp^3$ hybridized. Thus, the option D is correct.

Find out the similarities between $I _2Cl _6$ and $Al _2Cl _6$.

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

  1. Both have $3C\, -\, 4e^-$ bond

  2. Both have $sp^3$- hybridization for the central atom

  3. Both are nonplanar

  4. All are correct

Show answer
Correct Option: A
Explanation:

A)  Both $ I _2Cl _6$ and $ Al _2Cl _6$ have $ 3C\, -\, 4e^-$ bonds. Hence, option A is correct.
B) In $ I _2Cl _6$, the central $I$ atom undergoes $sp^3d^2$ hybridization and in $ Al _2Cl _6$, the central $Al$ atom undergoes $sp^3$ hybridization. Thus, the option B is incorrect.
C) $ I _2Cl _6$ is planar and $ Al _2Cl _6$ is non planar. Thus, the option C is incorrect.

Which of the following molecule has $3C\, -\, 4e^-$ bond?

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

  1. $Al _2Cl _6$

  2. $Be _2Cl _4$

  3. $I _2Cl _6$

  4. All are having $3C\, -\, 4e^-$ bond

Show answer
Correct Option: D
Explanation:

 $3C-4e^-$ bond is a model used to explain bonding in certain hypervalent molecules such as tetratomic & hexatomic interhalogen compounds, sulphur tetrafluoride, xenon fluoride and the fluoride ions.

$Al _2Cl _6$, $Be _2Cl _4$ and $I _2Cl _6$ contain $3C\, -\, 4e^-$ bond. The chlorine atoms acts as bridges and forms one covalent bond and other coordinate bond.

Which one of the following methyl diboranes does not exist?

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

  1. $B _2H _4(CH _3) _2$

  2. $B _2H _3(CH _3) _3$

  3. $B _2H _2(CH _3) _4$

  4. $B _2H(CH _3) _5$

Show answer
Correct Option: D
Explanation:

Di borane forms methyl diborane($B _2H _5(CH _3))$,dimethyl diborane($B _2H _4(CH _3) _2$),trimethyl diborane($B _2H _3(CH _3) _3$) ,tetramethyl diborane($B _2H _2(CH _3) _4$).

So $B _2H(CH _3) _5$ can not form,becuase in this compound we have to use bridge hydrogen for the formation of this compound,that never happens.

Hence option D is correct.

Identify the statement(s) that is/are correct as far as 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.

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Correct Option: A,B,C

Which of the following overlapping is used for the formation of $3C\, -\, 2e^-$ bond in chain polymer of $BeMe _2$ ?

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

  1. $sp\, -\, sp\, -\, sp$

  2. $sp^2\, -\, sp^2\,-\, sp^2$

  3. $sp^2\, -\, sp^3\, -\, sp^2$

  4. $sp^3\, -\, sp^3\, -\, sp^3$

Show answer
Correct Option: D
Explanation:

$sp^3\, -\, sp^3\, -\, sp^3$ overlapping is used for the formation of $3C\, -\, 2e^-$ bond in chain polymer of $BeMe _2$. Thus, the $Be$ atom and $C$ atom of each methyl group is $sp^3$ hybridized.