Tag: study of boron

Questions Related to study of boron

The number of simple covalent bonds (B-H) present in diborane:

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

  1. 2

  2. 4

  3. 6

  4. 8

Show answer
Correct Option: B
Explanation:
The molecular formula of diborane is $B _{2}H _{6}$
Diborane consists 2 3center-2electrons bonds and 4 2center-2electrons bonds.
In diborane, the two boron groups are bonded to each other by a bridge-like structure. Thus, it contains 4 covalent bonds.

Which of the following statement is correct for diborane ?

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

  1. Small amines like $NH _3,\, CH _3NH _2$ give unsymmetrical cleavage of diborane

  2. Large amines such as $(CH _3) _3N$ and pyridine gives symmetrical cleavage of diborane

  3. Small as well as large amines both gives symmetrical cleavage of diborane

  4. (A) and (B) both

Show answer
Correct Option: D
Explanation:

$Small\quad amines\ { B } _{ 2 }{ H } _{ 6 }+{ 2NH } _{ 3 }\rightarrow [{ H } _{ 2 }B\left( { NH } _{ 3 } \right) _{ 2 }]^{ + }[{ BH } _{ 4 }]^{ - }\ Large\quad amines\ { B } _{ 2 }{ H } _{ 6 }+2N\left( { CH } _{ 3 } \right) _{ 3 }\rightarrow 2{ H } _{ 3 }B\leftarrow N\left( { CH } _{ 3 } \right) _{ 3 }$

Which one of the following statement is not true regarding $B _2H _6$ ?

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

  1. It react with $NaH$ to form $NaBH _4$

  2. It is highly inflamable gas

  3. It contain four equal $B-H$ bonds

  4. It react with lewis base to form always adduct

Show answer
Correct Option: C
Explanation:

${B} _{2}{H} _{6}$ + $2NaH$ $\rightarrow$ $2 Na(B{H} _{4})$

It is highly Inflamable Gas and it reacts with Lewis base to form always adduct
It Doesn't contain 4 equal B-H bonds
So Option C is correct.

Boron halides behave as Lewis acids because of their ________ nature.

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

  1. proton donor

  2. covalent

  3. electron deficient

  4. ionising

Show answer
Correct Option: C
Explanation:

According to Lewis, the compound which can accept a lone pair of electron, are called acids.
Boron halides, being electron deficient compounds, can accept a lone pair of electrons, so termed as Lewis acid.

Diborane combines with ammonia at ${120}^{o}C$ to give:

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

  1. ${B} _{2}{H} _{6}.{NH} _{3}$

  2. ${B} _{2}{H} _{6}.2{NH} _{3}$

  3. ${B} _{2}{H} _{6}.3{NH} _{3}$

  4. none of the above

Show answer
Correct Option: B
Explanation:

Diborane combines with ammonia to form a borazine.

${ B } _{ 2 }{ H } _{ 6 }+2N{ H } _{ 3 }\rightarrow { B } _{ 2 }{ H } _{ 6 }.2N{ H } _{ 3 }$
The reaction proceeds further to form inorganic benzene.
$2{ B } _{ 2 }{ H } _{ 6 }.2N{ H } _{ 3 }\rightarrow 2{ B } _{ 3 }{ N } _{ 3 }{ H } _{ 6 }+12{ H } _{ 2 }$
Here, ${ B } _{ 3 }N _{ 3 }{ H } _{ 6 }$ is inorganic benzene.

Number of terminal hydrogen atoms present in diborane?

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

  1. 2

  2. 4

  3. 6

  4. 8

Show answer
Correct Option: B
Explanation:

Diborane is an electron deficient molecule. The two boron atoms and the four terminal hydrogen atoms of the molecule are all in the same plane. These four terminal B -H bonds are regular 2-centered- 2 electron bonds. The bridging hydrogen atoms lie above and below this plane.

Hence option B is correct answer.

Borazine is sometimes called inorganic benzene. Which of the following reactions is expected to give this compound?

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

  1. $B _{2}H _{6}+NH _{3} \xrightarrow [ excess\ { NH } _{ 3 } ]{ low\ tem } $

  2. $B _{2}H _{6}+NH _{3} \xrightarrow [ excess\ { NH } _{ 3 } ]{ high\ tem } $

  3. $B _{2}H _{6}+NH _{3} \xrightarrow [ ratio\ 2\ { NH } _{ 3 }:1{ B } _{ 2 }{ H } _{ 6 } ]{ high\ tem } $

  4. $All\ of\ these$

Show answer
Correct Option: C
Explanation:
Borazine is an inorganic compound with the chemical formula ${ (BH } _{ 3 }{ )(NH } _{ 3 })$ In this cyclic compound, the three BH units and three NH units alternate. The compound is isoelectronic and isostructural with benzene. Like benzene, borazine is a colourless liquid. For this reason, borazine is sometimes referred to as "inorganic benzene"

Borazine is synthesized from diborane and ammonia in a 1:2 ratio at 250–300 °C with a conversion of 50%.

$3B _2H _6 + 6NH _3 \rightarrow 2B _3H _6N _3 + 12H _2$

$BCl _3+LiAlH _4\rightarrow A+LiCl+AlCl _3$
$A+H _2O\rightarrow B+H _2$
$B\rightarrow C$.
in this reaction sequence A, B, and C compounds respectively are?

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

  1. $B _2H _6,B _2O _3,B$

  2. $B _2H _6,H _3BO _3,B _2O _3$

  3. $B _2H _6,H _3BO _3,B$

  4. $HBF _4,H _3BO _3,B _2O _3$

Show answer
Correct Option: B
Explanation:

The reactions given are,

$LiAlH _4 + BCl _3 \rightarrow B _2H _6 + LiCl + AlCl _3$
Hence A is $B _2H _6$

Now, second reaction is,
$B _2H _6 +H _2O \rightarrow H _3BO _3 +H _2$
Hence B is $H _3BO _3$

On heating B i.e. $H _3BO _3$ we get $B _2O _3$

$B _2H _6 + NH _3 \rightarrow$ Addition compound $(X)$
$(X) \overset{450K}{\rightarrow} Y + Z(g)$
In the above sequence $Y$ and $Z$ are respectively:

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

  1. borazine, $H _2O$

  2. boron, $H _2$

  3. boron nitride, $H _2$

  4. borazine and hydrogen

Show answer
Correct Option: D
Explanation:

$B _2H _6+2NH _3 \longrightarrow \underset {(X)}{B _2H _62NH _3}$

$3B _2H _62NH _3\xrightarrow[]{450K}\underset {(Y)}{2B _3N _3H _6}+\underset {(Z)}{3H _2}$
$(Y)$ & $(Z)$ are borazine and $H _2$ respectively.

Diborane belongs to the :

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

  1. ${ B } _{ n }{ H } _{ n+6 }$ series

  2. ${ B } _{ n }{ H } _{ n+1 }$ series

  3. ${ B } _{ n }{ H } _{ n+4 }$ series

  4. ${ B } _{ n }{ H } _{ n+8 }$ series

Show answer
Correct Option: C
Explanation:

The chemical formula for diborane is $B _2H _6$ which resembles general formula $B _n{H} _{n+4}$.