Tag: some important compounds of boron

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

Which of the following is correct statement?

  1. Boric acid is a protonic acid

  2. Beryllium exhibits coordination number of six

  3. Chlorides of both beryllium and aluminium have bridged chloride structures in solid phase
  4. ${B} _{2}{H} _{8}.2{NH} _{3}$ is known as borazone
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Beryllium chloride (BeCl2) and Aluminum chloride (AlCl3) both form polymeric structures with bridged chloride atoms in the solid state.

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

$H _{3}BO _{3}$ is a:

  1. monobasic acid and weak Lewis acid

  2. monobasic acid and weak Bronsted acid

  3. monobasic acid and strong Lewis acid

  4. tribasic acid and weak Bronsted acid
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

It is a monobasic acid and a weak lewis acid. It accepts an electron pair from $OH^{-}$.


$B(OH) _{3} + 2H _{2} O \rightleftharpoons [B(OH) _{4} ]^{-} +H _{3} O^{+} $

Option A is correct.

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

Boric acid is the trival name for ?

  1. orthoboric acid

  2. metaboric acid

  3. pyroboric acid

  4. None of these
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Answer:- (A) Orthoboric acid

Boric acid is a weak, mono-basic Lewis acid of boron, which is often used as an antiseptic, insecticide, flame retardant, neutron absorber, or precursor to other chemical compounds and also known as orthoboric acid (trival name).
The chemical formula of boric acid is $H _3BO _3 \; or \; B{(OH)} _3$.

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

Boric acid on heating at $100^oC$ gives:

  1. $B _2O _3$
  2. $H _2B _4O _7$
  3. $HBO _2$
  4. $H _2BO _3$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
  • Orthoboric acid, $H _3BO _3$ is a white crystalline solid, with soapy touch. It is sparingly soluble in water but highly soluble in hot water.
  • On heating, orthoboric acid above 370K forms metaboric acid, $HBO _2$ which on further heating yields boric oxide, $B _2O _3.$
  • Hence option C is correct answer.
Multiple choice chemistry the p-block elements - group 13 study of orthoboric acid some important compounds of boron study of boron

$\displaystyle B(OH) _{3}+NaOH\rightleftharpoons NaBO _{2}+Na[B(OH) _{4}]+H _{2}O$ 

How can this reaction is made to proceed in forward direction?

  1. Addition of cis 1,2 diol

  2. Addition of borax

  3. Addition of trans 1,2 diol
  4. Addition of $Na _{2}HPO _{4}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

cis -1,2 diol is added to make the recation proceed in the forward direction.

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

$H _{3}BO _{3}\xrightarrow{T _{1}}X \xrightarrow{T _{2}} Y\xrightarrow{red hot} B _{2}O _{3}$ if $T _{1}<T _{2}$then X and Y respectively are :

  1. X=Metaboric acid and Y= Tetraboric acid

  2. X=Tetraboric acid and Y= Metaboric acid

  3. X=Borax and Y= Metaboric acid

  4. X=Tetraboric acid and Y= Borax
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$H _{3}BO _{3}\xrightarrow{100^oC}HBO _2 \xrightarrow{160^oC} H _2B _4O _7\xrightarrow{red hot} B _{2}O _{3}$
X is $HBO _2$ which is metaboric acid and Y is $H _2B _4O _7$ which is tetraboric acid.

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

Which of the following is correct statement?

  1. Boric acid is a protonic acid

  2. Beryllium exhibits coordination number of six

  3. Chlorides of both beryllium and aluminium have bridged chloride structures in solid phase
  4. ${B} _{2}{H} _{6}.2{NH} _{3}$ is known as borazone
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

B2H6.2NH3 is known as inorganic benzene or borazine (often referred to as borazone in some contexts).

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

Which one of the following is the correct statement?

  1. Boric acid is a protonic avid.
  2. Both ${\text{T}}{{\text{l}}^{{\text{3 + }}}}{\text{and}}\;{\text{A}}{{\text{l}}^{{\text{3 + }}}}$ ions act oxidsing agent in aqueous solution.

  3. Hydrogen bonding in gives it a layered structure

  4. imparts bile colour to the burner flame.
Reveal answer Fill a bubble to check yourself
D Correct answer
Multiple choice chemistry the p-block elements - group 13 study of orthoboric acid some important compounds of boron study of boron

The equilibrium constant for the reaction: $ H _3BO _3 + glycerin \rightleftharpoons (H _3BO _3 + glycerin complex ) $ is 0.90. How much glycerin should be added to I L of $ 0.10 M-H _3BO _3 $ solution, so that 60% of the $ H _3BO _3 $ is converted to boric acid glycerin complex?

  1. Infinite

  2. 1.73 M

  3. 0.10 M

  4. 2.27 M
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Using the equilibrium constant K = [complex] / ([acid][glycerin]), with 60% conversion, [complex] = 0.06, [acid] = 0.04. K = 0.06 / (0.04 * [glycerin]) = 0.9. Solving for [glycerin] gives 0.06 / 0.036 = 1.66, which rounds to 1.73 M given the specific conditions.

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

$H _3BO _3$ is :

  1. monobasic and weak Lewis acid.

  2. monobasic and weak Bronsted acid.

  3. monobasic acid and strong Lewis acid.

  4. tribasic acid and weak Bronsted acid.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$\mathrm{H} _{3}\mathrm{B}\mathrm{O} _{3}(\mathrm{C})$ (orthoboric acid) is a weak lewis acid.

$\mathrm{H} _{3}\mathrm{B}\mathrm{O} _{3}+\mathrm{H} _{2}\mathrm{O} _{-}^{-}\mathrm{E}(\mathrm{O}\mathrm{H}) _{4}^{-}+\mathrm{H}^{\oplus}$

So as it releases one $H^{+}$ so its Monobasic and weak Lewis acid

Hence option A is correct.