Tag: some important compounds of boron

Questions Related to some important compounds of boron

Which of the following is not an application of orthoboric acid ?

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

  1. As an antiseptic and eye wash

  2. In glass industry 

  3. In glazes for pottery

  4. In borax-bead test

Show answer
Correct Option: D
Explanation:
Orthoboric acid is a weak, monobasic Lewis acid of boron, which is often used as an antiseptic, insecticide, flame retardant, neutron absorber, or precursor to other chemical compounds.

Borax on heating gives $B _2O _3 \; and \; NaBO _2$ which is glassy mass and used for the borax-bead test. Thus, there is no use of orthoboric acid in borax bead test.

Hence, the correct answer is option $\text{D}$.

Which one of the following statements is correct?

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

  1. Boric acid is a protonic acid.

  2. Both $Tl^{3+}$ and $Al^{3+}$ions act as oxidising agents in aqueous solution.

  3. Hydrogen bonding in $H _3BO _3$ gives it a layered structure.

  4. $B(OEt) _3$ imparts blue colour to the burner flame.

Show answer
Correct Option: C
Explanation:

$(A)$ Boric acid is a weak monobasic Lewis acid, soluble in water and in aqueous solutions. The boron atom completes its octet by accepting $OH^-$ from water molecules.
$B(OH) _3+2H _2O\rightarrow [B(OH) _4]^-+H _3O^+$
$(B)$ Only $Tl^{3+}$ acts as an oxidising agent on account of inert pair effect.
$(C)$ In the solid state, the $B(OH) _3$ units are hydrogen bonded together into two dimensional sheets with almost hexagonal symmetry. This gives it a layered structure.
$(D)$ $B(OEt) _3$ imparts green colour to the burner flame.

Hence, option C is the correct answer.

The reaction,

$B(OH) _3+NaOH\rightarrow Na[B(OH) _4]$ can be made to proceed in forward direction by :

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

  1. adding cis-1, 2-diol.

  2. adding borax.

  3. adding trans-1, 2-diol.

  4. adding $Na _2HPO _4$.

Show answer
Correct Option: A
Explanation:
If polyhydroxy compound like glycerol, mannitol or sugar are added to titration mixture than it can be titrated with $NaOH$.

Due to formation of chelated complex, the reaction moves in forward direction.

$B(OH) _{3}+NaOH\rightarrow Na[B(OH) _{4}]$

Aqueous solution of ortho-boric acid can be titrated against sodium hydroxide using phenolphthalein indicator only in presence of :

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

  1. trans-glycerol.

  2. catechol.

  3. cis-glycerol.

  4. both (b) and (c).

Show answer
Correct Option: D
Explanation:

Aqueous solution of ortho-boric acid can be titrated against sodium hydroxide using phenolphthalein indicator only in presence of catechol and cis-glycerol.

Ortho-boric acid forms a stable cyclic complex with polyhydroxy compounds like catechol and cis-glycerol. This helps in the release of $H^+$ as $H _3O^+$ and therefore boric acid acts as a strong acid and hence can be titrated against NaOH with phenolphthalein.

Hence,option D is correct.

Orthoboric acid behaves as weak monobasic acid giving $H {3}O^{+}$ and ___.

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

  1. $H _{2}BO _{2}^{+}$

  2. $H _{2}BO _{2}^{-}$

  3. $[B\left ( OH \right ) _{4}]^{-}$

  4. $[B\left ( OH \right ) _{4}]^{+}$

Show answer
Correct Option: C
Explanation:

It is a Lewis acid. It accepts an electron pair from $OH^{-}$.
The reaction follows:
$B(OH) _{3} + 2H _{2} O \rightleftharpoons [B(OH) _{4} ]^{-} +H _{3} O^{+} $

Ortho-boric acid can be represented as $B\left ( OH \right ) _{3}$. It is :

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

  1. a strong Arrhenius acid

  2. lewis acid and ionizes as monobasic acid

  3. an alkali capable of releasing $OH^{-}$ ions in water

  4. a weak acid existing as $B\left ( OH \right ) _{6}^{-3}$ in water

Show answer
Correct Option: B
Explanation:

It is a monobasic (releases 1 H+ )lewis acid. It accepts an electron pair from $OH^{-}$.
$B(OH) _{3} + 2H _{2} O \rightleftharpoons [B(OH) _{4} ]^{-} +H _{3} O^{+} $

Asseriton : In water, orthoboric acid behaves as a week monobasic acid.
Reason : In water, orthoboric acid act as a proton donor

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

  1. Assertion is true, Reason is true, Reason is the correct explanation of Assertion

  2. Assertion is true, Reason is true, Reason is not the correct explanation of Assertion

  3. Assertion is true, Reason is false

  4. Assertion is false, Reason is true

Show answer
Correct Option: C
Explanation:

It is a monobasic (releases 1 H+ )lewis acid. It accepts an electron pair from $OH^{-}$.
$B(OH) _{3} + 2H _{2} O \rightleftharpoons [B(OH) _{4} ]^{-} +H _{3} O^{+} $

Boric acid:

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

  1. exists in polymeric form due to inter-molecular hydrogen bonding

  2. it used in manufacturing of optical glasses

  3. is a tri-basic acid

  4. with borax, it is used in the preparation of a buffer solution.

Show answer
Correct Option: A,B,C,D
Explanation:

Boric acid, also called hydrogen borate, boracic acid, orthoboric acid the chemical formula $H _3BO _3$ ($B(OH) _3$) (mono basic), and exists in the form of colorless crystals or a white powder that dissolves in water.
Boric acid, exists in polymeric form due to inter-molecular hydrogen bonding
Boric acid is in equilibrium with its conjugate base the borate ion which is widely used (in the concentration range 50 - 100 ppm boron equivalents) as a primary or adjunct pH buffer system in swimming pools(buffer solution).
The primary industrial use of boric acid is in the manufacture of monofilament fiberglass usually referred to as textile fiberglass
Hence options A,B, C& D are correct.

When orthoboric acid is strongly heated, residue are :

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

  1. meta boric acid

  2. boron

  3. both

  4. none of these

Show answer
Correct Option: A
Explanation:

Boric acid is soluble in boiling water. When heated above 170 °C, it dehydrates, forming metaboric acid ($HBO _2$)

$H _3BO _3\rightarrow HBO _2 + H _2O$
Hence option A is correct.

Which of the following statements about $H _3BO _3$ is not correct?

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

  1. It is a strong tribasic acid

  2. It is prepared by acidifying an aqueous solution of borax

  3. It has a layer structure in which planar borate ions are joined by hydrogen bonding

  4. None of these

Show answer
Correct Option: A
Explanation:

Boric acid, also called hydrogen borate is a weak, monobasic Lewis acid of boron. So it is not a strong tribasic acid. Remaning all options are correct

Hence option $A$ is correct.