Tag: study of orthoboric acid

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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 statements regarding orthoboric acid $(H _3BO _3)$ is false?

  1. It acts as a weak monobasic acid.

  2. It is soluble in hot water.

  3. It has a planar structure.

  4. It acts as a tribasic acid.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Boric acid, also called hydrogen borate, , is a weak, monobasic lewis acid of boron

Option D only is the wrong statement because it acts as monobasic acid not tri basic .

Hence option D is correct.
Multiple choice chemistry the p-block elements - group 13 study of orthoboric acid some important compounds of boron study of boron

$B(OH) _3+NaOH\rightarrow Na[B(OH) _4] _{(aq)}$

Then addition of which of the following proceeds the reaction in the forward direction :

  1. cis-1, 2 diol

  2. trans 1, 2 diol

  3. borax
  4. $Na _2HPO _4$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

$B(OH) _3+NaOH\rightarrow Na[B(OH) _4] _{(aq)}$

This reaction is reversible reaction because sodium metaborate, $ Na [B(OH) _4]$ formed by the reaction between $B(OH) _3$ and NaOH gets hydrolysed to regenerate $B(OH) _3$ and NaOH.

$ Na [B(OH) _4]$ $\overset {hydrolysis}\rightarrow$ $NaOH$ + $B(OH) _3$

If, some quantity of polyhydroxy compounds like cis- 1, 2-diol, catechol, glycerol etc is added to the reaction mixture then the $B(OH) _3$ combines with such polyhydroxy compounds to give chelated complex compound. Due to complex compound formation, stability increases and due to higher stability of complex, reaction moves in forward direction.

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/are incorrect statement(s)?

  1. The hydroxide of aluminium is more acidic than that of boron.

  2. The hydroxide of boron is basic while that of aluminium is amphoteric.

  3. The hydroxide of boron is acidic while that of aluminium is amphoteric.

  4. The hydroxides of both boron and aluminium are amphoteric.
Reveal answer Fill a bubble to check yourself
A,B,D Correct answer
Explanation

All the elements of this group 13 form oxides and hydroxide.


Boron is the only element in group III of the periodic table which is non-metallic. Metal hydroxides must form a stable cation and anion i.e $OH^-$. Boron does not form a stable cation. This is the reason why metals form basic hydroxides while boron forms a weak acid called boric acid.

 Boron forms acidic oxides and hydroxides, while Al and Ga form amphoteric oxides and hydroxides. In and Tl forms basic oxides and hydroxides.The acidic nature of hydroxides decreases down the group.

Hence options A,B & D are 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 a very weak acid but in the presence of certain organic compounds, it acts as a strong acid. Which one of the following organic compound(s) cannot affect such change?

  1. Glycerol

  2. Acetic acid

  3. Ethyl alcohol

  4. Ethylene
Reveal answer Fill a bubble to check yourself
B,C,D Correct answer
Explanation


Option (B),(C),(D) are correct.
Boric acid forms a stable cyclic complex with polyhydroxy compounds like glycerol. This helps in the release of $H^+$ as $H _3O^+$ and therefore boric acid acts as a strong acid. This is not possible with compounds such as acetic acid, ethyl alcohol and ethylene.
Multiple choice chemistry the p-block elements - group 13 study of orthoboric acid some important compounds of boron study of boron

$2B+3H _{2}SO _{4}\rightarrow 2H _{3}BO _{3} +A$ 


The hybridization of central atom in compound A is :

  1. sp
  2. $sp^{2}$
  3. $sp^{3}$
  4. $sp^{3}d$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The balanced chemical reaction is as given below.
$2B+3H _{2}SO _{4}\rightarrow 2H _{3}BO _{3}\rightarrow + \underset {A} {SO _2}$
S atom in sulphur dioxide undergoes $sp^2$ hybridization.

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

$H _{3}BO _{3}\xrightarrow{375K} A \xrightarrow{Red \, Heat}B _{2}O _{3}$
$H _{3}BO _{3}\xrightarrow{435K} B \xrightarrow{Red \, Heat}B _{2}O _{3}$


The compounds A & B are:

  1. Orthoboric acid, metaboric acid

  2. Metaboric acid, Tetra boric acid

  3. Tetra boric acid, Metaboric acid

  4. Tetra boric acid, orthoboric acid
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$H _{3} BO _{3} \overset{375K}{\rightarrow} HBO _{2} \overset{red heat}{\rightarrow} B _{2} O _{3} $
$H _{3} BO _{3} \overset{435K}{\rightarrow} H _{2} B _{4} O _{7} \overset{red heat}{\rightarrow} B _{2} O _{3} $

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

Which is the correct statement for $H _{3}BO _{3}$ ?

  1. It is used as antiseptic

  2. As preservative of foods

  3. It gives green colour to flame

  4. All are correct
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

It is antiseptic and its water solution is used as an eyewash. It is used as a preservative.
Boron burns with green flame when heated strongly with $O _{2} $.