Chemistry

Acids and Bases

594 Questions

Acids and bases questions cover the chemical properties, common examples, and theoretical concepts of acidic and basic substances. Topics include identifying proton acceptors, recognizing amphoteric substances, and knowing the sources of everyday organic acids. These foundational chemistry questions are common across SSC, banking, and railways examinations.

Acid and base propertiesOrganic acidsAmphoteric substancesProton donors and acceptorsChemical formulas

Acids and Bases Questions

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 about $H _{3}BO _{3}$ is not correct?

  1. It is prepared by acidifying an aqueous

    solution of borax
  2. It has a layer structure in which planar $BO _{3}$ units are joined by hydrogen bonds

  3. It does not act as proton donor but acts as

    Lewis acid by accepting hydroxyl ion

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

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

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

$\mathrm{H} _{3}\mathrm{B}\mathrm{O} _{3}$ is:


  1. Monobasic and weak Lewis acid

  2. Monobasic and weak Bronsted acid

  3. Monobasic and strong Lewis acid

  4. Tribasic 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.

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

Boric acid is :

  1. monobasic and weak lewis acid

  2. monobasic and weak bronsted acid

  3. monobasic and strong lewis acid

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

Boric acid is monobasic acid and weak Lewis acid.


Boric acid contains $3-OH$ groups yet it acts as monobasic acid rather than tribasic acid. Because boric acid does not act as proton donor but it accepts a lone pair of electrons from $OH^{-}$ ions and forms ${B(OH) _4}^-$. Boric acid behaves as Lewis acid because it accepts a lone pair of electrons from $OH^{-}$ ions from water. 
Boric acid considered as weak acid because it does not dissociate to produce ions rather forms metaborate ion and in turn release ions.

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:

  1. strong tribasic acid

  2. strong monobasic acid

  3. weak tribasic acid

  4. weak monobasic acid
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Boric acid is a weak, monobasic lewis of boron often used as an antiseptic, insecticide, flame retardant, neutron absorber or precursor to other chemical compounds. It has the chemical formula,$H _3BO _3$ (sometimes written $B(OH) _3$ and exists in the form of colourless crystals or a white powder that dissolves in water.

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

On the addition of mineral acid to an aqueous solution of borax, the compound formed is:

  1. orthoboric acid

  2. boron hydride

  3. metabolic acid

  4. pyroboric acid
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Addition of mineral acid to an aqueous solution of Borax,

Orthoboric acid is formed.

$Na _2B _4O _7+2HCl+5H _2O\longrightarrow 4H _3BO _3 + 2NaCl$

Borax.        Hydrochloric      Orthoboric acid  Sodium chloride Acid

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

Acid melts at about $236^oC$, and when heated above about $300^o C$ further dehydrates, forming tetraboric acid, also called pyroboric acid $(H _2B _4O _7)$.

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

An aqueous solution of boric acid is found to be weakly acidic in nature. This acidic character arises due to the following reasons.

  1. It is a protic acid which donates protons in aqueous solution.
  2. It is a Lewis acid which abstracts $OH^-$ from water and leaves $H^+$ to make the solution acidic.

  3. It gives metaboric acid when dissolves in water

  4. It is prepared by reaction of borax with sulphuric acid hence it behaves as an acid.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Boric acid, when reacts with water, abstracts ${OH}^{-}$ ions and releases ${H _3O}^{+}$ ions.

$H _3BO _3 + H _2O \; \longrightarrow \; {H _3O}^{+} + {H _2BO _3}^{-}$
This property of boric acid makes it acidic.

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 statements is correct?

  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.
Reveal answer Fill a bubble to check yourself
C Correct answer
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.

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

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

  1. $H _{2}BO _{2}^{+}$
  2. $H _{2}BO _{2}^{-}$
  3. $[B\left ( OH \right ) _{4}]^{-}$
  4. $[B\left ( OH \right ) _{4}]^{+}$
Reveal answer Fill a bubble to check yourself
C Correct answer
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^{+} $

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

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

  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
Reveal answer Fill a bubble to check yourself
B Correct answer
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^{+} $

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

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

  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
Reveal answer Fill a bubble to check yourself
C Correct answer
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^{+} $

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

Boric acid:

  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.
Reveal answer Fill a bubble to check yourself
A,B,C,D Correct answer
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.