Most Expected Questions for Chemical Science Students

Most Expected Questions on Acid and Base Chemistry (Download PDF)

1. Identify the acids in the following two reactions

CIF₃ and XeO₃
CIF₃ and OH^-
NOF and OH^-
NOF and XeO₃

2. The softest acid amongst the following is

Al3+
Li+
Ca2+
Ag+

3. Select the statement which satisfies correctly for CoF₆^-3, CoI₆^-3, AgI₂^-, AgF₂^-.

CoF₆^-3 and AgF₂^- are stable but CoI₆^-3 and AgI₂^- do not exist.
CoF₆^-3 and AgI₂^- are stable but CoI₆^-3 and AgF₂^- do not exist.
CoI₆^-3 and AgF₂^- are stable but CoF₆^-3 and AgI₂^- do not exist.
CoI₆^-3 and AgI₂^- are stable but CoF₆^-3 and AgF₂^- do not exist.

4. Identify the products for the following reactions:

P= BrF₂⁺ Q= BrF₄^- R= BrF₂⁺ S= SbF₆
P= BrF₂⁺ Q= BrF₅ R= BrF₂⁺ S= SbF₄^-
P= BrF₄⁺ Q= BrF₆^- R= BrF₄^- S= SbF₆⁺
P= BrF₄⁺ Q= BrF₂^- R= BrF₂⁺ S= SbF₆^-

5. What is the order of stability for the following compound:

I. [Cr (NH₃)₅F]₂+

II. [Cr (NH₃)₅I]₂+

III. [Cr (NH₃)₅ Br]₂+

I>II>III
III>I>II
II>I>III
I>III>II

6. Among the options given below, which one of the following is the correct sequence of increasing acid strength?

Me₃B < BH₃ < BF₃
BF₃ < BH₃ < Me₃B
Me₃B < BF₃ < BH₃
BF₃ < Me₃B < BH₃

7. In the following:

Species behaving as Bronsted- Lowry acids are

P, S
P, R
Q, R
Q, S

8. According to the HSAB principle, which of the following stable complexes are formed by Co₂⁺ & Pd₂⁺ ions?

[Pd (SCN)4]^-2 and [Co (NCS)4]^-2
[Pd (SCN)4]^-2 and [Co (SCN)4]^-2
[Pd (NCS)4]^-2 and [Co (NCS)4]^-2
[Pd (NCS)4]^-2 and [Co (SCN)4]^-2

9. When it comes to the bonding of the ligands Me₃N and Me₃P with the metal ions Be²⁺ and Pd²⁺, the accurate statement is,

The ligands bind equally strong with both the metal ions as they are dicationic.
The ligands bind equally strong with both the metal ions as both the ligands are pyramidal.
The binding is stronger for Me₃N with Be²⁺ and Me3P with Pd²⁺.
The binding is stronger for Me₃N with Pd²⁺ and Me3P with Be²⁺.

10. Which of the following is not true regarding H[B(HSO4)4]?

It is a stronger acid than HSO₃F.
It acts as a strong acid in H₂SO₄.
It can be prepared by dissolving boric acid in the oleum.
It cannot be titrated against KHSO₄.

Solutions

Solution 1.

Anion acceptors are acidic and anion donors are bases.

Solution 2.

Soft acids are larger and more polarizable, Hence Ag+ is the softest acid among Al₃⁺, Li₃⁺ and Ca₂⁺.

Solution 3.

AgI₂^- is stable but AgF₂^- does not exist. Since Ag⁺ is a soft acid, F^- is a hard base, and I^- is a soft base. Hence, AgI₂ (soft acid + soft base) is a stable complex and AgF₂^- (soft acid + hard base) does not exist.

Similarly, it is found that CoF₆^-3 (hard acid + hard base) is more stable than CoI₆^-3 (hard acid + soft base).

Solution 4.

A high specific conductance of liquid BrF₃ indicates that it ionises as:

SbF₅ acts as an acid in liquid BrF₃ because it increases the concentration of BrF₂+ ions as shown -

Solution 5.

According to the HSAB principle, hard acid interacts with hard base to form a stable complex, so in complex I, all ligands are hard base, and metal is also hard, so, it will form a stable complex than others. In II, the hard metal ion interacts with hard base NH3 and soft base I- so, it forms less stable complex than I and III while in III, the hard metal ion interacts with hard base NH3 and Br- which is border line base, so, it is stable than II.

So, the stability order will be as follows:

I>III>II

Solution 6.

Lewis acids are electron deficient species. If species contain more deficient central atoms, then its Lewis acidic strength is very high. F is an electron withdrawing group due to which it will make B more deficient but on the other hand, it decreases the deficiency by back bonding. While H is unable to do such a back bonding due to absence of lone pair. Me is an electron releasing group, thus making the boron the least electron deficient.

Solution 7.

Solution 8.

According to the HSAB principle, soft acid prefers to bind with a soft base, and hard acid prefers to bind with a hard base. [SCN]- is an ambidentate ligand. It coordinates through S-atoms to form complex [Pd (SCN)₄]^-2 because Pd₂⁺ is a soft acid that prefers to bind with soft S atoms. Whereas with Co²⁺, a hard acid prefers to bind with a hard N-atom to form complex [Co (NCS)₄]^-2.

Solution 9.

According to Pearson's HSAB principle, hard acids prefer binding to the hard bases to give ionic complexes, whereas the soft acids prefer binding to soft bases to give covalent complexes. NMe₃ is a hard ligand while PMe₃ is a soft ligand. Therefore, NMe3 binds with hard acid (metal ion) Be++ and PMe3 binds with soft acid (metal ion) Pd++.

Solution 10.

It is a superacid stronger than HSO3F and H2SO4.It can be prepared with the help of reaction:

H₃BO₃ + 2H₂SO₄ + 3SO₃ [H₃SO₄]+ + [B(HSO₄)₄]^-