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(D) \(H_2 SO_4 ,HSO_4^-\)

An acid and a base which differ only by the presence or absence of a proton are called a conjugate acid-base pair.

Here, \(H_2SO_4\), is acid and \(HSO^-_4\) is its conjugate base.

Option : (d) H₂SO₄,\(HSO^-_4\)

(a) +1

0.05 M dibasic acid gives 0.1 M \(H^+\) ions.

Therefore,

\(P^H=-\log\,[\,H^+]=-\log 10^{-1}\)

\(P^H=+1\)

Option : (a) +1

• Since ammonia molecule, NH₃ has a lone pair of electrons to donate it acts as a Lewis base. 
• AlCl₃ is a molecule with incomplete octet hence it is electron deficient and acts as a Lewis acid.

Given : 

Degree of dissociation = α = 0.0232 

Concentration of NH₄OH = C = 0.5 M 

Dissociation constant = K_b = ?

K_b = Cα²

= 0.5 × (0.0232)²

= 2.692 × 10^-4

∴ Dissociation constant of NH₄OH = K_b = 2.692 × 10^-4

(D) Temperature is increased

The ionic product of water will increase, if temperature is increased because dissociation constant only depends on the temperature.

Option : (d) Temperature is increased

Limitations of Arrhenius theory :

1. This theory is applicable only for aqueous solutions and not for non-aqueous solutions.

2. It fails to explain the acidic nature of non-hydrogen compounds like BF₃, AlCl₂, FeCl₃, etc.

3. It fails to explain the basic nature of non-hydroxy compounds like NH₃, amines, Na₂CO₃, KCN, aniline, etc. in their aqueous solutions.

4. It does not explain role of solvent or existence of H₃O⁺ in an aqueous solution of an acid.

(C) \(1.6 × 10^{-6}\)

 \(K_a=\frac{[B^+][\overset{-}{o}{H}]}{[BOH]}\)

\(K_a=\frac{C^2\alpha^2}{C(1-\alpha)}\)

\(\alpha=\frac{0.4}{100}=0.004\)

\(\therefore K_a=\frac{C\alpha ^2}{(1-\alpha)}\)

\(K_a= C\alpha ^2\)

\(\because \alpha <<1\)

\(K_a=0.1\times(4\times10^{-3})^2\)

= \(0.1\times16\times10^{-6}\)

= \(16\times10^{-7}\) or \(1.6\times10^{-6}\)

Option : (c) 1.6 × 10^-6

(c) a hydrogen ion exists freely in an aqueous solution.

According to the Arrhenius theory - An acid is a substance which releases \(H^+\) ions on dissolving in water. A base is a substance which releases \(OH^-\) ions on dissolving in water.

Option : (c) a hydrogen ion exists freely in an aqueous solution.

(b) an electrophile

According to the Lewis theory,

A Lewis acid has tendency to accept electrons. because they are electron deficient species. as we know electron deficient species also known as electrophile.

Option : (b) an electrophile

Even if monobasic acid and dibasic acid give same pH, their molar concentrations are different. One mole of monobasic acid like HCl gives 1 mol of H⁺ while one mole of dibasic acid gives 2 mol of H⁺ in solution. Hence the concentration of dibasic acid will be half of the concentration of monobasic acid. For example, for same pH. [Monobasic acid] = [Dibasic acid]/2.

Since the increase in temperature, increases the dissociation of water, its pH decreases.

(C) \(HSO_4^-\)

\(HSO_4^-\) can behave both as a conjugate acid and base.

\(\underset{\text{acid}}{HSO^-_4}\longrightarrow H^+\underset{\text{conjugate base}}{SO^-_4}\)

\(\underset{\text{base}}{HSO^-_4}\longrightarrow H^+\underset{\text{conjugate acid}}{H_2SO_4}\)

Option : (c) \(HSO^-_4\)

(A) \(NH_3\)

An acid and a base which differ only by the presence and Absence of a proton are called conjugate acid - base pair.

Here, \(NH^-_2\) is a base, therefore its conjugate acid will be \(NH_3.\)

Option : (a) NH₃

Degree of dissocsavIt is defined as a fraction of total number of moles of an electrolyte that dissociate into its ions at equilibrium.

It is denoted by a and represented by,

α = \(\frac{number\,of\,moles\,dissociated}{total\,number\,of\,moles\,an\,electrolyte}\)

OR,

α = \(\frac{Percent\,dissociation}{100}\)

∴ Percent dissociation = α × 100

Buffer solution : It is defined as a solution which resists the change in pH even after the addition of a small amount of a strong acid or a strong base or on dilution or on addition of water.

Sodium benzoate added to jams and jellies in commercial products maintains the pH constant and acts as a preservative. Hence jams and jellies are not spoiled for a very long time unlike homemade products.