Q. 10.18 - An Introduction to General, Organic, and Biological Chemistry

Question

Identify the weaker acid in each of the following pairs:

a. ${\mathrm{HNO}}_3$ or ${\mathrm{HCO}}_3^{-}$

b. ${\mathrm{HSO}}_4^{-}$or ${\mathrm{H}}_2\mathrm{O}$

c. ${\mathrm{H}}_2{\mathrm{SO}}_4$ or ${\mathrm{H}}_2{\mathrm{CO}}_3$

Step-by-Step Solution

Answer

(Part a) ${\mathrm{HCO}}_3^{-}$ is a less powerful acid than ${\mathrm{HNO}}_3$

(Part b) ${\mathrm{H}}_2\mathrm{O}$ is a less powerful acid than ${\mathrm{HSO}}_4^{-}$

(Part c) ${\mathrm{H}}_2{\mathrm{CO}}_3$ is a less powerful acid than ${\mathrm{H}}_2{\mathrm{SO}}_4$

Step 1: Introduction (Part a)

Acid-base Arrhenius systems:

Acid:

According to Arrhenius, acid is a substance that raises the concentration of (hydrogen ion) in water. Consider the following:

$\mathrm{HCl}\stackrel{\mathrm{H},0}{⟶}{\mathrm{H}}^{+}+{\mathrm{Cl}}^{-}$

Base:

A base is a substance that enhances the concentration of the hydroxide ionic water, according to Arrhenius. Consider the following:

$\mathrm{NaOH}\stackrel{\mathrm{H},\mathrm{O}}{⟶}{\mathrm{Na}}^{+}+{\mathrm{OH}}^{-}$

Step 2: Bronsted-Lowry acid

Bronsted-acid-base Lowry's system:

Acid:

Acid, according to Bronsted-Lowry, is a chemical that provides the proton or (hydrogen ion). Bronsted-Lowry acid is a proton donor in general.

Base:

A base, according to Bronsted-Lowry, is a material that accepts the hydrogen ion or proton; A proton acceptor is a Bronsted-Lowry base in general.

$\mathrm{HCl}+{\mathrm{NH}}_3\to {\mathrm{NH}}_4^{+}+{\mathrm{Cl}}^{-}$

Acid   base

Step 3: Features of acids and bases

The following are some other features of acids and bases:

Acids and bases are both electrolytes.

Taste:

Acid has a sour flavour, whereas base has a harsh, chalky flavour.

Feel:

Acid has a stinging sensation, whereas base has a soapy, slick sensation.

Litmus paper retaliation:

Litmus paper changes colour from blue to red when exposed to acid, and red to blue when exposed to base.

Colour of phenolphthalein:

In phenolphthalein solution, acids are colorless, while bases are pink.

Neutralization:

Bases neutralize acids, and acids neutralize bases.

Step 4: Weak Acids

The following are features of weak acids:

1. Weak acids only partially ionize in solution, meaning they do not fully ionize.

2. Weak acids only produce one hydrogen ion and its conjugated base when dissolved in water.

3. The value of the equilibrium constant$\left(K_a\right)$Is tiny for weak acids.

Step 5: Strong Acids

Strong acids have the following characteristics:

1. In solution, strong acids totally ionize.

2. When strong acids dissolve in water, all the hydrogen ions they contain are released.

3. The value of the equilibrium constant $\left(K_a\right)$ This is significant for strong acids.

Step 6: Conductivity of the solution

The conductivity of a solution is determined by the ion concentration. Because strong acid completely ionizes, the ion concentration is larger, and the conductivity is also higher.

The concentration of ions is smaller, and the conductivity is thus lower, because the weak acid does not completely ionize.

Step 7: Explanation of (Part A)

${\mathrm{HCO}}_3^{-}$ is a less powerful acid than ${\mathrm{HNO}}_3$.

Step 8: Explanation of (Part B)

${\mathrm{H}}_2\mathrm{O}$ is a less powerful acid than ${\mathrm{HSO}}_4^{-}$

Step 9: Explanation of (part C)

${\mathrm{H}}_2{\mathrm{CO}}_3$ is weaker acid as compare to ${\mathrm{H}}_2{\mathrm{SO}}_4$.