Q. 10.16 - An Introduction to General, Organic, and Biological Chemistry

Question

Using Table 103, identify the stronger acid in each of the following pairs:

a. ${\mathrm{NH}}_4^{+}$or ${\mathrm{H}}_3{\mathrm{O}}^{+}$

b. ${\mathrm{H}}_2{\mathrm{SO}}_4$ or $\mathrm{HCN}$

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

Step-by-Step Solution

Answer

(Part a) ${\mathrm{H}}_3{\mathrm{O}}^{+}$ is a more powerful acid than ${\mathrm{NH}}_4^{+}$.

(Part b) ${\mathrm{H}}_2{\mathrm{SO}}_4$ is a more powerful acid than $\mathrm{HCN}$

(Part c) ${\mathrm{H}}_2{\mathrm{CO}}_3$  is a more powerful acid than  ${\mathrm{H}}_2\mathrm{O}$

Step 1: Introduction (Part a)

Acid-base Arrhenius systems:

Acid:

Acid is a chemical that increases the concentration of ${\mathbf{H}}^{\mathbf{+}}$ (hydrogen ion) in water, according to Arrhenius. For instance:

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

Base:

According to Arrhenius, a base is a chemical that raises the concentration of the hydroxide ion ${\mathrm{OH}}^{-}$in water. For instance:

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

Step 2: Bronsted-Lowry acid

Bronsted-Lowry acid-base system:

Acid:

Acid is a chemical that donates the${\mathrm{H}}^{+}$ (hydrogen ion), Bronsted-Lowry claims that. Bronsted-Lowry acid is a proton donor in general.

Base:

Bronsted-Lowry claims that, A base is a substance that absorbs hydrogen ions or proton${\mathrm{H}}^{+}$Bronsted-Lowry base is a proton acceptor in general.

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

  Acid   base

Step 3: Characteristics 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 do not fully ionize in solution, meaning they only ionize partially.

2. When weak acids are dissolved in water, they only create one hydrogen ion and its conjugated base.

3. For weak acids, the equilibrium cons have a tiny value.

Step 5: Strong Acids

The following are the characteristics of strong acids:

1. Strong acids fully ionize in solution.

2. When strong acids are dissolved in water, they create all the hydrogen ions that they contain.

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

Step 6: Conductivity of the solution

The concentration of ions determines the conductivity of the solution.

Because strong acid completely ionizes, the ion concentration is larger, and the conductivity is also higher.

Because the weak acid does not completely ionize, the concentration of ions is lower, and the conductivity is likewise lower.

Step 7: Explanation of (Part A)

${\mathrm{H}}_3{\mathrm{O}}^{+}$is a more powerful acid than ${\mathrm{NH}}_4^{+}$.

Step 8: Explanation of (Part B)

${\mathrm{H}}_2{\mathrm{SO}}_4$ is a more powerful acid than $HCN$.

Step 9: Explanation of (Part C)

${\mathrm{H}}_2{\mathrm{CO}}_3$ is a more powerful acid than ${\mathrm{H}}_2\mathrm{O}$