Question

Classify each of the following Arrhenius acids as strong or weak given the degree of ionization: (a) acetic acid, \(\mathrm{HC}_{2} \mathrm{H}_{3} \mathrm{O}_{2}(a q), \sim 1 \%\) (b) carbonic acid, \(\mathrm{H}_{2} \mathrm{CO}_{3}(a q), \sim 1 \%\) (c) chlorous acid, \(\mathrm{HClO}_{2}(a q), \sim 1 \%\) (d) chloric acid, \(\mathrm{HClO}_{3}(a q), \sim 100 \%\)

Short answer

(a) Weak, (b) Weak, (c) Weak, (d) Strong

Step-by-step solution

Understanding Arrhenius Acids

Arrhenius acids are substances that increase the concentration of hydrogen ions (H^+) when dissolved in water. The strength of Arrhenius acids is determined by their degree of ionization in solution. A strong acid ionizes completely (100%), while a weak acid ionizes only partially (less than 100%).

Evaluate Acetic Acid

Acetic acid, HC_2H_3O_2, ionizes around 1% in water. This partial ionization indicates that acetic acid is a weak acid because it does not dissociate completely in solution.

Evaluate Carbonic Acid

Carbonic acid, H_2CO_3, has a degree of ionization of approximately 1%. Like acetic acid, this low degree of ionization characterizes it as a weak acid.

Evaluate Chlorous Acid

Chlorous acid, HClO_2, also ionizes around 1% as given. Hence, it is classified as a weak acid due to its partial ionization in water.

Evaluate Chloric Acid

Chloric acid, HClO_3, ionizes at about 100% in solution. A complete ionization (100%) indicates that chloric acid is a strong acid, as it fully dissociates into ions in aqueous solution.

Key concepts

Acid Strength

Acid strength refers to the ability of an acid to dissociate into its ions in an aqueous solution. When we talk about acid strength, we're essentially discussing how completely an acid releases its hydrogen ions (H⁺) in water.
Acids can be classified as strong or weak based on their ionization level:

• Strong acids: These acids dissociate completely in water, releasing all of their hydrogen ions. This means they undergo a complete ionization process, resulting in nearly 100% dissociation. Examples include hydrochloric acid (HCl) and sulfuric acid (H₂SO₄).
• Weak acids: These acids only partially dissociate in water, meaning not all of their molecules release hydrogen ions completely. Their ionization percentage is much less than 100%. Examples include acetic acid (HC₂H₃O₂) and carbonic acid (H₂CO₃).

Ionization Degree

The degree of ionization of an acid refers to the percentage of ionization when dissolved in water. This concept dictates how strong or weak an acid is in solution. Let's simplify it:

• If an acid has a high degree of ionization (close to 100%), it is considered a strong acid. These acids fully break down into ions, leaving few or no acidic molecules in their undissociated form.
• If an acid has a low degree of ionization (much less than 100%), it is classified as a weak acid. In this case, most of the acid molecules remain intact without releasing H⁺ ions.

For example, chloric acid (HClO₃) with nearly 100% ionization is a strong acid, while acetic acid (HC₂H₃O₂) with about 1% ionization is weak.

Strong Acids

Strong acids are typically characterized by their ability to completely ionize in solution. This means that they almost entirely dissociate into their constituent ions when dissolved in water. These acids significantly raise the hydrogen ion concentration, making the solution very acidic.
Some notable characteristics of strong acids include:

• They have high conductivity in water due to the presence of a large number of ions.
• They generally have a low pH value, often less than 3.
• They're often used in industrial and laboratory settings due to their effective and predictable reactions.

Chloric acid (HClO₃), which ionizes almost completely, serves as an example of a strong acid.
This complete ionization results in a swift and powerful interaction in chemical reactions.

Weak Acids

Weak acids are those acids that do not fully dissociate in water, resulting in a relatively low concentration of hydrogen ions in solution. This partial ionization means that a significant portion of the acid remains in the form of undissociated molecules.
Here are some important points about weak acids:

• They have a relatively higher pH compared to strong acids, typically between 3 and 7.
• Their solutions are less conductive due to fewer free ions.
• They're commonly found in biological systems and everyday products, such as vinegar (which contains acetic acid).

Acids like acetic acid (HC₂H₃O₂) and carbonic acid (H₂CO₃) exhibit a low degree of ionization, around 1%, making them classic examples of weak acids.
Understanding weak acids is crucial for those studying reactions where precise control over acidity is necessary.