Question

State whether each of the following substances in an aqueous solution is highly ionized or slightly ionized: (a) weak acids (b) weak bases (c) slightly soluble ionic compounds

Short answer

Weak acids, weak bases, and slightly soluble ionic compounds are slightly ionized in aqueous solutions.

Step-by-step solution

Understanding Ionization

Ionization in aqueous solutions refers to the process where a substance separates into ions. This process varies depending on whether the substance is a strong electrolyte, weak electrolyte, or non-electrolyte.

Analyzing Weak Acids

Weak acids are substances that do not completely ionize in solution. Only a small fraction of acid molecules donate protons to form ions, which means they are slightly ionized in water.

Analyzing Weak Bases

Similar to weak acids, weak bases do not fully dissociate into ions in solution. They partially ionize, meaning they are slightly ionized in aqueous solutions.

Considering Slightly Soluble Ionic Compounds

Slightly soluble ionic compounds dissolve minimally in water. The extent of ionization is limited by their low solubility, resulting in these compounds being slightly ionized.

Key concepts

Weak Acids

Weak acids are fascinating substances in chemistry because, unlike strong acids, they do not fully dissociate into their ions when dissolved in water. This incomplete dissociation means that only a small proportion of the acid molecules release their protons (H⁺ ions) into the solution. This limited ionization is what characterizes them as "weak."
To understand why weak acids are slightly ionized, consider acetic acid, a common weak acid found in vinegar:

• Acetic acid ({CH₃COOH}) only partially releases H⁺ ions, forming acetate ions and hydrogen ions in water.
• The majority of the acetic acid molecules remain intact and do not ionize.

This behavior is due to the equilibrium that weak acids maintain between their ionized and non-ionized forms. The acid dissociation constant, denoted as Ka, quantifies the strength of a weak acid, with smaller values indicating weaker acids.
In essence, when you dissolve a weak acid in water, you end up with a mixture predominantly containing non-ionized acid molecules along with a small number of ions.

Weak Bases

Weak bases, much like weak acids, are characterized by their partial ionization in water. They do not fully dissociate into ions, which is why they are also considered to be slightly ionized. An example of a weak base is ammonia ({NH₃}), commonly used in cleaning products.
When dissolved in water, ammonia reacts with water molecules to form a limited amount of ammonium ions ({NH₄⁺}) and hydroxide ions ({OH⁻}):

• This reaction is reversible, meaning that not all ammonia molecules will ionize at once.
• The degree of ionization is relatively small, resulting in a solution that is only slightly basic.

Just as weak acids have an acid dissociation constant ({Ka}), weak bases have a base dissociation constant ({Kb}) that measures their strength. Smaller {Kb} values indicate weaker bases, reflecting their reduced ionization capacity.
Ultimately, weak bases offer an intriguing look into how molecules interact in water and demonstrate how ionization varies across different substances.

Slightly Soluble Ionic Compounds

Slightly soluble ionic compounds introduce an interesting concept in the world of chemistry. Unlike highly soluble salts, these substances dissolve minimally in water, leading to limited ionization. The solubility product constant, known as {Ksp}, serves as a measure for the solubility of these compounds.
An excellent example to illustrate this concept is calcium sulfate ({CaSO₄}):

• In water, {CaSO₄} only dissolves slightly to release calcium ions ({Ca²⁺}) and sulfate ions ({SO₄²⁻}).
• Most of the compound remains undissolved in solid form.

The small degree of ionization is dictated by the {Ksp} value, which is often very low for slightly soluble ionic compounds.
These limited solubility and ionization characteristics make slightly soluble ionic compounds unique, as they behave differently from the more common highly soluble salts that completely dissociate into ions in aqueous solutions.