key term - Weaker base

Definition

A weaker base is a substance that has a lower tendency to accept protons compared to stronger bases, resulting in a lower pH when dissolved in water. Weaker bases typically dissociate less completely in solution, leading to a smaller concentration of hydroxide ions ($$OH^-$$) than stronger bases. This property is crucial when considering acid-base reactions and the formation of acid-base conjugate pairs.

5 Must Know Facts For Your Next Test

1. Weaker bases have higher pKa values compared to stronger bases, indicating their lower proton-accepting ability.
2. In water, weaker bases will produce fewer hydroxide ions than stronger bases, leading to higher equilibrium concentrations of their conjugate acids.
3. Examples of weaker bases include ammonia (NH3) and bicarbonate (HCO3-), which only partially ionize in solution.
4. The strength of a base can be influenced by its molecular structure, such as the presence of electronegative atoms or resonance stabilization.
5. Understanding weaker bases is essential for predicting the direction of acid-base reactions and the stability of conjugate pairs.

Review Questions

• How does the concept of a weaker base relate to the strength of its conjugate acid?
  • The strength of a weaker base is closely tied to the strength of its conjugate acid. When a weak base accepts a proton, it forms its conjugate acid, which will be a stronger acid due to its ability to donate protons more readily. This inverse relationship means that as the base becomes weaker, its conjugate acid tends to be stronger, reflecting the balance in the acid-base equilibrium.
• Discuss how the dissociation of weaker bases differs from that of strong bases in terms of pH and hydroxide ion concentration.
  • Weaker bases do not dissociate completely in solution like strong bases do. As a result, they produce fewer hydroxide ions ($$OH^-$$), which leads to a higher pH compared to solutions with strong bases. The incomplete dissociation means that at equilibrium, there are more undissociated molecules of the weak base remaining, leading to lower overall alkalinity than what is observed with strong bases that fully dissociate and generate large amounts of hydroxide ions.
• Evaluate how molecular structure influences the basicity of substances and their classification as weaker or stronger bases.
  • The basicity of substances can significantly be influenced by their molecular structure. For example, the presence of electronegative atoms can stabilize the positive charge on the conjugate acid formed when the base accepts a proton. Additionally, resonance structures can also play a role by distributing charge over multiple atoms. Consequently, molecules with structures that allow for such stabilization tend to be stronger bases, while those lacking these features are classified as weaker bases due to their lower tendency to accept protons effectively.

Related terms

strong base:

A strong base is a substance that completely dissociates in water to yield hydroxide ions, resulting in a higher pH and a greater ability to accept protons.

Brønsted-Lowry acid: A Brønsted-Lowry acid is a substance that donates protons (H+) during a chemical reaction, playing a key role in defining acid-base interactions.

conjugate acid-base pair:

A conjugate acid-base pair consists of two species that transform into each other by the gain or loss of a proton, showcasing the relationship between acids and bases.