Brønsted–Lowry acids and bases | Chemical reactions | AP Chemistry | Khan Academy

Summary

This video script delves into the formal definition of acids, focusing on the Bronsted-Lowry theory from the 1920s. It explains that an acid is a proton or hydrogen ion donor, while a base is a proton acceptor. Using hydrochloric acid as an example, the script illustrates the acid-base reaction in an aqueous solution, highlighting the formation of hydronium ions from protons and water, and the resulting chloride anions. The explanation clarifies the dual role of water as both an acid and a base, and the concept of conjugate acids and bases.

Takeaways

• 🔬 The video discusses the formal definition of an acid, focusing on the Bronsted-Lowry definition.
• 🌟 An acid, according to Bronsted-Lowry, is a proton (H+) or hydrogen ion donor.
• 💧 A base is defined as a proton (H+) or hydrogen ion acceptor.
• 🧲 The video explains that a proton and a hydrogen ion are essentially the same, especially in the context of the most common hydrogen isotope.
• 🌊 Hydrochloric acid (HCl) is used as an example of a strong acid that readily donates protons in an aqueous solution.
• 💧 The process of HCl donating a proton to a water molecule is detailed, resulting in the formation of hydronium (H3O+) and chloride (Cl-) ions.
• 🔁 Water acts as a base in this reaction, accepting a proton from the acid, and can also act as an acid or base depending on the circumstances.
• 🔄 The reaction of HCl in water is a conjugate reaction, producing the conjugate base (Cl-) and the conjugate acid (H3O+).
• 📚 The video script clarifies that while sometimes hydrogen ions are depicted as free in aqueous solutions, they actually form hydronium ions when combined with water molecules.
• 📖 The script emphasizes the importance of understanding the Bronsted-Lowry definition of acids and bases for a foundational understanding of chemistry.

Q & A

What is the main focus of the video script?

The video script focuses on providing a formal definition of an acid, specifically using the Bronsted-Lowry definition of acids and bases.

Who are Bronsted and Lowry, and what did they contribute to the field of chemistry?

Bronsted and Lowry are chemists who came up with the Bronsted-Lowry definition of acids and bases in the 1920s.

According to the Bronsted-Lowry definition, what is considered an acid?

An acid, according to the Bronsted-Lowry definition, is a proton or hydrogen ion donor.

Why are a proton and a hydrogen ion considered the same thing?

A proton and a hydrogen ion are considered the same because the most common isotope of hydrogen consists of just a proton in its nucleus with no neutron, and when ionized, it loses its electron, leaving only the proton.

What is the role of a base in the Bronsted-Lowry definition?

A base, in the Bronsted-Lowry definition, is a proton or hydrogen ion acceptor.

Can you provide an example of a strong acid mentioned in the script?

Hydrochloric acid (HCl) is an example of a strong acid mentioned in the script.

What happens when hydrochloric acid is placed in an aqueous solution?

In an aqueous solution, hydrochloric acid donates a proton to a water molecule, forming a chloride anion and a hydronium ion.

What is the role of water in the reaction involving hydrochloric acid in an aqueous solution?

In the reaction, water acts as a base by accepting a proton from the hydrochloric acid, forming a hydronium ion.

What are the products of the reaction when hydrochloric acid is dissolved in water?

The products of the reaction are chloride anions and hydronium ions.

What are conjugate acid-base pairs in the context of the reaction described in the script?

The conjugate acid-base pairs in the reaction are the chloride anion (conjugate base of hydrochloric acid) and the hydronium ion (conjugate acid of water).

Why do the protons in an aqueous solution not exist by themselves?

Protons in an aqueous solution do not exist by themselves because they are immediately grabbed by a water molecule to form hydronium ions.

How does the script clarify the dual nature of water as both an acid and a base?

The script clarifies that water can act as both an acid and a base by accepting a proton from hydrochloric acid (acting as a base) and also being able to donate protons under the right circumstances (acting as an acid).