Arrhenius definition of acids and bases | Biology | Khan Academy

Summary

This script delves into the modern concept of acids and bases, introduced by Svante Arrhenius, a Nobel laureate in Chemistry. It explains that acids increase hydrogen ion concentration in aqueous solutions, exemplified by hydrochloric acid forming hydronium ions. Bases, like sodium hydroxide, increase hydroxide concentration, dissociating into sodium ions and hydroxide anions in water. The explanation invites comparison with other definitions of acids and bases, such as the Bronsted-Lowry and Lewis theories.

Takeaways

• 🔬 Svante Arrhenius was the third recipient of the Nobel Prize in Chemistry in 1903 and developed the modern concept of acids and bases.
• 🧪 According to Arrhenius, an acid is a substance that increases the concentration of hydrogen protons (H+) when dissolved in an aqueous solution.
• 💧 A base, under the Arrhenius definition, increases the concentration of hydroxide ions (OH-) when dissolved in an aqueous solution.
• 📈 Hydrochloric acid (HCl) is an example of a strong Arrhenius acid, as it disassociates completely in water to release hydrogen ions and chloride ions.
• 💥 The hydrogen proton released by HCl doesn't exist alone in water; it bonds with a water molecule to form hydronium ions (H3O+).
• ⚡ The strong disassociation of hydrochloric acid in water is what makes it a strong acid by the Arrhenius definition.
• 🧱 Sodium hydroxide (NaOH) is an example of a strong Arrhenius base, as it disassociates completely in water to release sodium ions and hydroxide ions.
• 🔗 Sodium hydroxide has an ionic bond between the sodium ion (Na+) and the hydroxide ion (OH-), which disassociates in water.
• 🌊 When sodium hydroxide is dissolved in water, it increases the hydroxide ion concentration, making it a strong base according to Arrhenius.
• 🧠 The video encourages comparing the Arrhenius definition of acids and bases with the Bronsted-Lowry and Lewis definitions to better understand the categorization of substances.

Q & A

Who introduced the modern conception of acids and bases?

The modern conception of acids and bases was introduced by Svante Arrhenius, who was the third recipient of the Nobel Prize in Chemistry in 1903.

According to Arrhenius, what defines an acid?

According to Arrhenius, an acid is something that increases the concentration of hydrogen protons (H+) when put in an aqueous solution.

How does Arrhenius define a base?

Arrhenius defines a base as something that increases the concentration of hydroxide ions (OH-) when put in an aqueous solution.

What happens when hydrochloric acid (HCl) is put in an aqueous solution?

When hydrochloric acid (HCl) is put in an aqueous solution, it dissociates into hydrogen protons (H+) and chloride ions (Cl-), increasing the concentration of hydrogen ions in the solution.

Why is hydrochloric acid considered a strong acid by the Arrhenius definition?

Hydrochloric acid is considered a strong acid by the Arrhenius definition because it significantly increases the concentration of hydrogen protons (H+) in an aqueous solution.

What happens to hydrogen protons (H+) in water?

In water, hydrogen protons (H+) bond with water molecules to form hydronium ions (H3O+), rather than existing as free protons.

What is the chemical reaction that occurs when hydrochloric acid is dissolved in water?

When hydrochloric acid is dissolved in water, the reaction can be written as: HCl + H2O → H3O+ + Cl-, where HCl dissociates to form hydronium ions (H3O+) and chloride ions (Cl-).

What defines a strong Arrhenius base?

A strong Arrhenius base is defined as a substance that significantly increases the concentration of hydroxide ions (OH-) when dissolved in water.

What happens when sodium hydroxide (NaOH) is dissolved in water?

When sodium hydroxide (NaOH) is dissolved in water, it dissociates into sodium ions (Na+) and hydroxide ions (OH-), increasing the hydroxide ion concentration in the solution.

How does sodium hydroxide (NaOH) bond at the molecular level?

Sodium hydroxide (NaOH) consists of a sodium ion (Na+) that has lost an electron, giving it a positive charge, and a hydroxide ion (OH-) that has a negative charge. These ions are attracted to each other, forming an ionic bond.