What Is The Bronsted Lowry Theory | Acids, Bases & Alkali's | Chemistry | FuseSchool

Summary

The Bronsted-Lowry theory expands upon the Arrhenius theory by redefining acids and bases. Acids are now substances that donate H+ ions, while bases are those that accept these ions. This theory explains how ammonia can act as a base without releasing OH- ions, as it accepts H+ from water. Water is identified as amphoteric, capable of acting as both an acid and a base, depending on the reaction. The essence of an acid-base reaction, according to Bronsted-Lowry, is the transfer of a proton (H+).

Takeaways

• 📚 The Arrhenius theory defines acids as substances releasing H+ ions and bases as those releasing OH- ions in solution.
• 🌟 Ammonia (NH3) can act as a base despite not containing OH- ions, challenging the Arrhenius definition.
• 📈 The Bronsted-Lowry theory expands on the Arrhenius theory, focusing on the transfer of H+ ions rather than just their release.
• 🔍 Acids can be detected using universal indicator solutions or papers, which change color based on the acid's strength.
• 💧 In the presence of acids, blue litmus paper turns red, indicating acidity.
• 🌊 Hydrochloric acid (HCl) is an example of an acid, formed when hydrogen chloride gas dissolves in water and dissociates into H+ and Cl- ions.
• 🔄 The H+ ion from HCl transfers to water, forming a hydronium ion (H3O+), also known as an oxonium ion.
• 📌 A Bronsted-Lowry acid donates H+ ions, while a Bronsted-Lowry base accepts them, regardless of pH levels.
• 🤔 Ammonia acts as a base by accepting a H+ ion from water, resulting in the formation of NH4+ and OH- ions.
• 🦈 Water is amphoteric, meaning it can act as both an acid and a base, depending on the reaction.
• 🎯 The essence of an acid-base reaction according to the Bronsted-Lowry theory is the transfer of a proton (H+ ion).

Q & A

What is the main difference between the Arrhenius and Bronsted-Lowry theories of acids and bases?

The Arrhenius theory defines acids as substances that release H+ ions and bases as those that release OH- ions in solution, while the Bronsted-Lowry theory broadens the definition to acids as proton (H+) donors and bases as proton acceptors, regardless of their nature or the presence of H+ or OH- ions.

How does the Bronsted-Lowry theory explain the behavior of ammonia as a base despite not containing OH- ions?

According to the Bronsted-Lowry theory, ammonia acts as a base because it accepts a H+ ion from water, forming NH4+ and releasing OH- as a result of the proton transfer.

What is the significance of the hydronium ion (H3O+) in the context of acid dissociation?

The hydronium ion represents the state where a hydrogen ion (H+) has been transferred to water. In the case of hydrochloric acid dissolving in water, HCl dissociates to form H3O+ and Cl-, where H3O+ is the hydronium ion.

How does the pH level relate to the Arrhenius theory of acids?

In the Arrhenius theory, acids are associated with a pH lower than 7 because they release H+ ions, which lower the pH of the solution.

What is an example of an acid that can be identified using a universal indicator solution or paper?

Hydrochloric acid is an example that can be identified by its ability to turn universal indicator solution red or orange, depending on its strength.

How does the Bronsted-Lowry theory expand the definition of acids and bases compared to the Arrhenius theory?

The Bronsted-Lowry theory allows for a broader definition by focusing on the transfer of protons (H+) rather than the specific release of H+ or OH- ions, thus including reactions where no OH- ions are present.

What is the role of water in the acid-base reaction between ammonia and HCl?

Water acts as a Bronsted-Lowry acid in this reaction by releasing a H+ ion that ammonia accepts, forming NH4+ and OH-.

What term describes substances that can act as either an acid or a base?

Amphiprotic substances can act as either an acid or a base, depending on the reaction context.

How does the concept of amphoteric substances relate to the Bronsted-Lowry theory?

Amphiprotic substances, like water, can both donate and accept protons, thus acting as acids or bases in different reactions according to the Bronsted-Lowry theory.

What is the key aspect of an acid-base reaction according to the Bronsted-Lowry theory?

The key aspect is the transfer of a proton (H+) from one substance to another.

How does the Bronsted-Lowry theory help explain the behavior of substances in acid-base reactions?

It provides a more comprehensive understanding by focusing on the transfer of protons, allowing for the classification of reactions that do not strictly follow the Arrhenius definition of releasing H+ or OH- ions.

What is the significance of the universal indicator solution or paper in identifying acids?

The universal indicator solution or paper changes color in the presence of an acid, indicating its strength by turning red or orange, which helps in identifying and classifying acids.

Outlines

00:00

📚 Introduction to Acids and Bases: The Arrhenius and Bronsted-Lowry Theories

This paragraph introduces the viewer to the fundamental concepts of acids and bases according to the Arrhenius theory, which defines acids as substances releasing H+ ions and bases as those releasing OH- ions in solution. It presents the anomaly of ammonia acting as a base without containing OH- ions, setting the stage for the explanation of the Bronsted-Lowry theory. This theory extends the definition of acids and bases to include any substance that donates or accepts H+ ions, respectively, and is not limited by pH levels. The paragraph also explains how acids can be detected using indicators and provides the example of hydrochloric acid, detailing its dissociation in water to form H3O+ and Cl- ions.

Keywords

💡Arrhenius theory

The Arrhenius theory defines acids as substances that release H+ ions and bases as those that release OH- ions in solution. This theory is foundational in understanding the basic properties of acidic and basic solutions. However, it has limitations, as it does not account for substances like ammonia that act as bases without releasing OH- ions, prompting the introduction of the Bronsted-Lowry theory.

💡Bronsted-Lowry theory

The Bronsted-Lowry theory expands upon the Arrhenius theory by redefining acids and bases. An acid is now considered a substance that donates a proton (H+), and a base is one that accepts a proton. This theory allows for a broader understanding of acid-base reactions, including those involving substances that do not contain OH- ions, such as ammonia.

💡Ammonia

Ammonia (NH3) is a compound that, despite not containing OH- ions, can act as a base in the context of the Bronsted-Lowry theory. It does so by accepting a H+ ion from another substance, such as water, in an acid-base reaction. This behavior of ammonia demonstrates the flexibility of the Bronsted-Lowry theory in explaining acid-base reactions beyond the Arrhenius definition.

💡pH

pH is a measure of the hydrogen ion concentration in a solution, which is used to determine its acidity or alkalinity. A pH lower than 7 indicates an acidic solution, while a pH higher than 7 indicates a basic or alkaline solution. The concept of pH is important in the context of the Arrhenius theory, as it is used to identify acids, but the Bronsted-Lowry theory emphasizes the transfer of protons rather than pH levels.

💡Universal indicator

A universal indicator is a chemical that changes color in response to the pH level of a solution. It is used to test the acidity or alkalinity of a substance by observing the color change when the indicator comes into contact with the solution. This tool is particularly useful for demonstrating the properties of acids and their strength.

💡Hydrochloric acid

Hydrochloric acid is a strong acid formed when hydrogen chloride (HCl) gas dissolves in water. In the context of the Arrhenius theory, it is an acid because it releases H+ ions when dissociated in water. The Bronsted-Lowry theory further explains that HCl acts as an acid by donating a proton (H+) to another substance, such as water, forming H3O+ (hydronium ion) and Cl- ions.

💡Hydronium ion

The hydronium ion (H3O+) is a product of the reaction between water and a hydrogen ion (H+). It is formed when water accepts a proton, and it is also known as an oxonium ion. The concept of the hydronium ion is important in the context of the Bronsted-Lowry theory, as it illustrates how water can act as both an acid and a base, depending on the reaction.

💡Acid-base reaction

An acid-base reaction involves the transfer of a proton (H+) from one substance to another. This concept is central to the Bronsted-Lowry theory, which focuses on the behavior of protons rather than the traditional definition of acids and bases based on their pH or the presence of OH- ions.

💡Proton transfer

Proton transfer refers to the process of an acid donating a proton (H+) to a base in an acid-base reaction. This is the fundamental process described by the Bronsted-Lowry theory, which emphasizes the movement of protons rather than the traditional definitions of acids and bases.

💡Amphibian

In the context of the script, 'amphibian' is used metaphorically to describe substances that can act as both acids and bases, similar to how frogs, which are amphibians, can live in both land and water. This term helps to remember and understand the concept of amphoteric substances.

💡Litmus paper

Litmus paper is a type of pH indicator that changes color in the presence of an acidic or basic solution. Red litmus paper turns blue in the presence of a base, while blue litmus paper turns red in the presence of an acid. This tool is used to visually identify the acidic or basic nature of a solution.

Highlights

The Arrhenius theory defines acids as substances releasing H+ ions and bases as those releasing OH- ions in solution.

Ammonia (NH3) can act as a base despite not containing OH- ions, challenging the Arrhenius theory.

The Bronsted-Lowry theory expands upon the Arrhenius theory by not requiring the release of specific ions, focusing instead on the transfer of H+ ions.

Acids are not just released but transferred to another substance, as seen with HCl forming H3O+ (aq) and Cl- (aq) in water.

Water can act as both an acid and a base, depending on the reaction, demonstrating its amphoteric nature.

Ammonia accepts a H+ ion from water, forming NH4+(aq) and OH-(aq), showing its basic nature according to the Bronsted-Lowry theory.

In the Bronsted-Lowry theory, the definition of an acid or base is not dependent on pH levels.

The key requirement for a base in the Bronsted-Lowry theory is the ability to accept H+ ions.

An acid-base reaction, according to the Bronsted-Lowry theory, involves the transfer of a proton (H+ ion).

The universal indicator solution or paper changes color to indicate the presence and strength of an acid.

Blue litmus paper turns red in the presence of an acid, indicating its acidic nature.

Hydrochloric acid is a common example of an acid, formed when hydrogen chloride dissolves in water.

H2O can form a hydronium ion (H3O+) by accepting a H+ ion from HCl.

The Bronsted-Lowry acid is any substance that releases or donates H+ ions in solution.

The Bronsted-Lowry base is any substance that accepts H+ ions in solution.

Amphoteric substances can act as either an acid or a base, similar to how amphibians live in both land and water.

The concept of amphoteric substances bridges the gap between the Arrhenius and Bronsted-Lowry theories of acids and bases.

The final summary encapsulates the essence of the Bronsted-Lowry theory, emphasizing the proton transfer as the core of an acid-base reaction.

Transcripts

The Arrhenius theory of acids and bases defines

an acid as a substance that releases H+ ions in solution, and a base as a substance that

releases OH- ions in solution. We know that ammonia, NH3, can act as a base

and exhibits alkaline properties, but contains no OH- ions. How is this possible?

In this lesson, we will learn about the Bronsted-Lowry theory of acids and bases, which fills in

the gaps in the Arrhenius theory. Knowledge Core

You have learned that acids are substances with a pH lower than 7.

We can test for acids using universal indicator solution or paper, which turns red or orange,

all depending on the strength of the acid. Blue litmus paper also turns red in the presence

of an acid. An example of an acid that you are likely

familiar with is hydrochloric acid. Hydrogen chloride dissolves in water to give

hydrochloric acid. Hydrogen chloride will dissociate to give

a H+ ion and a Cl- ion. HCl --> H+ and Cl-

The H+ ion is not just 'released', but it is transferred to another substance.

HCl(g) + H2O(l) --> H3O+(aq) + Cl-(aq) For our example, water accepts the H+ ion

to form a hydronium ion, H3O+. It is also known as an oxonium ion.

A Bronsted-Lowry acid is a substance that releases or donates H+ ions in solution, in

our case, HCl. A Bronsted-Lowry base is a substance that

accepts H+ ions in solution, in our case, H2O.

Notice that the definition of a Bronsted-Lowry acid or base is not a function of pH.

So an acid-base reaction, according to the Bronsted-Lowry theory, involves the transfer

of a H+ ion from one substance to another. In the introduction, we mentioned that ammonia

acts as a base even though it does not release OH- ions, which is stipulated in the Arrhenius

theory. When ammonia dissolves in water, it accepts

a H+ ion from water. NH3(g) + H2O(l) --> NH4+(aq) + OH-(aq)

Notice that this reaction also involves a H+ ion transfer.

Can you figure out which substance is acting as an acid in this example? Which is acting

as a base? Please pause the lesson to think about this,

and resume when you are ready. In this example, water acts as a Bronsted-Lowry

acid because it releases a H+ ion. Ammonia acts as a Bronsted-Lowry base because

it accepts a H+ ion. A base, according to the Bronsted-Lowry theory,

does not need to have a pH greater than 7 or turn red litmus paper blue, or turn universal

indicator solution or paper blue or purple. The only requirement is that it is able to

accept H+ ions. Have you noticed that H2O acted as a base

in our first example but as an acid in the second example?

Substances that can act as either an acid or a base are amphoteric.

An easy way to remember this term is to recall that frogs are amphibians Ð they live on

land and water. Final Summary

In conclusion, according to the Bronsted-Lowry theory, an acid is a substance that dissociates

to release or donate H+ ions. A Bronsted-Lowry base is a substance that

accepts H+ ions. Therefore, an acid-base reaction, according

to this theory, involves the transfer of a proton.