Problem 89
Question
Are all Arrhenius bases also Bronsted-Lowry bases? Are \(15.9=\) all Bronsted-Lowry bases also Arrhenius bases? If yes, explain why. If not, give a specific example to demonstrate the difference.
Step-by-Step Solution
Verified Answer
Answer: All Arrhenius bases are Bronsted-Lowry bases, but not all Bronsted-Lowry bases are Arrhenius bases.
1Step 1: Define an Arrhenius base
An Arrhenius base is a substance that increases the concentration of hydroxide ions (OH-) in aqueous solution when dissolved.
2Step 2: Define a Bronsted-Lowry base
A Bronsted-Lowry base is a substance that can accept a proton (H+) from another substance in a chemical reaction.
3Step 3: Compare Arrhenius bases to Bronsted-Lowry bases
All Arrhenius bases are Bronsted-Lowry bases because they increase the concentration of OH- ions in solution by accepting a proton (H+) from water to form hydroxide ions. Since the process of accepting a proton is a defining characteristic of a Bronsted-Lowry base, all Arrhenius bases satisfy this requirement.
4Step 4: Compare Bronsted-Lowry bases to Arrhenius bases
Not all Bronsted-Lowry bases are Arrhenius bases. Bronsted-Lowry bases encompass a wider variety of substances, since their definition only requires the ability to accept a proton. An Arrhenius base, on the other hand, specifically increases the concentration of hydroxide ions in the solution. Thus, some Bronsted-Lowry bases do not meet the criteria for being an Arrhenius base.
5Step 5: Provide an example of a Bronsted-Lowry base not being an Arrhenius base
An example of a Bronsted-Lowry base that is not an Arrhenius base is ammonia (NH3). When ammonia is added to water, it accepts a proton (H+) from water forming the ammonium ion (NH4+) and a hydroxide ion (OH-). The chemical reaction can be represented as:
NH3 + H2O -> NH4+ + OH-
In this case, ammonia is a Bronsted-Lowry base because it accepts a proton from water. However, it is not an Arrhenius base because it does not directly introduce hydroxide ions into the solution (rather, these are a product of its reaction with water).
Key Concepts
Arrhenius BasesBronsted-Lowry BasesAmmonia NH3 as a Base
Arrhenius Bases
Arrhenius bases are defined by their ability to increase the concentration of hydroxide ions (OH⁻) in water.
This happens when they dissolve in water and separate into ions.
For example:
Therefore, Arrhenius bases typically contain hydroxide in their formula.
It's important to note that this results in a basic or alkaline solution with a pH greater than 7.
Additionally, the Arrhenius definition mainly applies to aqueous solutions.
This happens when they dissolve in water and separate into ions.
For example:
- Sodium hydroxide (NaOH) dissolves in water to give hydroxide ions and sodium ions.
- Potassium hydroxide (KOH) does the same, adding OH⁻ ions to the solution.
Therefore, Arrhenius bases typically contain hydroxide in their formula.
It's important to note that this results in a basic or alkaline solution with a pH greater than 7.
Additionally, the Arrhenius definition mainly applies to aqueous solutions.
Bronsted-Lowry Bases
The concept of Bronsted-Lowry bases broadens the scope of bases beyond the Arrhenius definition.
According to Bronsted-Lowry theory, a base is any substance capable of accepting a proton (H⁺) from another substance.
This definition doesn't require the direct release of OH⁻ ions.
Some examples include:
It includes not only aqueous solutions but also reactions in non-aqueous environments.
According to Bronsted-Lowry theory, a base is any substance capable of accepting a proton (H⁺) from another substance.
This definition doesn't require the direct release of OH⁻ ions.
Some examples include:
- Ammonia (NH₃), which accepts protons from water to form ammonium (NH₄⁺) and OH⁻.
- Acetate ion (CH₃COO⁻), which can accept a proton to form acetic acid (CH₃COOH).
It includes not only aqueous solutions but also reactions in non-aqueous environments.
Ammonia NH3 as a Base
Ammonia (NH₃) is a classic example of a Bronsted-Lowry base that does not fit the Arrhenius definition.
When ammonia is added to water, it accepts a proton from water to form ammonium ions (NH₄⁺) and releases hydroxide ions (OH⁻):\[\text{NH}_3 + \text{H}_2\text{O} \rightarrow \text{NH}_4^+ + \text{OH}^-\]This reaction allows ammonia to act as a base by increasing the concentration of OH⁻ ions, but not in the direct manner of an Arrhenius base.
Here are some key points about ammonia's behavior:
When ammonia is added to water, it accepts a proton from water to form ammonium ions (NH₄⁺) and releases hydroxide ions (OH⁻):\[\text{NH}_3 + \text{H}_2\text{O} \rightarrow \text{NH}_4^+ + \text{OH}^-\]This reaction allows ammonia to act as a base by increasing the concentration of OH⁻ ions, but not in the direct manner of an Arrhenius base.
Here are some key points about ammonia's behavior:
- Ammonia's ability to accept protons makes it an excellent Bronsted-Lowry base.
- Its indirect production of OH⁻ ions through interaction with water distinguishes it from most Arrhenius bases.
- Due to its gaseous state at room temperature, it can enter into reactions easily in aqueous and gaseous forms.
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