Problem 5 - Chemistry and Chemical Reactivity

Question

Write balanced equations showing how the hydrogen oxalate ion, \(\mathrm{HC}_{2} \mathrm{O}_{4}^{-},\) can be both a Bronsted acid and a Bronsted base.

Step-by-Step Solution

Answer

Hydrogen oxalate can donate a proton to become \(\text{C}_2\text{O}_4^{2-}\) or accept a proton to become \(\text{H}_2\text{C}_2\text{O}_4\).

Step 1: Understanding Hydrogen Oxalate as a Bronsted Acid

As a Bronsted acid, the hydrogen oxalate ion, \( ext{HC}_2 ext{O}_4^-\), donates a proton (\( ext{H}^+\)) to become \( ext{C}_2 ext{O}_4^{2-}\). The balanced equation for this reaction is: \[ ext{HC}_2 ext{O}_4^- ightarrow ext{H}^+ + ext{C}_2 ext{O}_4^{2-}\] This shows hydrogen oxalate acting as a proton donor.

Step 2: Understanding Hydrogen Oxalate as a Bronsted Base

As a Bronsted base, the hydrogen oxalate ion, \( ext{HC}_2 ext{O}_4^-\), accepts a proton, becoming \( ext{H}_2 ext{C}_2 ext{O}_4\). The balanced equation for this reaction is: \[ ext{HC}_2 ext{O}_4^- + ext{H}^+ ightarrow ext{H}_2 ext{C}_2 ext{O}_4\] This demonstrates hydrogen oxalate acting as a proton acceptor.

Key Concepts

Hydrogen Oxalate Ion

The hydrogen oxalate ion, represented as \(\mathrm{HC}_2 \mathrm{O}_4^{-}\), is an interesting chemical species that plays an important role in acid-base chemistry.
It is derived from oxalic acid, which contains two carboxylic acid groups capable of releasing hydrogen ions (protons). When one of these protons is removed, the result is the hydrogen oxalate ion.
This ion is unique because it can act as either an acid or a base, depending on the surrounding conditions. This dual behavior is part of what makes it an amphoteric substance.
In the context of Bronsted-Lowry acid-base theory, the hydrogen oxalate ion can lose a proton to become the oxalate ion (\(\mathrm{C}_2 \mathrm{O}_4^{2-}\)) or gain a proton to form oxalic acid (\(\mathrm{H}_2\mathrm{C}_2\mathrm{O}_4\)).
The ability to either donate or accept protons is central to many chemical and biological processes, making the study of ions like hydrogen oxalate crucial for students studying chemistry. As part of the Bronsted acid-base pair, it shows how substances can interconvert under different chemical conditions.

Proton Donor

In the world of chemistry, a proton donor is a substance that can donate a proton, which is a hydrogen ion (\(\mathrm{H}^+\)).
In the Bronsted-Lowry acid-base theory, acids are defined primarily by their ability to donate protons.
When the hydrogen oxalate ion \(\mathrm{HC}_2 \mathrm{O}_4^{-}\) acts as an acid, it donates a proton and transforms into the oxalate ion \(\mathrm{C}_2 \mathrm{O}_4^{2-}\).
This reaction can be represented by the equation:
\[\mathrm{HC}_2 \mathrm{O}_4^{-} \rightarrow \mathrm{H}^+ + \mathrm{C}_2 \mathrm{O}_4^{2-}\]
- **Key Points:**
- Donating a proton means reducing the hydrogen content of the molecule.
- This process can affect the pH of the surroundings, making it more alkaline.
- Understanding proton donors is crucial for grasping how acids behave under the Bronsted acid-base theory.
Recognizing substances like the hydrogen oxalate ion in their proton-donating state is essential for predicting chemical reactions and for broader chemical knowledge.

Proton Acceptor

Conversely, a proton acceptor is a substance that can accept protons, emphasizing its role in basic chemical reactions.
Under the Bronsted-Lowry acid-base theory, bases are characterized by their ability to accept protons.
When hydrogen oxalate ion \(\mathrm{HC}_2 \mathrm{O}_4^{-}\) behaves as a base, it accepts an additional proton (\(\mathrm{H}^+\)), forming oxalic acid \(\mathrm{H}_2\mathrm{C}_2\mathrm{O}_4\).
This transformation can be shown by the equation:
\[\mathrm{HC}_2 \mathrm{O}_4^{-} + \mathrm{H}^+ \rightarrow \mathrm{H}_2\mathrm{C}_2\mathrm{O}_4\]
- **Key Points:**
- Accepting a proton adds to the hydrogen content of the molecule.
- This can make the surroundings more acidic.
- Understanding proton acceptors is as fundamental as grasping proton donors in the study of Bronsted acids and bases.
Comprehending how substances like the hydrogen oxalate ion interact in their proton-accepting capacities allows students to predict and understand various chemical reactions and behaviors effectively.