Question

In an \(\mathrm{H}_{2} \mathrm{CO}_{3}\) molecule, both hydrogen atoms are bonded to oxygen atoms. How many acidic hydrogen atoms does carbonic acid have?

Short answer

Carbonic acid (\( \mathrm{H}_{2} \mathrm{CO}_{3}\)) has two acidic hydrogens.

Step-by-step solution

Understand Acidic Hydrogen

An acidic hydrogen is a hydrogen atom that is part of an acid molecule that can be donated to a base. In the Brnsted-Lowry definition of acids and bases, an acid is a proton (H+) donor, and a base is a proton (H+) acceptor.

Determine the Molecular Structure of Carbonic Acid

The molecule of carbonic acid (H2CO3) consists of two hydrogen atoms, one carbon atom, and three oxygen atoms. Both of the hydrogen atoms are bonded to the same oxygen atom.

Count the Acidic Hydrogens

In carbonic acid, both of the hydrogen atoms are capable of being donated to a base, making them acidic hydrogens. Therefore, carbonic acid has two acidic hydrogens.

Key concepts

Carbonic Acid

Carbonic acid, represented chemically as \( \mathrm{H}_2\mathrm{CO}_3 \), plays a vital role in various biological and environmental systems. It forms when carbon dioxide (\( \mathrm{CO}_2 \)) dissolves in water and interacts with water molecules. This reaction is crucial in maintaining pH balance in blood and is part of the global carbon cycle.

Carbonic acid is a weak acid, meaning it doesn't ionize completely in water. Understanding carbonic acid is essential because it is involved in processes like respiration and photosynthesis. When carbonic acid dissociates, it releases hydrogen ions, which can impact the acidity of solutions.

• Structure: \( \mathrm{H}_2\mathrm{CO}_3 \)
• Formation: Dissolution of \( \mathrm{CO}_2 \) in water.
• Role: pH regulation and carbon cycle.

Brønsted-Lowry Definition

The Brønsted-Lowry definition is a fundamental principle in acid-base chemistry. This concept, introduced by Johannes Brønsted and Thomas Lowry in 1923, describes acids and bases differently from traditional definitions. According to Brønsted-Lowry, an acid is a substance that donates a proton (\( \mathrm{H}^+ \)) to another substance, while a base is a substance that accepts a proton.

This definition is broader than the Arrhenius concept, allowing it to explain behavior in non-aqueous environments as well. For instance, when carbonic acid (\( \mathrm{H}_2\mathrm{CO}_3 \)) donates a proton, it acts as a Brønsted-Lowry acid, and the species accepting this proton acts as a Brønsted-Lowry base.

• Acid: Proton donor.
• Base: Proton acceptor.
• Flexibility: Applicable in various environments.

Proton Donor

A proton donor is a key concept connected to acids in the Brønsted-Lowry theory. In the context of carbonic acid, the molecule can donate its hydrogen ions (protons) to bases in chemical reactions. This ability to release \( \mathrm{H}^+ \) ions defines its acidic property.

In \( \mathrm{H}_2\mathrm{CO}_3 \), each hydrogen atom is linked to an oxygen atom, making them potential donors. When carbonic acid acts as a proton donor, it typically forms bicarbonate (\( \mathrm{HCO}_3^- \)) or carbonate ions (\( \mathrm{CO}_3^{2-} \)), depending on how many protons have been donated.

• Proton: \( \mathrm{H}^+ \)
• Product: Bicarbonate or carbonate ions.
• Importance: Central to acid functionality.

Molecular Structure

Understanding the molecular structure of carbonic acid can provide insight into its chemical behavior and properties. Carbonic acid (\( \mathrm{H}_2\mathrm{CO}_3 \)) consists of:

• Two hydrogen atoms
• One carbon atom
• Three oxygen atoms

In its structure, the hydrogen atoms are each bonded to an oxygen atom within the molecule, contributing to its capability as a proton donor. Generally, the connectivity looks like this: each \( \mathrm{H} \) is attached to \( \mathrm{O} \), with the central carbon atom bonded to three oxygen atoms, one of which forms a double bond.

This molecular setup not only helps recognize the proton donor capabilities of carbonic acid but also emphasizes its overall shape and stability as a molecule. Such structural knowledge is crucial for understanding how molecules interact in more complex chemical systems.