Problem 2 - Chemistry and Chemical Reactivity

Question

Write the formula and give the name of the conjugate acid of each of the following bases. (a) \(\mathrm{NH}_{3}\) (b) \(\mathrm{HCO}_{3}^{-}\) (c) \(\mathrm{Br}^{-}\)

Step-by-Step Solution

Answer

NH₃ → NH₄⁺; HCO₃⁻ → H₂CO₃; Br⁻ → HBr.

Step 1: Understanding Conjugate Acids

To find the conjugate acid of a base, add a hydrogen ion (H⁺) to the base. This is because when a base accepts a proton, it becomes a conjugate acid.

Step 2: Finding the Conjugate Acid of NH3

The base, \(NH_{3}\), accepts a proton to become \(NH_{4}^{+}\). Thus, the conjugate acid of ammonia (NH₃) is ammonium (NH₄⁺).

Step 3: Finding the Conjugate Acid of HCO3^-

The base, \(HCO_{3}^{-}\), accepts a proton to become \(H_{2}CO_{3}\). Thus, the conjugate acid of bicarbonate (HCO₃⁻) is carbonic acid (H₂CO₃).

Step 4: Finding the Conjugate Acid of Br^-

The base, \(Br^{-}\), accepts a proton to become \(HBr\). Thus, the conjugate acid of bromide (Br⁻) is hydrobromic acid (HBr).

Key Concepts

Conjugate Acids

In acid-base chemistry, understanding conjugate acids is essential for comprehending how acids and bases interact. When a base accepts a proton (\(H^+\)), it becomes a conjugate acid. This is a fundamental concept because it explains the behavior of substances in proton transfer reactions.

• For every base, there is a corresponding conjugate acid formed by the addition of a hydrogen ion.
• This concept helps predict the products of acid-base reactions.
• Conjugate acids typically have one more hydrogen atom and a positive charge compared to their base counterparts.

By looking at examples like ammonia (\(NH_3\)), bicarbonate (\(HCO_3^-\)), and bromide (\(Br^-\)), we can see how each base transforms into its conjugate acid upon accepting a proton.

Proton Transfer

Proton transfer is a key mechanism in acid-base reactions, where protons (\(H^+\)) are transferred from one molecule to another. This process is at the heart of reactions between acids and bases. When a proton donor (acid) loses a proton, it turns into its conjugate base. Likewise, when a base gains a proton, it becomes its conjugate acid.

• Proton transfer is what allows acids to release hydrogen ions in a solution.
• The direction of proton transfer typically favors the formation of weaker acids and bases.
• This process is reversible, as conjugate acids and bases can convert back to their parent acids and bases under the right conditions.

Understanding proton transfer allows us to see how different substances can alter pH and interact in chemical environments.

Ammonia and Ammonium

Ammonia (\(NH_3\)) is a common atmospheric gas and a base in acid-base reactions. When it acts as a base, it accepts a proton to form ammonium (\(NH_4^+\)). This protonated form, ammonium, is critical in several chemical reactions and biological systems.

• Ammonia can neutralize acids, forming ionic compounds with various acids.
• As ammonium, it partakes in ammonium chloride production, found in fertilizers.
• The transformation to ammonium is crucial in nitric acid production and nitrogen cycling.

Ammonium, like other conjugate acids, has unique properties that make it vital in different fields, from agriculture to industrial applications.

Bicarbonate and Carbonic Acid

Bicarbonate (\(HCO_3^-\)) acts as a base that can convert to carbonic acid (\(H_2CO_3\)), an essential player in biological and environmental systems. The transition between bicarbonate and carbonic acid exemplifies buffering systems that maintain pH balance in environments such as blood and oceans.

• Bicarbonate is part of the main buffer system in the human bloodstream.
• Carbonic acid stabilizes pH by breaking down into water and carbon dioxide.
• This acid-base pairing is crucial in respiratory and metabolic acid-base control.

Understanding the bicarbonate-carbonic acid system is fundamental in studying physiological responses to changes in pH and the broader carbon cycle.

Bromide and Hydrobromic Acid

Bromide (\(Br^-\)) is an anion that can be protonated to form hydrobromic acid (\(HBr\)), a strong acid. This transformation is significant in industrial chemistry, aesthetics, and synthetic procedures.

• Hydrobromic acid is used in the production of bromine compounds.
• As a strong acid, it completely dissociates in water, making it effective in pH adjustment.
• Its strength allows it to participate in the synthesis of alkyl bromides.

The conversion of bromide to hydrobromic acid illustrates the transition from a neutral, ionic form to a highly active and influential chemical compound.