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

(a) NH4+ (ammonium), (b) H2CO3 (carbonic acid), (c) HBr (hydrobromic acid).

Step 1: Understand What a Conjugate Acid Is

In Bronsted-Lowry acid-base theory, a conjugate acid is formed when a base gains a proton ( H^+ ). Thus, for each base given, adding an H^+ will give the conjugate acid.

Step 2: Find the Conjugate Acid of NH3

For NH_3 (ammonia), the base accepts a proton ( H^+ ) to form NH_4^+ . The formula for its conjugate acid is therefore NH_4^+ , which is called ammonium.

Step 3: Find the Conjugate Acid of HCO3−

For HCO_3^- (bicarbonate), the base accepts a proton ( H^+ ) to form H_2CO_3 . So the formula for its conjugate acid is H_2CO_3 , which is called carbonic acid.

Step 4: Find the Conjugate Acid of Br−

For Br^- (bromide), the base accepts a proton ( H^+ ) to form HBr . The formula for its conjugate acid is HBr , commonly known as hydrobromic acid.

Key Concepts

Bronsted-Lowry Acid-Base Theory

The Bronsted-Lowry Acid-Base Theory is a fundamental concept in chemistry. It focuses on the role of protons during reactions. According to this theory, acids are proton donors, while bases are proton acceptors. This definition expands upon the classic Arrhenius concept, as it does not require acids and bases to be in aqueous solutions.

In this framework, when an acid donates a proton, it becomes a conjugate base because it is capable of accepting a proton in the reverse reaction. Likewise, when a base accepts a proton, it forms a conjugate acid. For instance, when \( \mathrm{NH}_3 \) (ammonia) accepts a proton, it forms \( \mathrm{NH}_4^+ \), showing its transformation into a conjugate acid. This exchange of protons is central to understanding and predicting the behavior of acids and bases in chemical reactions.

Proton Transfer

Proton transfer is a critical process in acid-base reactions that involves the movement of protons (\( \mathrm{H}^+ \)) from one molecule to another. This process is instantaneous and happens in a split second once the reaction gets underway.

When evaluating whether a chemical species is acting as an acid or base, consider the following:

• An acid will lose or "donate" a proton;
• A base will gain or "accept" a proton.

By looking at how \( \mathrm{NH}_3 \) accepts a proton to become \( \mathrm{NH}_4^+ \), or how bicarbonate (\( \mathrm{HCO}_3^- \)) accepts a proton to form \( \mathrm{H}_2\mathrm{CO}_3 \) (carbonic acid), we see proton transfer in action. Understanding this transfer process helps predict the product of acid-base reactions, which is crucial for solving chemistry problems.

Acid and Base Nomenclature

The naming of acids and bases is governed by specific rules that help to systematically identify them. This structure is vital for scientists, allowing them to communicate chemical information accurately.

Consider ammonia (\( \mathrm{NH}_3 \)). When it accepts a proton, it becomes ammonium (\( \mathrm{NH}_4^+ \)), which is the conjugate acid. Meanwhile, bicarbonate (\( \mathrm{HCO}_3^- \)) becomes carbonic acid (\( \mathrm{H}_2\mathrm{CO}_3 \)) and bromide (\( \mathrm{Br}^- \)) turns into hydrobromic acid (\( \mathrm{HBr} \)) upon accepting a proton.

The names of acids often reflect their anion's name. For example, acids derived from anions ending in "-ide" often use the prefix "hydro-" and an "-ic" ending (e.g., hydrobromic acid from bromide). Understanding the naming conventions helps students correctly interpret chemical names and formulas, fostering a deeper grasp of chemistry concepts at play.