Question

Give the formula for the conjugate acid of each of the following Bronsted- Lowry bases: (a) \(\mathrm{SO}_{3}^{2-}\) (b) \(\mathrm{H}_{2} \mathrm{O}\) (c) \(\mathrm{CH}_{3} \mathrm{NH}_{2}\) (d) \(\mathrm{OH}\) (e) \(\mathrm{HCO}_{3}^{-}\) (f) \(\mathrm{H}\)

Short answer

(a) \( \mathrm{HSO}_{3}^{-} \); (b) \( \mathrm{H}_{3} \mathrm{O}^{+} \); (c) \( \mathrm{CH}_{3} \mathrm{NH}_{3}^{+} \); (d) \( \mathrm{H}_{2} \mathrm{O} \); (e) \( \mathrm{H}_{2} \mathrm{CO}_{3} \); (f) \( \mathrm{H}^{+} \).

Step-by-step solution

Understanding the Concept of Conjugate Acid

In the Bronsted-Lowry acid-base theory, a conjugate acid is formed when a base gains a proton (H+). It's crucial to identify the base and add an H+ ion to determine the conjugate acid.

Finding the Conjugate Acid for \( \mathrm{SO}_{3}^{2-} \)

To find the conjugate acid of \( \mathrm{SO}_{3}^{2-} \), add an \( \mathrm{H}^+ \) ion. The resulting chemical formula is \( \mathrm{HSO}_{3}^{-} \).

Finding the Conjugate Acid for \( \mathrm{H}_{2} \mathrm{O} \)

Water, \( \mathrm{H}_{2} \mathrm{O} \), acts as a base when it accepts an \( \mathrm{H}^+ \) and thus becomes \( \mathrm{H}_{3} \mathrm{O}^{+} \).

Finding the Conjugate Acid for \( \mathrm{CH}_{3} \mathrm{NH}_{2} \)

The base \( \mathrm{CH}_{3} \mathrm{NH}_{2} \), when it gains an \( \mathrm{H}^+ \), becomes \( \mathrm{CH}_{3} \mathrm{NH}_{3}^{+} \).

Finding the Conjugate Acid for \( \mathrm{OH}^{-} \)

The hydroxide ion, \( \mathrm{OH}^{-} \), turns into water, \( \mathrm{H}_{2} \mathrm{O} \), after it gains an \( \mathrm{H}^+ \).

Finding the Conjugate Acid for \( \mathrm{HCO}_{3}^{-} \)

Bicarbonate ion \( \mathrm{HCO}_{3}^{-} \) becomes \( \mathrm{H}_{2} \mathrm{CO}_{3} \) upon accepting a proton.

Finding the Conjugate Acid for \( \mathrm{H} \)

The atom \( \mathrm{H} \) itself is not typically a base in the Bronsted-Lowry framework; thus, it forms \( \mathrm{H}^{+} \) if forced to gain a proton, but realistically, it’s already a final product.

Key concepts

Conjugate Acid

In the Bronsted-Lowry acid-base theory, every base is paired with a conjugate acid. This transformation occurs when the base gains a proton (H extsuperscript{+}). Once the base accepts the proton, it becomes its conjugate acid.
For example, when sulfate ion (\(\mathrm{SO_3^{2-}}\)) accepts a proton, it becomes the bisulfite ion (\(\mathrm{HSO_3^-}\)). This is a classic case of a conjugate acid being formed.

• The more protons a compound can accept, the stronger the base it is.
• Simply adding an \(\mathrm{H^+}\) to a base gives you its conjugate acid.
• Knowing how to identify conjugate acids helps in understanding chemical reactions.

Conjugate acids are crucial because they determine the direction of an acid-base reaction. Understanding them gives us insight into how molecules will behave in different environments.

Proton Transfer

Proton transfer is the hallmark of acid-base reactions, specifically in the Bronsted-Lowry framework. It occurs when a proton (H extsuperscript{+}) moves from an acid to a base. This mechanism is essential because it defines the transformation between acids and bases.
Let's consider water (\(\mathrm{H_2O}\)) acting as a base. It accepts a proton to form the hydronium ion (\(\mathrm{H_3O^+}\)). Here, the proton from the acid (say, hydrochloric acid) has transferred to the base (water).

• Proton transfer leads to the formation of a conjugate acid from a base.
• Acid-base reactions depend heavily on the pH and strength of the acids and bases involved.
• Understanding proton transfer helps in predicting the direction and outcome of chemical reactions.

This process is not just about rearranging protons; it drives many biochemical and industrial processes that are integral to life and technology.

Acid-Base Reactions

Acid-base reactions are fundamental chemical processes where acids donate protons to bases. The Bronsted-Lowry theory provides a comprehensive framework for understanding these reactions by focusing on proton exchange.
Consider a reaction between ammonia (\(\mathrm{NH_3}\)) and water (\(\mathrm{H_2O}\)). Here, ammonia acts as a base and gains a proton from water, forming ammonium ion (\(\mathrm{NH_4^+}\)) and hydroxide ion (\(\mathrm{OH^-}\)).

• Such reactions are widespread, ranging from neutralizing stomach acid to industrial material synthesis.
• In acid-base reactions, the concept of equilibrium and the risks of reaction reversals are important.
• Salt formation and water production are common results of these reactions.

Mastering acid-base reactions is key to mastering chemistry itself. These reactions showcase how substances interact at a molecular level, influencing countless chemical processes in nature and industry.