Question

Write the formula of the conjugate base of each acid. (a) \(\mathrm{HOCl}\) (b) \(\mathrm{H}_{3} \mathrm{PO}_{4}\) (c) \(\mathrm{HCO}_{3}^{-}\)

Short answer

The conjugate bases are: (a) \( \mathrm{OCl^-} \), (b) \( \mathrm{H}_{2} \mathrm{PO}_{4}^- \), (c) \( \mathrm{CO}_{3}^{2-} \)

Step-by-step solution

Identify acid and remove a proton

For \( \mathrm{HOCl} \), as this is the acid, it will donate a proton. Remove one proton \( \mathrm{H^{+}} \) from it.

Find the conjugate base

After removing one proton from \( \mathrm{HOCl} \), there is \( \mathrm{OCl^-} \) left, which is the conjugate base of \( \mathrm{HOCl} \).

Identify acid and remove a proton

For \( \mathrm{H}_{3} \mathrm{PO}_{4} \), again, as this is the acid, it will donate a proton. So, removing one proton \( \mathrm{H^{+}} \) from it.

Find the conjugate base

After removing one proton from \( \mathrm{H}_{3} \mathrm{PO}_{4} \), there is \( \mathrm{H}_{2} \mathrm{PO}_{4}^- \) left, which is the conjugate base of \( \mathrm{H}_{3} \mathrm{PO}_{4} \).

Identify acid and remove a proton

For \( \mathrm{HCO}_{3}^- \), as this is also an acid, it will donate a proton. So, remove one proton \( \mathrm{H^{+}} \) from it.

Find the conjugate base

After removing one proton from \( \mathrm{HCO}_{3}^- \), there is \( \mathrm{CO}_{3}^{2-} \) left, which is the conjugate base of \( \mathrm{HCO}_{3}^- \).

Key concepts

Acid-Base Chemistry

Understanding acid-base chemistry is essential for comprehending a variety of scientific concepts, especially within the field of chemistry. An acid is a substance that can donate a proton (also known as a hydrogen ion, \(\mathrm{H^{+}}\)) in a chemical reaction, while a base is a substance capable of accepting a proton. The proton transfer from acid to base is a fundamental concept in acid-base reactions.

When an acid loses a proton, it forms what is known as a conjugate base. This conjugate base is now capable of accepting a proton in future reactions, thus displaying the reversibility of acid-base interactions. Similarly, when a base gains a proton, it forms a conjugate acid. This concept of conjugate acid-base pairs is critical, as it allows us to predict the outcomes of acid-base reactions and understand the strength of various acids and bases. In essence, strong acids will have weak conjugate bases because they donate protons easily, whereas weak acids have stronger conjugate bases because they are less willing to lose their proton.

Proton Transfer Reactions

Proton transfer reactions are the heart of acid-base chemistry. They involve the movement of protons between molecules, which typically results in the formation of a new acid and a new base. These reactions are so crucial because they can change the chemical environment of substances and therefore their reactivity.

The ability of a substance to lose or gain protons determines its reactivity in proton transfer reactions. The exercise presented involves such reactions, where an acid (donor of \(\mathrm{H^{+}}\)) is converted into its conjugate base by losing a proton. This process illustrates the Brønsted-Lowry definition of acids and bases, which is particularly useful when dealing with biochemical systems or processes that occur in aqueous solutions. Understanding how to predict the product of a proton transfer is a valuable skill, allowing students to analyze the change in chemical structure and charge of a species after it acts as an acid or a base.

Chemical Formulas

Chemical formulas are the language of chemistry, serving as a concise way to represent the composition of molecules. They tell us the types and quantities of atoms present in a compound, which is critical for understanding its properties and behavior. In the context of acid-base chemistry, chemical formulas become significantly important, as even small changes to a molecular formula can alter the substance's ability to donate or accept protons.

For instance, when examining the chemical formula of an acid, one can identify the potential proton (\(\mathrm{H^{+}}\)) that could be donated and what the resulting conjugate base chemical formula will be post-proton donation. This can be observed through the practice problems provided, where the acid \(\mathrm{HOCl}\) transforms into \(\mathrm{OCl^-}\), \(\mathrm{H}_{3} \mathrm{PO}_{4}\) becomes \(\mathrm{H}_{2} \mathrm{PO}_{4}^-\), and \(\mathrm{HCO}_{3}^-\) turns into \(\mathrm{CO}_{3}^{2-}\) after the removal of \(\mathrm{H^{+}}\). Recognizing and interpreting these chemical formulas helps students predict the behavior of substances during reactions and serves as a stepping stone to mastering more complex concepts in chemistry.