Question

Give the conjugate acid of each of these bases: (a) \(\mathrm{HS}^{-}\) (b) \(\mathrm{HCO}_{3}^{-}\) (c) \(\mathrm{CO}_{3}^{2-}\) (d) \(\mathrm{H}_{2} \mathrm{PO}_{4}^{-}\) (e) \(\mathrm{HPO}_{4}^{2-}, \quad\) (f) \(\mathrm{PO}_{4}^{3-}\) (g) \(\mathrm{HSO}_{4}^{-}\) (h) \(\mathrm{SO}_{4}^{2-}\) (i) \(\mathrm{NO}_{2}^{-}\) (j) \(\mathrm{SO}_{3}^{2-}\)

Short answer

The conjugate acids are: (a) \(H_{2}S\), (b) \(H_{2}CO_{3}\), (c) \(HCO_{3}^{-}\), (d) \(H_{3}PO_{4}\), (e) \(H_{2}PO_{4}^{-}\), (f) \(HPO_{4}^{2-}\), (g) \(H_{2}SO_{4}\), (h) \(HSO_{4}^{-}\), (i) \(HNO_{2}\), and (j) \(HSO_{3}^{-}\).

Step-by-step solution

Identifying the conjugate acid of \(HS^{-}\)

Adding a proton (\(H^{+}\)) to \(HS^{-}\) forms the conjugate acid \(H_{2}S\), as the negative charge is neutralized by the proton.

Identifying the conjugate acid of \(HCO_{3}^{-}\)

Adding a proton to \(HCO_{3}^{-}\) leads to \(H_{2}CO_{3}\), which is the matching conjugate acid.

Identifying the conjugate acid of \(CO_{3}^{2-}\)

In this case, adding a proton to \(CO_{3}^{2-}\) results in \(HCO_{3}^{-}\), balancing, and reducing the negative charge by one.

Identifying the conjugate acid of \(H_{2}PO_{4}^{-}\)

Add a proton to \(H_{2}PO_{4}^{-}\) to form \(H_{3}PO_{4}\), thereby neutralizing the negative charge and forming the conjugate acid.

Identifying the conjugate acid of \(HPO_{4}^{2-}\)

Adding a proton to \(HPO_{4}^{2-}\) forms \(H_{2}PO_{4}^{-}\), reducing the negative charge by one.

Identifying the conjugate acid of \(PO_{4}^{3-}\)

Adding a proton to \(PO_{4}^{3-}\) forms \(HPO_{4}^{2-}\), reducing the charge by one.

Identifying the conjugate acid of \(HSO_{4}^{-}\)

By adding a proton to \(HSO_{4}^{-}\), \(H_{2}SO_{4}\) is formed, neutralizing the negative charge.

Identifying the conjugate acid of \(SO_{4}^{2-}\)

Adding a proton to \(SO_{4}^{2-}\) results in \(HSO_{4}^{-}\), reducing the negative charge by one.

Identifying the conjugate acid of \(NO_{2}^{-}\)

Adding a proton to \(NO_{2}^{-}\) results in \(HNO_{2}\), neutralizing the negative charge.

Identifying the conjugate acid of \(SO_{3}^{2-}\)

If a proton is added to \(SO_{3}^{2-}\), \(HSO_{3}^{-}\) is created, reducing the charge by one.

Key concepts

Acid-Base Reactions

Acid-base reactions are fundamental in chemistry, involving the transfer of protons (H⁺ ions) between substances. This concept is essential to understand how conjugate acids and bases work.
When a base accepts a proton, it forms its conjugate acid, effectively becoming the counterpart in the chemical exchange.

• Acids are proton donors.
• Bases are proton acceptors.
• The reaction results in the formation of a conjugate acid and a conjugate base.

Recognizing conjugate pairs is crucial. For instance, when \\(\mathrm{HS}^{-}\) accepts a proton, it becomes \\(\mathrm{H_{2}S}\), its conjugate acid. Each addition of a proton to a base decreases its negative charge, making it more positive, shifting the balance of the reaction.

Proton Transfer

Proton transfer is the process at the heart of acid-base reactions. Whenever a base gains a proton (H⁺), the charge of the molecule changes, often leading to a new compound. It's a simple transformation but pivotal in many chemical processes.
Understanding this helps you determine the conjugate acid of a given base.

• A negative ion will become neutral or less negative when it gains a proton.
• This transfer is what changes \(\mathrm{CO_{3}^{2-}}\) to \(\mathrm{HCO_{3}^{-}}\).
• The charge reduction is by exactly one because a single proton is transferred.

Atomically, adding an H⁺ means rearranging bonds and sometimes creating a new structure. It's these little changes that are the foundation of huge chemical reactions.

Negative Charge Neutralization

Negative charge neutralization happens when a molecule's charge becomes less negative through proton addition. This balancing act is key in turning a base into its conjugate acid. By neutralizing the charge, stability is often increased.
When you add a proton:

• The molecule's charge will drop by one negative unit.
• Neutralization makes a new compound, such as how \(\mathrm{PO_{4}^{3-}}\) becomes \(\mathrm{HPO_{4}^{2-}}\).
• It’s an important concept for achieving balance in solution chemistry.

This charge adjustment is what chemists use to predict reactions and understand molecule behaviors. Learning how negative charges are neutralized provides insight into how acids and bases adjust their forms in different environments.