Question

Write the formula and give the name of the conjugate base of each of the following acids. (a) HCN (b) \(\mathrm{HSO}_{4}^{-}\) (c) HF

Short answer

(a) CN⁻ (cyanide ion), (b) SO₄²⁻ (sulfate ion), (c) F⁻ (fluoride ion).

Step-by-step solution

Understanding Conjugate Base Concept

A conjugate base is what remains after an acid donates a proton \(H^+\). To identify it, simply remove one proton from the acid.

Determining the Conjugate Base of HCN

Start with the acid HCN. When it donates a proton, the hydrogen \(H^+\) is removed. The species left is \(CN^-\), known as the cyanide ion.

Identifying the Conjugate Base of \\mathrm{HSO}_{4}^{-}

For the acid \(\mathrm{HSO}_{4}^{-}\), when the hydrogen is removed, the remaining species is \(\mathrm{SO}_{4}^{2-}\), called the sulfate ion.

Finding the Conjugate Base of HF

Take HF as the acid. When it loses a hydrogen ion, you're left with \(F^-\), which is called the fluoride ion.

Key concepts

Acid-Base Chemistry

Acid-base chemistry is an essential component of chemical reactions and equilibrium. In this context, understanding acids and bases helps us predict how they behave when in contact with each other.
Acids are substances that can donate protons (\( H^+ \)) to other substances. Bases, on the other hand, are substances that can accept these protons or can be identified as the species left after an acid has donated a proton.
In a chemical reaction, when an acid donates its proton, it transforms into its conjugate base. This pair of acid and base, which differ by one proton, illustrate the concept of conjugate acid-base pairs.
Here's a breakdown of the original acids and their corresponding conjugate bases:

• For HCN, the conjugate base is CN^- (cyanide ion).
• For \( \mathrm{HSO}_{4}^{-} \), the conjugate base is \( \mathrm{SO}_{4}^{2-} \) (sulfate ion).
• For HF, the conjugate base is F^- (fluoride ion).

This transformation is pivotal in maintaining the chemical equilibrium and defining the direction of the reaction.

Proton Donation

Proton donation is the hallmark of acidic behavior in a molecule. It refers to the process by which an acid releases a proton (\( H^+ \)) into the surrounding medium, leaving behind its conjugate base.
This is a fundamental process in many chemical reactions, whereby the proton acts as a bridge that facilitates the transfer of charge and the rearrangement of molecules.
Proton donation is what defines an acid's strength; stronger acids donate protons more readily than weaker ones.

• HCN gives away its proton to become CN^-.
• \( \mathrm{HSO}_{4}^{-} \) yields \( \mathrm{SO}_{4}^{2-} \) after proton donation.
• HF transforms into F^- following the donation of a proton.

Identifying which molecule donates the proton helps in determining the roles of substances in a reaction and predicting the outcome of chemical processes.

Ion Identification

Ion identification involves recognizing the ions produced in a reaction, particularly those formed from proton donation. In the realm of acid-base chemistry, identifying the ions is crucial to understanding the behavior of the acid and base components.
In an acid-base reaction, the ion left after a proton is donated is known as the conjugate base. This ion carries the characteristics of the original acid, minus the proton, and carries an additional charge.
To identify ions in an acid-base scenario, follow these cases:

• For HCN, removal of \( H^+ \) results in the identification of CN^- as the ion.
• \( \mathrm{HSO}_{4}^{-} \) transforms to \( \mathrm{SO}_{4}^{2-} \), increasing its negative charge by one.
• HF becomes F^- as the lone remaining ion.

Understanding and identifying these ions help predict how acids and bases react and interact in various environments, crucial for practical applications in chemistry.