Problem 1 - Chemistry and Chemical Reactivity

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

Step-by-Step Solution

Answer

(a) CN⁻ (cyanide ion), (b) \(\mathrm{SO}_{4}^{2-}\) (sulfate ion), (c) F⁻ (fluoride ion)

Step 1: Understanding Conjugate Acids and Bases

The conjugate base of an acid is formed when the acid donates a proton (H⁺). Therefore, to find the conjugate base, we simply remove one H⁺ from the acid and decrease its charge by one.

Step 1: Finding the Conjugate Base of HCN

To find the conjugate base of HCN, remove one H⁺ ion from HCN. Removing one hydrogen atom from HCN leaves behind the cyanide ion, CN⁻. Thus, the conjugate base of HCN is CN⁻.

Step 2: Finding the Conjugate Base of \(\mathrm{HSO}_{4}^{-}\)

For \(\mathrm{HSO}_{4}^{-}\), remove one H⁺ ion. Removing one proton from \(\mathrm{HSO}_{4}^{-}\) results in the formation of the sulfate ion, \(\mathrm{SO}_{4}^{2-}\). Thus, the conjugate base of \(\mathrm{HSO}_{4}^{-}\) is \(\mathrm{SO}_{4}^{2-}\).

Step 3: Finding the Conjugate Base of HF

To find the conjugate base of HF, remove one H⁺ ion. This results in the fluoride ion, F⁻. Therefore, the conjugate base of HF is F⁻.

Key Concepts

Proton Removal

In chemistry, understanding proton removal is key to identifying conjugate bases. When an acid loses a hydrogen ion (H⁺), it forms its conjugate base. This process involves the removal of a proton, which is a defining step in acid-base reactions. The removal of a proton:

• Decreases the charge of the molecule by one.
• Transforms the acid into its conjugate base.

For example, in the reaction where hydrofluoric acid (HF) loses a proton, it becomes the fluoride ion (F⁻). This simple proton transfer is a fundamental concept in understanding how acids and bases interact.

Cyanide Ion

The cyanide ion (CN⁻) is the conjugate base of hydrogen cyanide (HCN). When HCN loses a proton, it transforms into CN⁻. The cyanide ion:

• Has a negative charge, indicating the loss of one proton from its parent acid.
• Is a simple ion composed of one carbon and one nitrogen atom.

Cyanide is known for being a strong nucleophile and for its biological reactivity. In this context, it is an example of how removing a proton from an acid results in a conjugate base that can participate in further reactions.

Sulfate Ion

When considering the sulfate ion (\(\mathrm{SO}_{4}^{2-}\)), it serves as the conjugate base of hydrogen sulfate (\(\mathrm{HSO}_{4}^{-}\)). By removing one proton from \(\mathrm{HSO}_{4}^{-}\), the charge is reduced and the sulfate ion forms. The sulfate ion:

• Has a double negative charge, reflecting the loss of a proton from its hydrogen sulfate form.
• Is comprised of one sulfur atom bonded to four oxygen atoms.

The ion is significant in many chemical and biological systems, illustrating the result of proton removal in acid-base chemistry.

Fluoride Ion

The fluoride ion (F⁻) is what we get when hydrofluoric acid (HF) loses a proton. This conversion is straightforward:

• It involves only one hydrogen being removed to form the fluoride ion.
• The resulting ion carries a negative charge.

Fluoride ions are well-known for their roles in dental health and various industrial applications. This process exemplifies an essential principle of acid-base reactions, where the removal of a proton transforms an acid into its conjugate base.