Problem 2 - Chemistry and Chemical Reactivity

Question

Write the formula and give the name of the conjugate acid of each of the following bases. (a) \(\mathrm{NH}_{3}\) (b) \(\mathrm{HCO}_{3}^{-}\) (c) \(\mathrm{Br}^{-}\)

Step-by-Step Solution

Answer

(a) \(\mathrm{NH}_4^{+}\), (b) \(\mathrm{H_2CO_3}\), (c) \(\mathrm{HBr}\)

Step 1: Understanding Conjugate Acid

A conjugate acid is formed when a base gains a proton (\(\text{H}^{+}\)). To find the conjugate acid of a base, simply add an \(\text{H}^{+}\) to it.

Step 1: Conjugate Acid of \(\mathrm{NH}_3\)

The base is \(\mathrm{NH}_3\). Add an \(\text{H}^{+}\) ion: \[\mathrm{NH}_3 + \text{H}^{+} \rightarrow \mathrm{NH}_4^{+}\] The conjugate acid of \(\mathrm{NH}_3\) is \(\mathrm{NH}_4^{+}\) (ammonium ion).

Step 2: Conjugate Acid of \(\mathrm{HCO}_3^{-}\)

The base is \(\mathrm{HCO}_3^{-}\). Add an \(\text{H}^{+}\) ion: \[\mathrm{HCO}_3^{-} + \text{H}^{+} \rightarrow \mathrm{H_2CO_3}\] The conjugate acid of \(\mathrm{HCO}_3^{-}\) is \(\mathrm{H_2CO_3}\) (carbonic acid).

Step 3: Conjugate Acid of \(\mathrm{Br}^{-}\)

The base is \(\mathrm{Br}^{-}\). Add an \(\text{H}^{+}\) ion: \[\mathrm{Br}^{-} + \text{H}^{+} \rightarrow \mathrm{HBr}\] The conjugate acid of \(\mathrm{Br}^{-}\) is \(\mathrm{HBr}\) (hydrobromic acid).

Key Concepts

Protonation

Protonation is a key concept in understanding how conjugate acids form. It refers to the process where a proton (\(\text{H}^+\)) is added to a molecule or an ion. In acid-base chemistry, protonation changes a base into its conjugate acid. When a base receives a proton, it increases in positive charge because the proton itself carries a positive charge. This process is essential in many chemical reactions, as it helps in stabilizing molecules and allows them to participate in further reactions.
Examples of protonation:

• When ammonia (\(\text{NH}_3\)) gains a proton, it turns into ammonium ion (\(\text{NH}_4^+\)).
• A bicarbonate ion (\(\text{HCO}_3^-\)) gaining a proton becomes carbonic acid (\(\text{H}_2\text{CO}_3\)).
• The bromide ion (\(\text{Br}^-\)) becomes hydrobromic acid (\(\text{HBr}\)) after protonation.

Acid-Base Chemistry

Acid-base chemistry deals with the reactions and processes involving acids and bases. It is essential for understanding the formation of conjugate acids and bases. According to the Brønsted-Lowry definition, an acid is a proton donor, and a base is a proton acceptor.
When a base accepts a proton, it forms its conjugate acid, completing the acid-base pair. This pair is linked by their ability to transform into one another by the gain or loss of a proton. Acid-base reactions often involve switching protons between molecules, helping to balance chemical equations and maintain equilibrium in solutions.
Key points in acid-base chemistry:

• Every acid has a conjugate base, and every base has a conjugate acid.
• The strength of an acid or base is determined by how easily it gives up or accepts a proton.
• Acid-base reactions are fundamental in buffering solutions, digestion, and other biological processes.

Chemical Formulas

Chemical formulas are critical for representing substances in chemistry. They provide information about the types and numbers of atoms present in a substance. For example, the chemical formula \(\text{NH}_3\) tells us that ammonia consists of one nitrogen atom and three hydrogen atoms.
Chemical formulas also help us understand the changes that occur during chemical reactions. For example, in protonation, ammonia (\(\text{NH}_3\)) becomes ammonium (\(\text{NH}_4^+\)) as a proton is added. This results in a change in the number of hydrogen atoms and the overall charge of the compound.
Considerations when using chemical formulas:

• They must always reflect the correct stoichiometry—the balanced numbers of each type of atom.
• They show the balance of charges, especially in ionic compounds, like when neutral \(\text{NH}_3\) becomes positively charged \(\text{NH}_4^+\).
• Understanding formulas enables predicting the outcomes of chemical reactions and interactions.