Question

In each reaction, identify the Bronsted-Lowry acid, the BronstedLowry base, the conjugate acid, and the conjugate base. a. \(\mathrm{H}_{2} \mathrm{CO}_{3}(a q)+\mathrm{H}_{2} \mathrm{O}(l) \rightleftharpoons \mathrm{H}_{3} \mathrm{O}^{+}(a q)+\mathrm{HCO}_{3}^{-}(a q)\) b. \(\mathrm{NH}_{3}(a q)+\mathrm{H}_{2} \mathrm{O}(I) \rightleftharpoons \mathrm{NH}_{4}^{+}(a q)+\mathrm{OH}^{-}(a q)\) c. \(\mathrm{HNO}_{3}(a q)+\mathrm{H}_{2} \mathrm{O}(I) \longrightarrow \mathrm{H}_{3} \mathrm{O}^{+}(a q)+\mathrm{NO}_{3}^{-}(a q)\) d. \(\mathrm{C}_{5} \mathrm{H}_{5} \mathrm{~N}(a q)+\mathrm{H}_{2} \mathrm{O}(l) \rightleftharpoons \mathrm{C}_{5} \mathrm{H}_{5} \mathrm{NH}^{+}(a q)+\mathrm{OH}^{-}(a q)\)

Short answer

a. Acid: \(\mathrm{H}_{2}\mathrm{CO}_{3}\), Base: \(\mathrm{H}_{2}\mathrm{O}\), Conjugate Acid: \(\mathrm{H}_{3}\mathrm{O}^{+}\), Conjugate Base: \(\mathrm{HCO}_{3}^{-}\). b. Acid: \(\mathrm{H}_{2}\mathrm{O}\), Base: \(\mathrm{NH}_{3}\), Conjugate Acid: \(\mathrm{NH}_{4}^{+}\), Conjugate Base: \(\mathrm{OH}^{-}\). c. Acid: \(\mathrm{HNO}_{3}\), Base: \(\mathrm{H}_{2}\mathrm{O}\), Conjugate Acid: \(\mathrm{H}_{3}\mathrm{O}^{+}\), Conjugate Base: \(\mathrm{NO}_{3}^{-}\). d. Acid: \(\mathrm{H}_{2}\mathrm{O}\), Base: \(\mathrm{C}_{5}\mathrm{H}_{5}N\), Conjugate Acid: \(\mathrm{C}_{5}\mathrm{H}_{5}NH^{+}\), Conjugate Base: \(\mathrm{OH}^{-}\).

Step-by-step solution

Identify Acids and Bases in Reaction (a)

In reaction (a), the Bronsted-Lowry acid is \(\mathrm{H}_{2}\mathrm{CO}_{3} (aq)\) because it donates a proton (\(H^+\)) to water. Water (\(\mathrm{H}_{2}\mathrm{O}(l)\)) acts as the Bronsted-Lowry base because it accepts the proton, forming \(\mathrm{H}_{3}\mathrm{O}^{+}(aq)\) The conjugate base of the acid is \(\mathrm{HCO}_{3}^{-}(aq)\) and the conjugate acid of the base is \(\mathrm{H}_{3}\mathrm{O}^{+}(aq)\).

Identify Acids and Bases in Reaction (b)

In reaction (b), \(\mathrm{NH}_{3}(aq)\) is the Bronsted-Lowry base because it accepts a proton from water, which acts as the Bronsted-Lowry acid. The products, \(\mathrm{NH}_{4}^{+}(aq)\), is the conjugate acid and \(\mathrm{OH}^{-}(aq)\) is the conjugate base.

Identify Acids and Bases in Reaction (c)

In reaction (c), \(\mathrm{HNO}_{3}(aq)\) is the Bronsted-Lowry acid as it donates a proton to water, which is the Bronsted-Lowry base. This yields \(\mathrm{H}_{3}\mathrm{O}^{+}(aq)\) as the conjugate acid and \(\mathrm{NO}_{3}^{-}(aq)\) as the conjugate base.

Identify Acids and Bases in Reaction (d)

In reaction (d), \(\mathrm{C}_{5}\mathrm{H}_{5}N(aq)\) serves as the Bronsted-Lowry base because it accepts a proton from water. Thus, water is the Bronsted-Lowry acid. The products are \(\mathrm{C}_{5}\mathrm{H}_{5}NH^{+}(aq)\) as the conjugate acid and \(\mathrm{OH}^{-}(aq)\) as the conjugate base.

Key concepts

Conjugate Acid and Base

In the realm of chemistry, understanding the relationship between acids and bases is fundamental. Introduced by Bronsted and Lowry, this concept hinges on the ability of substances to donate or accept protons (hydrogen ions, denoted as \(H^+\)). When an acid surrenders a \(H^+\), it forms a conjugate base, while a base that accepts a \(H^+\) forms a conjugate acid. Let's look closely at reaction (a) as an illustrative example.

In \(\mathrm{H}_{2}\mathrm{CO}_{3}(aq) + \mathrm{H}_{2}\mathrm{O}(l) \rightleftharpoons \mathrm{H}_{3}\mathrm{O}^{+}(aq) + \mathrm{HCO}_{3}^{-}(aq)\), \(\mathrm{H}_{2}\mathrm{CO}_{3}\) donates a \(H^+\) to become \(\mathrm{HCO}_{3}^{-}\), its conjugate base. Similarly, water accepts this \(H^+\) and becomes its conjugate acid, \(\mathrm{H}_{3}\mathrm{O}^{+}\). Thus, a conjugate acid-base pair is formed in this reversible reaction. Conjugate pairs are connected by the reversible loss and gain of a \(H^+\), which is why they play a critical role in understanding chemical equilibria in acid-base reactions.

Real-World Implications

These principles are not just academic; they have practical ramifications in medicine, environmental science, and industrial processes, where the management of pH levels is crucial. Correctly identifying conjugate acids and bases guides chemists in predicting the behavior and direction of reactions.

Acid-Base Reactions

Acid-base reactions are at the heart of chemistry, powering processes from digestion to industrial synthesis. They involve the transfer of \(H^+\) ions between a Bronsted-Lowry acid and base. An acid is a proton donor, and a base is a proton acceptor. Reflecting on the exercises provided, each one showcases an acid-base reaction, evident in the transfer of \(H^+\) from one reactant to another.

For instance, in reaction (b), \(\mathrm{NH}_{3}(aq) + \mathrm{H}_{2}\mathrm{O}(l) \rightleftharpoons \mathrm{NH}_{4}^{+}(aq) + \mathrm{OH}^{-}(aq)\), ammonia grabs a \(H^+\) from water to become ammonium, \(\mathrm{NH}_{4}^{+}\), while water, losing a \(H^+\), becomes hydroxide, \(\mathrm{OH}^{-}\). The acids and bases here swap roles upon reaction, with the reactants' acid becoming the products' base, and vice versa.

Context in Reactions

A spectrum of these reactions exists; some are very fast, while others reach a state of equilibrium. The direction in which a reaction proceeds depends on the relative strengths of the acids and bases involved. This dynamic affects buffering systems in biology, the neutralization processes in titrations, and understanding the environmental impacts of acid rain.

Proton Transfer Reactions

Proton transfer reactions, a subset of acid-base reactions, are ubiquitous in chemical processes. These reactions are predicated on the movement of a single \(H^+\) ion between molecules. When analyzing these transfers, it's vital to identify which substance can lose a proton and which can gain one. Each proton transfer completes an acid-base reaction.

In reaction (c), \(\mathrm{HNO}_{3}(aq) + \mathrm{H}_{2}\mathrm{O}(l) \longrightarrow \mathrm{H}_{3}\mathrm{O}^{+}(aq) + \mathrm{NO}_{3}^{-}(aq)\), nitric acid donates a \(H^+\) to water, hence undergoing a proton transfer and forming a conjugate acid-base pair evident in the final products.

Significance in Chemistry

Understanding proton transfer reactions allows chemists to predict the outcome of reactions, which is essential in fields like pharmaceuticals, where the formulation of drugs must consider proton exchange. Moreover, in biochemistry, proton transfers are central to processes like respiration and energy production in cells. These reactions illustrate that the dance of protons underpins much of the chemical change we observe.