Question

Designate the Brønsted-Lowry acid and the BronstedLowry base on the left side of each of the following equations, and also designate the conjugate acid and conjugate base on the right side: (a) \(\mathrm{NH}_{4}{ }^{+}(a q)+\mathrm{CN}^{-}(a q) \rightleftharpoons \mathrm{HCN}(a q)+\mathrm{NH}_{3}(a q)\) (b) \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N}(a q)+\mathrm{H}_{2} \mathrm{O}(I) \rightleftharpoons\) (c) \(\mathrm{HCHO}_{2}(a q)+\mathrm{PO}_{4}{ }^{3-}(a q) \stackrel{\left(\mathrm{CH}_{3}\right)_{3} \mathrm{NH}^{+}(a q)+\mathrm{OH}^{-}(a q)}{\mathrm{CHO}_{2}^{-}(a q)+\mathrm{HPO}_{4}{ }^{2-}(a q)}\)

Short answer

(a) In the equation \(\mathrm{NH}_{4}^{+}(aq)+\mathrm{CN}^{-}(aq) \rightleftharpoons \mathrm{HCN}(aq)+\mathrm{NH}_{3}(aq)\), the Brønsted-Lowry acid is \(\mathrm{NH}_{4}^{+}\), the base is \(\mathrm{CN}^{-}\), the conjugate acid is \(\mathrm{HCN}\), and the conjugate base is \(\mathrm{NH}_{3}\). (b) The complete equation is needed to analyze and identify the acid, base, conjugate acid, and conjugate base. (c) In the equation \(\mathrm{HCHO}_{2}(aq)+\mathrm{PO}_{4}^{3-}(aq) \rightleftharpoons \mathrm{CHO}_{2}^{-}(aq)+\mathrm{HPO}_{4}^{2-}(aq)\), the Brønsted-Lowry acid is \(\mathrm{HCHO}_{2}\), the base is \(\mathrm{PO}_{4}^{3-}\), the conjugate acid is \(\mathrm{HPO}_{4}^{2-}\), and the conjugate base is \(\mathrm{CHO}_{2}^{-}\).

Step-by-step solution

Identify the Brønsted-Lowry acid

The acid is the species that donates a proton (H+ ion). In this case, \(\mathrm{NH}_{4}^{+}\) donates a proton, thus it is the Brønsted-Lowry acid.

Identify the Brønsted-Lowry base

The base is the species that accepts a proton (H+ ion). In this case, \(\mathrm{CN}^{-}\) accepts a proton, thus it is the Brønsted-Lowry base.

Identify the conjugate acid

The conjugate acid is the species obtained after the base accepted a proton. In this case, it is \(\mathrm{HCN}\).

Identify the conjugate base

The conjugate base is the species obtained after the acid donates a proton. In this case, it is \(\mathrm{NH}_{3}\). (b) \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{~N}(a q)+\mathrm{H}_{2}\mathrm{O}(I) \rightleftharpoons\) To analyze this equation, we need the complete equation to identify the acid, base, conjugate acid, and conjugate base. (c) \(\mathrm{HCHO}_{2}(a q)+\mathrm{PO}_{4}{ }^{3-}(a q) \rightleftharpoons \mathrm{CHO}_{2}^{-}(a q)+\mathrm{HPO}_{4}{ }^{2-}(a q)\)

Identify the Brønsted-Lowry acid

The acid is the species that donates a proton (H+ ion). In this case, \(\mathrm{HCHO}_{2}\) donates a proton, thus it is the Brønsted-Lowry acid.

Identify the Brønsted-Lowry base

The base is the species that accepts a proton (H+ ion). In this case, \(\mathrm{PO}_{4}^{3-}\) accepts a proton, thus it is the Brønsted-Lowry base.

Identify the conjugate acid

The conjugate acid is the species obtained after the base accepted a proton. In this case, it is \(\mathrm{HPO}_{4}^{2-}\).

Identify the conjugate base

The conjugate base is the species obtained after the acid donates a proton. In this case, it is \(\mathrm{CHO}_{2}^{-}\).

Key concepts

Conjugate Acid-Base Pairs

In the Brønsted-Lowry Acid-Base Theory, acids and bases exist as pairs known as conjugate acid-base pairs. This concept highlights the reversible nature of acid-base reactions. Here's how it works:- An **acid** donates a proton (H⁺ ion) to become its **conjugate base**.- A **base** accepts a proton to become its **conjugate acid**.In the chemical equation \[\mathrm{NH}_{4}^{+}(aq) + \mathrm{CN}^{-}(aq) \rightleftharpoons \mathrm{HCN}(aq) + \mathrm{NH}_{3}(aq)\],we observe this relationship clearly. - **Before the reaction:** - \(\mathrm{NH}_{4}^{+}\) is the acid, which donates a proton to become \(\mathrm{NH}_{3}\), its conjugate base. - \(\mathrm{CN}^{-}\) is the base, which accepts a proton to become \(\mathrm{HCN}\), its conjugate acid. This pairing is vital for understanding the dynamics of reversible reactions and how acids and bases transform interchangeably.

Proton Transfer

Proton transfer is the fundamental principle behind the Brønsted-Lowry acid-base behavior. This process involves the movement of a proton from an acid to a base, forming their respective conjugate pair. Let's take a look again at \[\mathrm{NH}_{4}^{+}(aq) + \mathrm{CN}^{-}(aq) \rightleftharpoons \mathrm{HCN}(aq) + \mathrm{NH}_{3}(aq)\].- **The journey of the proton:** - The proton is originally with \(\mathrm{NH}_{4}^{+}\). - During the reaction, this proton is transferred to \(\mathrm{CN}^{-}\). - As a result, \(\mathrm{NH}_{3}\) and \(\mathrm{HCN}\) form.This example illustrates a perfect exchange of protons, leading to the formation of new substances. Understanding proton transfer is key for predicting and balancing chemical reactions.

Chemical Equations

Chemical equations are crucial tools in chemistry as they depict the substances involved in a reaction and their transformation. For acid-base reactions, it's about showing which molecules are donating or accepting protons.Take, for instance, the equation:\(\mathrm{HCHO}_{2}(aq) + \mathrm{PO}_{4}^{3-}(aq) \rightleftharpoons \mathrm{CHO}_{2}^{-}(aq) + \mathrm{HPO}_{4}^{2-}(aq)\).- **Equation Analysis:** - **Reactants side:** - \(\mathrm{HCHO}_{2}\) is the acid. - \(\mathrm{PO}_{4}^{3-}\) is the base. - **Products side:** - \(\mathrm{CHO}_{2}^{-}\) is the conjugate base of \(\mathrm{HCHO}_{2}\). - \(\mathrm{HPO}_{4}^{2-}\) is the conjugate acid of \(\mathrm{PO}_{4}^{3-}\).By accurately interpreting these equations, one can determine the role of each component in the reaction, making it easier to predict outcomes of chemical processes.