Question

In each reaction, identify the Bronsted-Lowry acid, the Bronsted-Lowry base, the conjugate acid, and the conjugate base. $$\begin{array}{l}{\text { a. } \operatorname{HI}(a q)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{H}_{3} \mathrm{O}^{+}(a q)+\mathrm{I}(a q)} \\ {\text { b. } \mathrm{CH}_{3} \mathrm{NH}_{2}(a q)+\mathrm{H}_{2} \mathrm{O}(l) \rightleftharpoons \mathrm{CH}_{3} \mathrm{NH}_{3}^{+}(a q)+\mathrm{OH}^{-}(a q)} \\ {\text { c. } \mathrm{CO}_{3}^{2-}(a q)+\mathrm{H}_{2} \mathrm{O}(l) \rightleftharpoons \mathrm{HCO}_{3}^{-}(a q)+\mathrm{OH}^{-}(a q)}\\\ {\text { d. } \mathrm{HBr}(a q)+\mathrm{H}_{2} \mathrm{O}(l) \longrightarrow \mathrm{H}_{3} \mathrm{O}^{+}(a q)+\mathrm{Br}^{-}(a q)}\end{array}$$

Short answer

For each reaction: a. Acid: HI, Base: H2O, Conjugate acid: H3O+, Conjugate base: I-. b. Acid: CH3NH2, Base: H2O, Conjugate acid: CH3NH3+, Conjugate base: OH-. c. Acid: CO32-, Base: H2O, Conjugate acid: HCO3-, Conjugate base: OH-. d. Acid: HBr, Base: H2O, Conjugate acid: H3O+, Conjugate base: Br-.

Step-by-step solution

Identify the Bronsted-Lowry Acid

The Bronsted-Lowry acid is the species that donates a proton (H+) in the reaction. For each reaction, the acid is: a. HI, b. CH3NH2, c. CO32-, d. HBr.

Identify the Bronsted-Lowry Base

The Bronsted-Lowry base is the species that accepts a proton (H+) in the reaction. For each reaction, the base is: a. H2O, b. H2O, c. H2O, d. H2O.

Identify the Conjugate Acid

The conjugate acid is the species formed when a Bronsted-Lowry base gains a proton. For each reaction, the conjugate acid is: a. H3O+, b. CH3NH3+, c. HCO3-, d. H3O+.

Identify the Conjugate Base

The conjugate base is the species formed when a Bronsted-Lowry acid loses a proton. For each reaction, the conjugate base is: a. I-, b. OH-, c. OH-, d. Br-.

Key concepts

Conjugate Acid and Base

Understanding the concept of conjugate acids and bases is fundamental in grasping Bronsted-Lowry acid-base theory. A conjugate acid is created when a base accepts a proton, whereas a conjugate base is formed when an acid donates a proton. In the given reactions, when the Bronsted-Lowry acid, such as HI, releases a proton, it forms its conjugate base, I-. On the flip side, when the Bronsted-Lowry base, like H2O, accepts a proton, it becomes its conjugate acid, which in this case is H3O+.

Remember that conjugate pairs are two species that differ by a single proton. In water's reaction with hydrogen iodide (HI), the water molecule (H2O) acts as a base and accepts a proton, which results in the formation of the hydronium ion (H3O+), now a conjugate acid. The remaining iodide ion (I-) is the conjugate base of HI. Every acid-base reaction includes these two pairs, and identifying them is crucial for perfectly understanding the acid-base processes.

Proton Donor and Acceptor

The Bronsted-Lowry theory categorizes substances based on their ability to donate or accept protons (H+ ions). A proton donor is an acid, while a proton acceptor is a base. For example, in the reaction of methylamine (CH3NH2) with water, CH3NH2 donates a proton and acts as the proton donor or Bronsted-Lowry acid. Water, receiving that proton, is the proton acceptor, making it the Bronsted-Lowry base.

This proton transfer is the heart of an acid-base reaction and can be reversible, leading to what we call equilibrium. The ability to recognize a molecule's potential as a proton donor or acceptor allows chemists to predict and explain the behavior of substances in various chemical reactions, which is a vital skill in chemistry.

Acid-Base Reaction

An acid-base reaction, according to the Bronsted-Lowry theory, involves the transfer of protons from an acid to a base. This reaction is visible in all the examples provided from the textbook exercise. In each one, a proton is moved from the acid to the base, resulting in new substances - the conjugate base and the conjugate acid. Take the reaction between hydrogen bromide (HBr) and water. HBr donates a proton to H2O, leading to the formation of hydronium (H3O+) and bromide ion (Br-).

The shift of a proton from an acid to a base is what characterizes these reactions and determines the pH level of the resulting solution. It's through this understanding that students can start to unravel the complexity of acid-base chemistry and build a foundation for exploring more advanced concepts in chemistry, like buffer solutions and titrations.