Question

Match the key terms with the descriptions provided. (a) an acid that ionizes completely when dissolved in water (b) a model that describes acids as substances that generate \(\mathrm{H}^{+}\)ions in solution and bases as substances that generate \(\mathrm{OH}^{-}\)ions in solution (c) an aqueous hydrogen ion; \(\mathrm{H}_{3} \mathrm{O}^{+}(\mathrm{aq})\) (d) a solution in which the \(\mathrm{OH}^{-}\)concentration is greater than the \(\mathrm{H}_{3} \mathrm{O}^{*}\) concentration; a solution with a \(\mathrm{pH}\) greater than 7 (e) an acid that does not completely ionize when dissolved in water (f) a substance that forms after an acid loses an \(\mathrm{H}^{+}\)ion (g) an equilibrium constant for the ionization of an acid in water; a value that expresses the strength of a weak acid (h) a measure of the acidity of aqueous solutions; the negative logarithm of the \(\mathrm{H}_{3} \mathrm{O}^{*}\) concentration (i) a combination of a weak acid and its conjugate base (or a weak base and its conjugate acid) in similar amounts; when in solution, something that helps prevent large changes in \(\mathrm{pH}\) when small amounts of \(\mathrm{H}_{3} \mathrm{O}^{+}(a q)\) or \(\mathrm{OH}^{-}(a q)\) are added

Short answer

The accurate matches of key terms with their respective definitions are: (a) Strong Acid, (b) Arrhenius Model, (c) Hydronium Ion, (d) Basic or Alkaline Solution, (e) Weak Acid, (f) Conjugate Base, (g) Acid Dissociation Constant (Ka), (h) pH, (i) Buffering System.

Step-by-step solution

Identify Terms and Definitions

The first step is to use prior knowledge or reference materials to identify the definitions of the following terms: strong acid, Arrhenius model, hydronium ion, basic or alkaline solution, weak acid, conjugate base, acid dissociation constant (Ka), pH, and buffering system.

Match Key Terms with Descriptions

Matching each term with their correct definition yields the following: \n (a) a strong acid \n(b) Arrhenius model \n(c) hydronium ion \n(d) basic or alkaline solution \n(e) weak acid \n(f) conjugate base \n(g) acid dissociation constant (Ka) \n(h) pH \n(i) buffering system.

Confirm Matches

Double-check each match to ensure its accuracy. It is recommended to understand not just the definitions but the relevance and application of each term in the context of acid-base chemistry. This provides a deeper understanding and application of these terms.

Key concepts

Strong Acid

When discussing strong acids, these are substances that completely ionize in water, releasing all their hydrogen ions (H⁺) into solution. This means that when a strong acid dissolves, it produces a high concentration of hydronium ions (H₃O⁺). This is significant because the complete ionization leads to highly acidic solutions with low pH values. Common examples include hydrochloric acid (HCl) and sulfuric acid (H₂SO₄).

In acid-base reactions, strong acids readily donate H⁺ ions, making them highly reactive. Because they completely dissociate, the reaction direction favors the formation of products (the ions), and there is virtually no reverse reaction to reform the acid. This concept is crucial when predicting reaction outcomes and understanding the pH changes in solutions.

Arrhenius Model

The Arrhenius model is a foundational concept in acid-base chemistry. It defines acids as substances that increase the concentration of hydrogen ions (H⁺) when dissolved in water, and bases as substances that increase the concentration of hydroxide ions (OH^-). This model is particularly helpful for beginners as it provides a clear and simple way to identify acids and bases in aqueous solutions.

This model, however, has its limitations. It doesn't account for substances that can act as acids or bases without producing hydrogen or hydroxide ions. Later models, such as the Brønsted-Lowry and Lewis theories, expand on the Arrhenius model by explaining acid-base reactions that don't involve water or result in the formation of ions not covered by Arrhenius's definitions.

Hydronium Ion

The hydronium ion is denoted as H₃O⁺ and plays a pivotal role in the Arrhenius model of acid-base chemistry. It forms when a hydrogen ion (H⁺), which is simply a proton due to the absence of electrons, associates with a water molecule (H₂O). This bonding is frequent because hydrogen ions are too reactive to exist freely in solution. The concentration of hydronium ions in a solution determines its acidity.

Understanding the formation and role of hydronium ions is essential when calculating pH values and understanding how acids behave in water. The more hydronium ions present, the more acidic the solution, hence a lower pH.

Basic Solution

A basic solution, sometimes referred to as alkaline, is characterized by having a higher concentration of hydroxide ions (OH^-) than hydronium ions (H₃O⁺). In basic solutions, the pH value is greater than 7, indicating a lower concentration of H₃O⁺ and therefore less acidity.

Household items like baking soda and soap often create basic solutions when dissolved in water. These solutions can neutralize acids, which is a fundamental aspect of titration—a method used to determine an unknown concentration of an acid using a known concentration of a base.

Weak Acid

In contrast to strong acids, a weak acid does not fully ionize in solution. This means that only a fraction of the acid molecules release hydrogen ions (H⁺), resulting in an equilibrium state where both the acid and its ions coexist in solution. Acetic acid (CH₃COOH), commonly found in vinegar, is a typical example.

The incomplete ionization of weak acids is crucial to understand because it affects the pH of the solution and the workings of buffer systems. Weak acids are often involved in complex reactions where both the forward (ionization) and reverse (recombination) reactions occur simultaneously. This dynamic is described quantitatively by the acid's dissociation constant.

Conjugate Base

When an acid loses a hydrogen ion (H⁺), it forms a conjugate base. This concept is part of the Brønsted-Lowry theory, which complements the Arrhenius model by considering proton transfer. The conjugate base is what remains of the acid molecule after it donates a proton. For instance, when the weak acid acetic acid loses a proton, it forms the acetate ion (CH₃COO^-).

Seeing acids and bases as conjugate pairs helps us predict the direction of the reaction and understand the strength of acids and bases. A strong acid has a weak conjugate base, while a weak acid has a relatively stronger conjugate base. This relationship is essential for predicting the outcomes of chemical reactions and designing buffer systems.

Acid Dissociation Constant

The acid dissociation constant (K_a) is a value that measures the strength of weak acids. It is the equilibrium constant for the ionization of an acid in water. Essentially, it tells us to what extent an acid donates protons when dissolved in water. The larger the K_a, the stronger the acid because it means a greater portion of the acid molecules ionize to form hydrogen ions.

Calculating this constant involves measuring the concentration of the reactants (weak acid) and products (conjugate base and H⁺) in a solution at equilibrium. This understanding aids in predicting the behavior of acids in various chemical environments, especially in biological processes where slight changes in acid strength can have significant implications.

pH

The power of hydrogen, or pH, is a scale used to specify the acidity or basicity of an aqueous solution. It is the negative logarithm of the hydronium ion concentration (log[H₃O⁺]). The pH scale ranges from 0 to 14, with 7 being neutral. Values less than 7 indicate acidity, while values greater than 7 indicate basicity.

The pH scale is logarithmic, which means each whole pH value represents a tenfold change in hydrogen ion concentration. For instance, a solution with a pH of 3 is ten times more acidic than one with a pH of 4. This concept is vital in all sciences, particularly in chemistry and biology, where the pH can influence chemical reactions and biological processes.

Buffering System

A buffering system consists of a mixture of a weak acid and its conjugate base (or a weak base and its conjugate acid). Buffers are used to maintain a stable pH in a solution, even when small quantities of an acid or base are added. They work by absorbing excess hydrogen ions (H⁺) or hydroxide ions (OH^-) to minimize the change in pH. This property is crucial in biological systems, such as blood, where maintaining a precise pH is vital for proper function.

Buffers are critical in many industrial and laboratory processes and are important in everyday products like medications and personal care items. Understanding how they function helps us control chemical reactions, preserve the stability of substances, and comprehend natural physiological processes.