8: Acids and Bases
- Page ID
- 142275
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- 8.1: An Introduction to Acids and Bases
- We encounter acids and bases often in our daily lives. For example, heartburn is a buildup of excess stomach acid, which can back up into the esophagus causing a burning sensation. In chemistry, acids and bases have been defined differently by three sets of theories. The simplest theory is the Arrhenius definition, which revolves around the idea that acids are substances that produce hydrogen (H+) ions when in water, whereas bases produce hydroxide (OH-) ions in aqueous solution.
- 8.2: Brønsted-Lowry Acids and Bases
- A compound that can donate a proton (a hydrogen ion) to another compound is called a Brønsted-Lowry acid. The compound that accepts the proton is called a Brønsted-Lowry base. The species remaining after a Brønsted-Lowry acid has lost a proton is the conjugate base of the acid. The species formed when a Brønsted-Lowry base gains a proton is the conjugate acid of the base. Thus, an acid-base reaction occurs when a proton is transferred from an acid to a base.
- 8.3 Lewis Acids and Bases
- Lewis proposed that the electron pair is the dominant actor in acid-base chemistry. An Lewis acid is a substance that accepts a pair of electrons, and in doing so, forms a covalent bond with the entity that supplies the electrons. A Lewis base is a substance that donates an unshared pair of electrons to a recipient species with which the electrons can be shared. Lewis acis/base theory is a powerful tool for describing many chemical reactions used in organic and inorganic chemistry.
- 8.4: Acid Strength and the Acid Dissociation Constant (Ka)
- Acid–base reactions always contain two conjugate acid–base pairs. Each acid and each base has an associated ionization constant that corresponds to its acid or base strength. Two species that differ by only a proton constitute a conjugate acid–base pair. The magnitude of the equilibrium constant for an ionization reaction can be used to determine the relative strengths of acids and bases.
- 8.5: Autoionization of Water and pH
- Water is amphiprotic: it can act as an acid by donating a proton to a base to form the hydroxide ion, or as a base by accepting a proton from an acid to form the hydronium ion ( H3O+ ). The autoionization of liquid water produces OH− and H3O+ ions. The equilibrium constant for this reaction is called the ion-product constant of liquid water (Kw) and is defined as Kw=[H3O+][OH−] . At 25°C, Kw is 1.01×10−14 ; hence pH+pOH=pKw=14.00 .
- 8.6 - Finding the Hydronium Ion Concentration and pH of Strong and Weak Acid Solutions
- If we wish to find the hydronium ion concentration ([H3O+]) and the pH of a solution, we need to know both the strength of the acid (or base) and the concentration of the acid (or base). We will find that we need to treat strong acids (and bases) differently than weak acids (and bases) based on the extent to which they react with water.
- 8.7: The Acid-Base Properties of Ions and Salts
- A salt can dissolve in water to produce a neutral, a basic, or an acidic solution, depending on whether it contains the conjugate base of a weak acid as the anion (A− ), the conjugate acid of a weak base as the cation ( BH+ ), or both. Salts that contain small, highly charged metal ions produce acidic solutions in water. The reaction of a salt with water to produce an acidic or a basic solution is called a hydrolysis reaction.
- 8.8: Buffers: Solutions That Resist pH Change
- Buffers are solutions that resist a change in pH after adding an acid or a base. Buffers contain a weak acid ( HA ) and its conjugate weak base (A−). Adding a strong electrolyte that contains one ion in common with a reaction system that is at equilibrium shifts the equilibrium in such a way as to reduce the concentration of the common ion. Buffers are characterized by their pH range and buffer capacity.
- 8.10: Lewis Acids and Bases
- Lewis proposed that the electron pair is the dominant actor in acid-base chemistry. An Lewis acid is a substance that accepts a pair of electrons, and in doing so, forms a covalent bond with the entity that supplies the electrons. A Lewis base is a substance that donates an unshared pair of electrons to a recipient species with which the electrons can be shared. Lewis acis/base theory is a powerful tool for describing many chemical reactions used in organic and inorganic chemistry.