1 / 13

Acids & Bases

Learn about the properties of acids and bases, and explore the Arrhenius, Brønsted-Lowry, and Lewis acid-base theories. Understand how acids and bases interact and their role in various chemical reactions.

cnedd
Download Presentation

Acids & Bases

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Acids & Bases Chapter 19 Chemistry

  2. Section 1 - Acid-Base Theories Introduction • Bracken Cave, near San Antonio, Texas, is home to twenty to forty million bats. • Visitors to the cave must protect themselves from the dangerous levels of ammonia in the cave. Ammonia is a byproduct of the bats’ urine. • You will learn why ammonia is considered a base.

  3. 1. Properties of Acids and Bases • Acids • Give foods a tart or sour taste • Cause certain chemicals, called indicators, to change color • Can be strong or weak electrolytes in aqueous solution. • A strong electrolyte is a solution in which a large portion of the solute exists as ions • A weak electrolyte isa solution that conducts electricity poorly because only a fraction of the solute exists as ions. • Reacts with many metals to in aqueous solution to produce hydrogen gas. • Reacts with compound containing hydroxide ions to form water and a salt. Citrus fruits contain citric acid. Tea contains tannic acid.

  4. Properties of Acids and Bases (cont.) • Bases • Taste bitter, but tasting most bases is hazardous. • With a few exceptions, none of the foods you eat are bases. • Feels slippery • Ex. Soap • Will change the color of an acid-base indicator • Can be strong or weak electrolytes in aqueous solution. Antacids use bases to neutralize excess stomach acid. The base calcium hydroxide is a component of mortar.

  5. 2. Arrhenius Acids and Bases • Swedish chemist Svante Arrhenius (1859-1927) proposed that acids are hydrogen-containing compounds that ionize to yield hydrogen ions (H+) in aqueous solution. • He also said that bases are compounds that ionize to yield hydroxide ions (OH–) in aqueous solution.

  6. Arrhenius Acids and Bases (cont.) • Arrhenius Acids • Acids that contain one ionizable hydrogen, such as nitric acid (HNO3), are called monoprotic acids. • Acids that contain two ionizable hydrogens, such as sulfuric acid (H2SO4), are called diprotic acids. • Acids that contain three ionizable hydrogens, such as phosphoric acid (H3PO4) are called triprotic acids.

  7. Arrhenius Acids and Bases (cont.) • Not all compounds that contain hydrogen are acids • Not all hydrogens may be released as hydrogen ions. • Only hydrogen ions in very polar bonds are ionizable • In such bonds, hydrogen is joined to a very electronegative element. • When a compound that contains such bonds dissolves in water, it releases hydrogen ions because the hydrogen ions are stabilized by solvation. • Solvation is the process that occurs when an ionic solute dissolves. • Solvent molecules surround the positive and negative ions. Hydrochloric Acid is a polar covalent molecule. It ionizes to form an aqueous solution of hydronium ions and chloride ions.

  8. Arrhenius Acids and Bases • Arrhenius Bases • Bases that contain alkali metals are very soluble in water and dissociate into ions. • Hydroxide ions are one of the products of the dissolution of an alkali metal in water. • Bases that contain alkaline earth metals are not very soluble in water. • Their solutions are always very dilute, even when saturated.

  9. 3. Brønsted-Lowry Acids and Bases • The Arrhenius definition of acids and bases is not a very comprehensive one. • It defines acids and bases rather narrowly and does not include certain substances that have acidic or basic properties. • For example, aqueous solutions of sodium carbonate (Na2CO3 (aq)) and ammonia (NH3 (aq)) are basic. • Neither is a hydroxide, and neither would be classified as a base under the Arrhenius definition. • In 1923, the Danish chemist Johannes Brønsted (1879-1947) and the English chemist Thomas Lowry (1874-1936) proposed that an acid is a hydrogen-ion donor, and a base is a hydrogen-ion acceptor.

  10. Brønsted-Lowry Acids and Bases (cont.) • Conjugate Acids and Bases • Because all gases become less soluble in water as temperature increases, increasing the temperature of an aqueous solution releases gas. • For example, a solution of ammonia gas dissolved in water releases ammonia gas as the temperature increases, which shifts the equilibrium to the left. • A conjugate acid is the particle formed when a base gains a hydrogen ion. • A conjugate baseis the particle that remains when an acid has donated a hydrogen ion.

  11. Brønsted-Lowry Acids and Bases (cont.) • A conjugate acid-base pairconsists of two substances related by the loss or gain of a single hydrogen ion. • A water molecule that gains a hydrogen ion becomes a positively charged hydronium ion (H3O+). • A substance, such as water, that can act as both an acid and a base is said to be amphoteric.

  12. 4. Lewis Acids and Bases • Gilbert Lewis (1875-1946) proposed that an acid accepts a pair of electrons during a reaction, while a base donates a pair of electrons. • This concept is more general than either the Arrhenius or Brønsted-Lowry theory. • A Lewis acidis a substance that can accept a pair of electrons to form a covalent bond. • A Lewis baseis a substance that can donate a pair of electrons to form a covalent bond.

  13. END OF SECTION 1

More Related