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Unit VII Chapter 15 Properties • Both acids and bases ionize or dissociate in water • Acids: taste sour, conduct electricity, cause certain indicators to change color, and react with metals to form H2 gas • Bases: taste bitter, feel slippery, conduct electricity, and cause certain indicators to change color Recognizing Acids and Bases • Most simply, acids tend to have H’s at the beginning of their chemical formulas. • Bases tend to have OH’s at the end of their formulas. • NOTE: THIS IS NOT THE WHOLE TRUTH...YOU’LL LEARN MORE SOON! Naming Acids and Bases • REVIEW: • Binary acids • Oxyacids • Bases (named simply as ionic compounds) • pg. 454-458 Acid Nomenclature Review Anion Ending Binary Acid Name -ide hydro-(stem)-ic acid -ate (stem)-ic acid -ite (stem)-ous acid oxyacid An easy way to remember which goes with which… “In the cafeteria, you ATE something ICky” Practice Problems Answers: 1. 2. 3. 4. HF HNO3 KOH H2SO4 1. Hydrofluoric acid 2. Nitric acid 3. Potassium hydroxide 4. Sulfuric acid Practice Problem Answers: 1. 2. 3. 4. Chromic acid Iron (II) hydroxide Acetic Acid Lithium hydroxide 1. H2CrO4 2. Fe(OH)2 3. CH3COOH 4. LiOH Acid/Base Strength • The Strength of an acid/base depends on the degree of ionization/dissociation. • Common Aqueous Acids and Bases: Tables 15-3 and 15-4 Acid/Base Definitions • Arrhenius Acids/Bases • Earliest and most specific definition • Brønted-Lowry Acids/Bases • Middle definition • Lewis Acids/Bases • Latest and most general definition Arrhenius Acid Definition • An acid is a compound that increases hydrogen ions [H+] concentration when dissolved in water. • Ex. HCl(g) is named hydrogen chloride. BUT HCl(aq) is named hydrochloric acid. Arrhenius Base Definition • A base is a compound that increases hydroxide ion [OH-] concentration when dissolved in water. • Ex. NaOH(s) is named sodium hydroxide and is NOT a base. BUT NaOH (aq) is named sodium hydroxide and IS a base. Acidic Solutions • An acidic solution is one in which [H3O+] is greater than [OH-]. • Ex. • HCl(g) H 2O H+ (aq) + Cl- (aq) • Since the water is already forming some H+ ions (typically in the form of H3O+), the HCl is adding more H+ ions. This causes there to be MORE H+ or H3O+ ions than OH- ions. Basic Solutions • A basic solution is one in which [OH-] is greater than [H3O+]. • AKA: alkaline solutions • Ex. • NaOH(s) H2O Na+(aq) + OH-(aq) • Since the water is already forming some OHions, NaOH is adding more OH- ions. This causes there to be MORE OH- ions than H3O+ ions. Arrhenius Acids and Bases • Acids are hydrogen-containing compounds that ionize to yield hydrogen ions in aqueous solution... • Bases are compounds that ionize to yield hydroxide ions in aqueous solution... • BUT...NH3 is a base! Arrhenius’ theory doesn’t hold up in every case, so... Brønsted-Lowry Acids and Bases • An acid is a hydrogen-ion donor, and a base is a hydrogen-ion acceptor. • A substance that can either accept or donate depending upon its partner is call amphoteric. • Example: NH3(aq) + H2O(l) NH4+(aq) + OH-(aq) • Watch the compounds as they react. What happens across the arrow? Practice Problem • H2SO4 + H2O H3O+ + HSO4- • Label the acid, base, conjugate acid, and conjugate base. Lewis Acid/Base Definition Lewis acid - a substance that accepts an electron pair Lewis base - a substance that donates an electron pair Lewis Acids & Bases Formation of hydronium ion is also an excellent example. H + ACID •• •• O—H H BASE •• H O—H H •Electron pair of the new O-H bond originates on the Lewis base. Lewis Acid/Base Reaction Conjugate Acids and Bases • Every acid on the left side of the reaction equation has a conjugate base on the right side of the equation. • There is also the same base/conjugate acid pairing in each equation. Conjugate pairs Practice problems Identify the acid, base, conjugate acid, conjugate base, and conjugate acid-base pairs: HC2H3O2(aq) + H2O(l) C2H3O2–(aq) + H3O+(aq) acid base conjugate base conjugate acid conjugate acid-base pairs OH –(aq) + HCO3–(aq) CO32–(aq) + H2O(l) base acid conjugate base conjugate acid conjugate acid-base pairs Strength of conjugates • The stronger the acid/base, the weaker the conjugate base/acid is. • See Table 15-6 p.471 • Ex: HCl(acid)-Strong acid Cl-(conj. base)-very weak base Neutral Solutions • Any aqueous solution in which [OH-] = [H3O+] is described as a neutral solution. • Ex. Pure water • Neutralization Reactions are based on equalizing the conc. of acids and bases in solution. (Titration)