Acid-Base Reactions Section 14.3

Conjugate Base Conjugate base: the species that remains after a Brønsted-Lowry acid has given up a proton Acid conjugate base

Conjugate Acid Conjugate acid: the species that is formed when a Brønsted-Lowry base gains a proton base conjugate acid

Acid-Base Reactions Usually acid-base reactions are equilibrium systems The forward and reverse reactions occur They involve conjugate acid-base pairs CH3COOH(aq) + H2O(l) H3O+(aq) + CH3COO - (aq)acid base conjugate conjugate acid base Do activity with acid base reactions here: write various reactions on the board and have students label them with cards that have acid, base, conjugate acid and conjugate base on them

Strength of Conjugate Acids and Bases The stronger an acid is, the weaker its conjugate base The stronger a base is, the weaker its conjugate acid

Amphoteric Compounds Amphoteric: any species that can react as either an acid or a base Example: H2O can act as either an acid or a base H2SO4(aq) + H2O(l) H3O+(aq) + HSO4-(aq) NH3(g) + H2O(l) NH+4(aq) + OH-(aq)

Continued The amphoteric substance acts as either an acid or a base depending on the strength of the acid or base with which it is reacting

Neutralization Reactions A strong acid and a strong base react to form a salt and water Aqueous HCl completely dissociates in water to form H3O+ and Cl- Aqueous NaOH completely dissociates in water to form Na+ and OH-

Strong Acid + Strong Base NaOH(aq) + HCl(aq)  NaCl(aq) and H2O(l)

Vocabulary Neutralization: (in aqueous solutions) the reaction of hydronium ions and hydroxide ions to form water molecules Salt: an ionic compound composed of a cation from a base and an anion from an acid

Acid Rain Pure rain water is slightly acidic because of dissolved carbon dioxide that forms carbonic acid with a pH = 5.6 Acid rain is defined as rain with a pH < 5.6 Other acids cause rain to have a lower pH

More about Acid Rain Main “evil” acids in rain are sulfuric acid and nitric acid Caused by the reaction of oxides of sulfur and oxides of nitrogen Can be deposited in rain water, fog, or snow Drastically affects lakes, streams, ponds and soil