Acids and Bases

Acid and Base Overview Acids and bases are a group of compounds that combine to form a salt. A salt is an ionic solid made from a metal and a non-metal Neutralization is the reaction of an acid and a base which forms a salt and water. The resulting salt may or may not be soluble in water. A salt that drops out as a solid in water is called a precipitate

Neutralization Neutralization reaction can be Exothermic=gives off heat Or Endothermic=absorb heat (get cold)

General Characteristics of Acids From Latin word acere meaning “sour” Sour taste Burn to the touch (human skin) Turn litmus (a dye extracted from lichen) red React with metals to release hydrogen gas React with carbonates to release carbon dioxide

General Characteristics of bases Another term for base is “alkali” Alkali and Alkali Earth metals form basic solutions when added to water Bases turn litmus blue Corrosive (eat) organic tissue Do not react with metals or carbonates

Chemical Definition of Acids and Bases Swedish chemist Svante Arrhenius (late 1800s) defined acids/bases on what substances were released in water Acids release hydrogen ions H + Bases release hydroxide ions OH - Explained neutralization reactions but limited to water solutions

Arrhenius Acids and Bases

Lewis Acid/Base Definition Based on electronic configuration Lewis Acid is electron pair acceptor Lewis Base is electron pair donor Useful for gaseous reactions where no water is present

Lewis Acid/Base

Bronsted-Lowry Acid/Base Model Johannes Bronsted and Thomas Lowry Acids are proton donors H + Bases are proton acceptors pH is based off the concentration of H + produced when substance dissociates Dissociate means to break up into ions in solution (usually water)

Bronsted-Lowry The conjugate base is everything that remains of the acid molecule after a proton is lost The conjugate acid is formed when the proton is transferred to the base The relative concentrations of the conjugate acid to conjugate base to the original acid is called the acid dissociation constant or K a Concentrations are figured in molarity

Amphoteric Substances Amphoteric substances can behave like an acid OR a base depending on what they are mixed with Water is amphoteric Liquid ammonia is amphoteric

Dissociation Constants Strong acids produce a high concentration, or dissociate totally, in water. This produces a very high concentration of protons (hydrogen), thus they have a high K a. Strong bases react and take hydrogen ions OUT of solution (proton acceptors), thus bases have very low K a

1. If the H + concentration is M/l, what is the pH? This can be rewritten as 1.0 x M/l since pH = - log [H + ] pH = - (-4) = 4 or place in your calculator and take the log = -4; since pH is - log, = - (-4) = 4

2. If a soil has a pH of 4.7, what is the H + concentration of the soil solution? pH = -log [H + ] 4.7 = -log [H + ] 4.7 = -(- 5) - 0.3; =2.0 (the -5 tells you the number of positions to move the decimal point to the left of =2.0) [H+] = M/l