Acid and Bases: An Introduction

Properties of Acids Sour taste Can produce H+ (hydrogen) ions (protons) Change the color of litmus from blue to red Reacts with metals such as Zn and Mg to produce H2 gas. Ba(s) + H2SO4  BaSO4(aq) + H2(g) Reacts with carbonates (CO32-)to produce CO2 NaHCO3(s) + CH3COOH(aq)  NaCH3COO(aq) + H2O(l) + CO2(g) Acids conduct an electric current

Properties of Bases Bitter or caustic taste A slippery, soapy feeling Can produce OH- (hydroxide) ions Ability to change litmus from red to blue Bases conduct an electric current Bases react with acids to produce a salt and water. This is known as a neutralization reaction. HCl + NaOH  NaCl + H2O HCl + Mg(OH)2  MgCl2 + H2O acid base salt water

Ions in Solution Acidic solutions contains more hydrogen (H+) ions than hydroxide ions (OH-) pH < 7 Basic solutions contains more hydroxide ions (OH-) than hydrogen ions pH > 7 Neutral solutions contain an equal concentration of hydrogen and hydroxide ions pH = 7

Three Definitions of Acids/Bases Type Acid Base Arrhenius H+ producer OH-producer Bronsted-Lowry H+ donor H+ acceptor Lewis Electron-pair acceptor Electron-pair donor

Bronsted-Lowry Conjugate Acid/Base HX(aq) + H2O(l) ⇆ H3O+(aq) + X-(aq) acid base Conjugate Conjugate Acid Base Conjugate acid is the substance produced when a base accepts a hydrogen ion from an acid Conjugate base is the substance that the acid donates a hydrogen ion to form a base

Bronsted-Lowry Conjugate Acid/Base Conjugate acid-base pair consists of two substances related to each other by donating and accepting of a single hydrogen ion NH3(aq) + H2O(l)  NH4+ (aq) + OH-(aq) base acid conjugate conjugate acid base

Practice: Conjugate Acid and Conjugate Base HCO3- + H2S ⇆ H2CO3 + HS- H2PO4- + OH- ⇆ HPO42- + H2O H2SO4 + NH3 ⇆ HSO4- + NH4+ HC2H3O2 + H2O ⇆ H3O+ + C2H3O2-

Question Time Name the three models of acids/bases. What is the Arrhenius model of acids/bases? What is the Bronsted-Lowry Model of Acid bases? What is a conjugate acid and a conjugate base?

Question Time Identify the acid, base, conjugate acid, and conjugate base in the Bronsted-Lowry reactions. NH3 + H2O ⇆ NH4+ + OH- H2O + CH3NH2 ⇆ OH- + CH3NH3+ HF + H2O ⇆ H3O+ + F- HCOOH +CN- ⇆ HCOO- + HCN NH4+ + CO32- ⇆ NH3 + HCO3-

Water in Acid/Base solutions Water and other substances can act as both acids and bases and are said to be amphoteric Hydronium ion = H3O+ = H+ (Remember H+ is a proton) H2O(l) + H2O(l) ⇆ H3O+(aq) + OH-(aq)

Monoprotic and Polyprotic Acids Monoprotic acid donates one hydrogen ion Polyprotic acid donates more than one hydrogen ion

Question Time What is a Lewis acid? What is a Lewis base? What is the H3O+ ion called? What is the shorthand way to write H3O+? What is amphoteric? Give an example.