Introduction to Acids & Bases Packet #19

Introduction Acids are group of ionic compounds with unique properties and are found everywhere Cause lemons to be sour Allows for digestion of food in the stomach Dissolve one’s tooth enamel to cause cavities Eighty billion pounds of sulfuric acid, H 2 SO 4, is used every year in the United States to help manufacture Detergents Batteries Plastics Pharmaceuticals Storage batteries Metals

Introduction II Acids were first recognized as substances that taste sour. While bases, sometimes called alkalis, are characterized by their bitter taste and slippery feel.

Introduction III Svante Arrhenius was the first person to recognize the essential nature of acids and bases.

Introduction IV Arrhenius postulated that: Acids produce hydrogen ions (H + ) in an aqueous solution Bases produce hydroxide ions (OH - ) in an aqueous solution. The limitation of Arrhenius’ concept was that OH - was the only base that could be produced. HCl(g)  H + (aq) + Cl - (aq) NaOH(s)  Na + (aq) + OH - (aq) Top reaction The product produced is hydrochloric acid. Both products are in the aqueous form Bottom reaction The bottom reaction occurs when sodium hydroxide, is placed in water. Produces a strong base as the solution. H2OH2O H2OH2O

Introduction V Bronsted-Lowry In the Bronsted-Lowry model: - An acid is a proton (H+) donor A base is a proton (H+) acceptor This results in the formation of a new acid, called the conjugate acid, and a new base called the conjugate base.

Introduction VI Bronsted-Lowry Acids & Bases HA(aq) + H 2 O(l)  H 3 O + (aq) + A - (aq) Acid + Base  Conjugate acid + Conjugate Base Example HCl(aq) + H 2 O(l)  H 3 O + (aq) + Cl - (aq) HCl(aq) and Cl - become the acid-conjugate base pair H 2 O(aq) and H 3 O + (aq) become the base-acid conjugate base pair. A conjugate acid-base pair consists of two substances relate to each other by the donating and accepting of a single proton.

Examples Which of the following represent conjugate acid-base pairs? a.HF, F - b.NH 4 +, NH 3 c.HCl, H 2 O d.A & B are correct e.B & C are correct f.A & C are correct g.All of the above are correct h.None of the above is correct

Introduction VII A third theory of acids and bases was propose by Gilbert Lewis (1875 – 1946) Lewis proposed that an acid accepts a pair of electrons during a chemical reaction while a base donates a pair of electrons. Much more general than Arrhenius theory or the Bronsted-Lowry theory.

Introduction VIII Lewis Acids & Bases

NAMING ACIDS

Naming Acids I AcidsAcids Compounds that are proton (H + ) donors.Compounds that are proton (H + ) donors. Formulas usually begin with ‘H’.Formulas usually begin with ‘H’. The general formula for acids is H n XThe general formula for acids is H n X X represents the anionX represents the anion Examples:Examples: HCl (aq) – hydrochloric acidHCl (aq) – hydrochloric acid HNO 3 – nitric acidHNO 3 – nitric acid H 2 SO 4 – sulfuric acidH 2 SO 4 – sulfuric acid

Naming Acids II Remember The general formula for acids is H n XThe general formula for acids is H n X Follow these three rules when attempting to name acids

Rule #1 {Monoatomic anions} Remember H n X When the name of the anion (X) ends with –ide The acid begins with the prefix hydro- AND the stem of the anion has the suffix –ic. The word acid follows. Example X = Cl - = chloride Therefore the acid’s molecular formula is HCl Remember from previous lecture on ions The name of the acid becomes hydrochloric acid.

Rule #2 {Polyatomic ions} Remember H n X When the anion name ends in –ite. The acid name is the stem of the anion with the suffix –ous. The word acid follows. Example Name the acid H 2 SO 3 What is the name of the polyatomic anion? Sulfite What is the name of the acid? Sulfurous acid

Rule #3 {Polyatomic anions} Remember H n X When the anion ends in the name –ate The acid name is the stem of the anion with the suffix –ic. The word acid follows. Example HNO 3 What is the polyatomic ion? X = NO 3 = nitrate Therefore the acid’s name is nitric acid.

NAMING BASES

Naming Bases I Bases are named in the same way as other ionic compounds. The name of the cation followed by the name of the anion. Example NaOH Sodium hydroxide Al(OH) 3 Aluminum hydroxide

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