Created by C. Ippolito

January 2007

Acids, Bases, and Salts

Objectives:1.1. DistinguishDistinguish among strong, weak, and non electrolytes2.2. CompareCompare Arrhenius and Brønsted-Lowry theories3.3. DeriveDerive ionization constants of acids4.4. DescribeDescribe properties of acids, bases, and salts5.5. ExplainExplain conjugate acid-base pairs and amphoteric

substances

Created by C. Ippolito

January 2007

Theory of Ionization

• ElectrolytesElectrolytes– substances that conduct electricity when in aqueous

solutions

• NonelectrolytesNonelectrolytes– substances that do not conduct electricity when in

aqueous solutions

• Arrhenius’ Theory of IonizationArrhenius’ Theory of Ionization– electrolytes breakdown into small particles (ion)

– the particles conduct current

Created by C. Ippolito

January 2007

Ionic Electrolytes

• Disassociation– dissolved ionic solids separate into cations and

anions– each ion is hydratedhydrated when it is surrounded by

water moleculesNaCl(s) Na+(aq) + Cl-(aq)

Na2SO4(s) 2Na+(aq) + SO4-(aq)

Created by C. Ippolito

January 2007

Covalent Electrolytes

• IonizationIonization– ions formed by a reaction between water and

molecular compounds• hydronium cation forms when water gains a H atom

• molecule losing the H atom forms an anionHC2H3O2(l) + H2O H3O+(aq) + C2H3O2

-(aq)

acetic acid hydronium acetate ion

ion

Created by C. Ippolito

January 2007

Acids and Bases• Arrhenius’ AcidArrhenius’ Acid

– a substance that releases H+ ions in water – forming hydronium ions and an anion

HCl(g) + H2O(l) H3O+(aq) + Cl-(aq)

HNO3(l) + H2O(l) H3O+(aq) + NO3-(aq)

H2SO4(l) + H2O(l) 2H3O+(aq) + SO42-(aq)

H2CO3(l) + H2O(l) 2H3O+(aq) + CO32-(aq)

• Arrhenius’ BaseArrhenius’ Base– a substance that releases OH- ions in water – forming hydroxide ions and a cation

NaOH(s) + H2O(l) Na+(aq) + OH-(aq)

Mg(OH)2 + H2O(l) Mg +(aq) + 2OH-(aq)

Ca(OH)2 + H2O(l) Ca +(aq) + 2OH-(aq)

Created by C. Ippolito

January 2007

Neutralization

• Bases mixed with acids result in a reaction known as neutralization.

• Each compound cancels the effect of the other forming water and a salt.

NaOH Na+ + OH-

HCl H+ + Cl-

NaOH + HCl H2O + NaCl

Created by C. Ippolito

January 2007

Brønsted-Lowry Acids and Bases

• Operational Definition– based on directly observable properties

• Conceptual Definition– based on interpretation of observed facts

• Brønsted-Lowry Theory– acid donates a proton – base accepts a proton

Created by C. Ippolito

January 2007

Conjugate Acid-Base Pairs• any acid base reaction:

– one substance donates its most loosely held proton

– another substance accepts that proton

– substances involved in this proton transfer are known as conjugate pairs or conjugate acid-base pairs

• HCl + H2O ↔ H3O+ + Cl-

HCl is the conjugate acid of the base Cl-

H2O is the conjugate base of the acid H3O+

H3O+ is the conjugate acid of the base H2O

Cl- is the conjugate base of the acid HCl

• pair members differ by a proton– in the acid he proton is present (HCl)

– in the base the proton is missing (Cl-)

Created by C. Ippolito

January 2007

Comparing Strengths of Acids and Bases

• Using conjugate acids and base table (p.565)– stronger acids will donate protons to stronger

bases• acids will only donate proton to bases BELOW

them on the table

Created by C. Ippolito

January 2007

Amphoteric Substance

• Amphoteric (Amphiprotic) Substances– can act as either a proton donor or a proton

acceptor• accept protons from strong acids

• donate protons to strong acids