Chapter 16: Chapter 16: Equilibrium in Equilibrium in

Acid-Base SystemsAcid-Base Systems

16.2a: Bronsted-Lowry Acid-Base 16.2a: Bronsted-Lowry Acid-Base ConceptConcept

Definition of Acid and BaseDefinition of Acid and Base

Bronsted-LowryBronsted-Lowry independently created by two scientists independently created by two scientists

around the same time (1923)around the same time (1923) looked at how acid/base acted in reactions looked at how acid/base acted in reactions

instead of their properties in aqueous instead of their properties in aqueous solutionssolutions

theoretical definitions based upon proton theoretical definitions based upon proton transfer during a reactiontransfer during a reaction

Proton transfer conceptProton transfer concept

Acid: molecule or ion that is a proton (HAcid: molecule or ion that is a proton (H++) ) donordonor

HCl + HHCl + H22O O H H33OO++ + Cl + Cl--

Base: molecule or ion that is a proton (HBase: molecule or ion that is a proton (H++) ) acceptoracceptor

NHNH33 + H + H22O O NH NH44++ + OH + OH--

Bronsted-Lowry conceptBronsted-Lowry concept

B-L acid a proton donor; B-L base a B-L acid a proton donor; B-L base a proton acceptorproton acceptor

B-L neutralization is a competition B-L neutralization is a competition for protons from the SA to the SBfor protons from the SA to the SB

B-L rxtn. eqtn. is an eqtn. that shows B-L rxtn. eqtn. is an eqtn. that shows this transfer of protons from one this transfer of protons from one entity to anotherentity to another

Acids or Bases?Acids or Bases?

CC55HH55NN base (weak)base (weak)

Mg(OH)Mg(OH)22

base (strong)base (strong) HFHF

acid (weak)acid (weak)

NHNH33

base (weak)base (weak)

HH22COCO33

acid (weak)acid (weak)

HH22SOSO44

acid (strong)acid (strong) KOHKOH

base (strong)base (strong)

CHCH33NHNH22

base (weak)base (weak)

HCHC22HH33OO22

acid (weak)acid (weak) HIHI

acid (strong)acid (strong)

Acid – Base ReactionsAcid – Base Reactions Identify the acids and bases of the Identify the acids and bases of the

following reactionsfollowing reactions

CC66HH55NHNH22 + H + H22O O C C66HH55NHNH33++ + OH + OH--

BB AA HNOHNO33 + H + H22O O H H33OO++ + NO + NO33

--

AA BB HCHHCH33COO + HCOO + H22O O H H33OO++ + CH + CH33COOCOO--

AA B B

Acid-Base ReactionsAcid-Base Reactions

Amphoteric SubstancesAmphoteric Substances proper term used in B-L reactionsproper term used in B-L reactions a a substancesubstance that can react as either that can react as either

acid or base depending on what they acid or base depending on what they are mixed withare mixed with

example: water, HSOexample: water, HSO44--

AmphiproticAmphiprotic incorrect term to use with B-L rxtns.incorrect term to use with B-L rxtns. refers to an refers to an entityentity (ion or molecule) (ion or molecule)

Amphoteric WaterAmphoteric Water

Water as an acid (proton donor)

Water as a base (proton acceptor)

Conjugate Acid-Base Conjugate Acid-Base PairsPairs

Conjugate acids and bases are always Conjugate acids and bases are always created by a B-L reaction (as products)created by a B-L reaction (as products)

Conjugate baseConjugate base an acid that has lost a an acid that has lost a

HH++

missing a hydrogenmissing a hydrogen ex: Hex: H22POPO44

--, OH, OH--, Cl, Cl--

Conjugate acidConjugate acid a base that has gained a a base that has gained a

HH++

has an extra hydrogenhas an extra hydrogen NHNH44

++, C, C66HH55NHNH33++, H, H33OO++

A pair of substances with formulas that differ only by a proton is called a conjugate acid-base pair

Identify the parts of these Identify the parts of these reactionsreactions

CC66HH55NHNH22 + H + H22O O C C66HH55NHNH33++ + OH + OH--

basebase acid acid CA CB CA CB HNOHNO33 + H + H22O O H H33OO++ + NO + NO33

--

acidacid basebase CA CA CBCB HCHHCH33COO + HCOO + H22O O H H33OO++ + CH + CH33COOCOO--

acidacid basebase CA CA CBCB NHNH33 + H + H22O O NH NH44

++ + OH + OH--

base acidbase acid CA CA CB CB

HomeworkHomework

Textbook p724 #1-6Textbook p724 #1-6 Textbook p726 #7Textbook p726 #7 LSM 16.2A summary 1LSM 16.2A summary 1