14.3 Acid-Base Reactions

POINT > Define conjugate acid-base pairs POINT > Describe strength of acids and bases POINT > Identify amphoteric species POINT > Describe neutralization reactions

POINT > Define conjugate acid-base pairs Recall that Brønsted–Lowry reactions must have a proton donor (acid) and a proton acceptor (base) HCl + H 2 O  H 3 O + + Cl -

A Brønsted–Lowry acid must have a removable (acidic) proton: HCl, H 2 SO 4, CH 3 COOH A Brønsted–Lowry base must have a pair of nonbonding electrons to accept the proton: NH 3, OH - POINT > Define conjugate acid-base pairs

Reactions between acids and bases always yield their conjugate bases and acids. HCl + NH 3  NH Cl - When an acid donates a proton, its conjugate base is formed Cl - is the conjugate base of the acid HCl

POINT > Define conjugate acid-base pairs Reactions between acids and bases always yield their conjugate bases and acids. HCl + NH 3  NH Cl - When an base accepts a proton, its conjugate acid is formed NH 4 + is the conjugate acid of the base NH 3

POINT > Define conjugate acid-base pairs Reactions between acids and bases always yield their conjugate bases and acids. HCl + NH 3  NH Cl - The conjugate acid always has one more proton than its conjugate base

POINT > Define conjugate acid-base pairs Reactions between acids and bases always yield their conjugate bases and acids.

WB CHECK: HF + H 2 O ↔ F - + H 3 O + What is the conjugate base of HF? What is the conjugate acid of H 2 O? What is the conjugate base of H 3 O + ? What is the conjugate acid of F - ?

POINT > Describe strength of acids and bases Strong acids completely dissociate in water: HCl + H 2 O  H 3 O + + Cl - Their conjugate bases are therefore quite weak HCl HBr HI H 2 SO 4 HNO 3 HClO 4 HClO 3 These are the strong acids

POINT > Describe strength of acids and bases Weak acids dissociate only partially in water: CH 3 COOH + H 2 O ↔ H 3 O + + CH 3 COO - Their conjugate bases are stronger bases

POINT > Describe strength of acids and bases The stronger an acid, the weaker its conjugate base The stronger a base, the weaker its conjugate acid The transfer of the proton in acid-base reactions favors the production of the weaker acid and base

POINT > Describe strength of acids and bases The transfer of the proton in acid-base reactions favors the production of the weaker acid and base HCl + H 2 O H 3 O + + Cl - Compare the strengths of the acids (HCl and H 3 O + ) and the bases (H 2 O and Cl - ) using chart p. 459 The hydronium ion and chloride ion are weaker as acid and base respectively, so the arrow points…. 

POINT > Describe strength of acids and bases The transfer of the proton in acid-base reactions favors the production of the weaker acid and base CH 3 COOH + H 2 O H 3 O + + CH 3 COO - Compare the strengths of the acids (acetic acid and H 3 O + ) and the bases (H 2 O and acetate ion) using chart page 459 The acetic acid and water are weaker as acid and base respectively, so the arrow points…. 

WB CHECK: Predict the direction a reaction will take, based on acid and base strength: HBr + H 2 O ? H 3 O + + Br -

WB CHECK: Predict the direction a reaction will take, based on acid and base strength: HBr + H 2 O  H 3 O + + Br - HNO 3 + H 2 O ? H 3 O + + NO 3 -

WB CHECK: Predict the direction a reaction will take, based on acid and base strength: HBr + H 2 O  H 3 O + + Br - HNO 3 + H 2 O  H 3 O + + NO 3 -

As you may have noticed, water can act as an acid or a base. Such particles are called amphoteric: They tend to be weak as acids and weak as bases H2OH2O HCO 3 - HSO 4 - POINT > Identify amphoteric species

POINT > Describe neutralization reactions Strong acids and strong bases react with each other in neutralization reactions The protons released by strong acids combine with hydroxide ions released by strong bases to form water and a salt HCl + NaOH  H 2 O + Na + + Cl -

WB CHECK: Predict the products of the strong acid-strong base reaction: HBr + Mg(OH) 2  ? HNO 3 + KOH  ?

Homework: Read Section 14.3 Pages Section Assessment #1-3 Page 463