Chapter 16: Equilibrium in Acid- Base Systems 16.2a: Bronsted-Lowry Acid-Base Concept

Definition of Acid and Base Bronsted-Lowry Bronsted-Lowry independently created by two scientists around the same time (1923) independently created by two scientists around the same time (1923) looked at how acid/base acted in reactions instead of their properties in aqueous solutions looked at how acid/base acted in reactions instead of their properties in aqueous solutions theoretical definitions based upon proton transfer during a reaction theoretical definitions based upon proton transfer during a reaction

Proton transfer concept Acid: molecule or ion that is a proton (H + ) donor Acid: molecule or ion that is a proton (H + ) donor HCl + H 2 O  H 3 O + + Cl - HCl + H 2 O  H 3 O + + Cl - Base: molecule or ion that is a proton (H + ) acceptor Base: molecule or ion that is a proton (H + ) acceptor NH 3 + H 2 O  NH OH - NH 3 + H 2 O  NH OH -

Bronsted-Lowry concept B-L acid a proton donor; B-L base a proton acceptor B-L acid a proton donor; B-L base a proton acceptor B-L neutralization is a competition for protons from the SA to the SB B-L neutralization is a competition for protons from the SA to the SB B-L rxtn. eqtn. is an eqtn. that shows this transfer of protons from one entity to another B-L rxtn. eqtn. is an eqtn. that shows this transfer of protons from one entity to another

Acids or Bases? C 5 H 5 N C 5 H 5 N base (weak) base (weak) Mg(OH) 2 Mg(OH) 2 base (strong) base (strong) HF HF acid (weak) acid (weak) NH 3 NH 3 base (weak) base (weak) H 2 CO 3 H 2 CO 3 acid (weak) acid (weak) H 2 SO 4 H 2 SO 4 acid (strong) acid (strong) KOH KOH base (strong) base (strong) CH 3 NH 2 CH 3 NH 2 base (weak) base (weak) HC 2 H 3 O 2 HC 2 H 3 O 2 acid (weak) acid (weak) HI HI acid (strong) acid (strong)

Acid – Base Reactions Identify the acids and bases of the following reactions Identify the acids and bases of the following reactions C 6 H 5 NH 2 + H 2 O  C 6 H 5 NH OH - C 6 H 5 NH 2 + H 2 O  C 6 H 5 NH OH - BABABABA HNO 3 + H 2 O  H 3 O + + NO 3 - HNO 3 + H 2 O  H 3 O + + NO 3 - ABABABAB HCH 3 COO + H 2 O  H 3 O + + CH 3 COO - HCH 3 COO + H 2 O  H 3 O + + CH 3 COO - A B A B

Acid-Base Reactions Amphoteric Substances Amphoteric Substances proper term used in B-L reactions proper term used in B-L reactions a substance that can react as either acid or base depending on what they are mixed with a substance that can react as either acid or base depending on what they are mixed with example: water, HSO 4 - example: water, HSO 4 - Amphiprotic Amphiprotic incorrect term to use with B-L rxtns. incorrect term to use with B-L rxtns. refers to an entity (ion or molecule) refers to an entity (ion or molecule)

Amphoteric Water Water as an acid (proton donor) Water as a base (proton acceptor)

Conjugate Acid-Base Pairs Conjugate acids and bases are always created by a B-L reaction (as products) Conjugate base Conjugate base an acid that has lost a H + an acid that has lost a H + missing a hydrogen missing a hydrogen ex: H 2 PO 4 -, OH -, Cl - ex: H 2 PO 4 -, OH -, Cl - Conjugate acid Conjugate acid a base that has gained a H + a base that has gained a H + has an extra hydrogen has an extra hydrogen NH 4 +, C 6 H 5 NH 3 +, H 3 O + NH 4 +, C 6 H 5 NH 3 +, H 3 O + A pair of substances with formulas that differ only by a proton is called a conjugate acid-base pair

Identify the parts of these reactions C 6 H 5 NH 2 + H 2 O  C 6 H 5 NH OH - C 6 H 5 NH 2 + H 2 O  C 6 H 5 NH OH - base acid CA CB HNO 3 + H 2 O  H 3 O + + NO 3 - HNO 3 + H 2 O  H 3 O + + NO 3 - acidbase CACB HCH 3 COO + H 2 O  H 3 O + + CH 3 COO - HCH 3 COO + H 2 O  H 3 O + + CH 3 COO - acidbase CACB NH 3 + H 2 O  NH OH - NH 3 + H 2 O  NH OH - base acid CA CB

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