BrnstedLowry Acids and Bases This definition includes a

BrØnsted-Lowry Acids and Bases �This definition includes a lot more substances than Arrhenius acids and bases. �Substances that are only BrØnsted-Lowry acids and bases are not strong, and therefore when they react with each other they reach equilibrium with their conjugates. 1

BrØnsted-Lowry Definition �Acids are any substance that can donate a proton (H+) �Bases are any substance that can accept a proton (H+) HF(g) + H 2 O(l) ↔ H 3 O+(aq) + F-(aq) Acid Base Proton Donor Proton Acceptor 2

Conjugate Pairs �These reversible reactions have an acid and base on both sides �Pairs that differ by only one proton (H+) are called conjugates. HF(g) + H 2 O(l) H 3 O+(aq) +Fˉ(aq) Acid Base Conjugate Acid Conjugate Base 3

�A stronger acid will make a weaker conjugate base �A weaker acid will make a stronger conjugate base. �Same for strong & weak bases. 4

What about H 2 O? Acid or Base? HCl(g) + H 2 O(l) H 3 O+(aq) + Cl-(aq) Acid Base Conjugate Acid Conjugate Base NH 3(g) + H 2 O(l) NH 4+(aq) + OH-(aq) Base Acid Conjugate Base 5

Amphoteric substances �Amphoteric means a substance can either accept a proton (base) or donate a proton (acid). �Water will act as a base when in solution with an acid �Water will act as an acid when in solution with a base �Other amphoteric substances: NH 3 , HSO 4 - , H 2 PO 4 - 6