ACIDS AND BASES SUROVIEC SPRING 2014 Chapter 15

I. Definitions of Acids/Bases A. Arrhenius  Acid: something that releases H + in water  Base: something that releases OH - in water B. Brønsted-Lowry  Acid: substance that donates a proton  Base: substance that accepts a proton

C.Monoprotic vs. Polyprotic Monoprotic  acid – only has 1 proton to donate  base – only can accept 1 proton Polyprotic  acid – can donate several protons  Base – can accept several protons

D.Conjugate Acid-Base Pairs A pair of compounds that differ by the presence of one H + is called a conjugate acid-base pair Every reaction between a Brønsted acid and Brønsted base involves H + transfer and has 2 conjugate acid-base pairs

II. Water Ionization A. Water equilibrium Water ionization constant K w = 1.00 X at 25.0 o C

II. Water Ionization C. pH scale One way to describe the concentration of H + in solution or the acidity of the solution

D. Determining [H 3 O + ] and [OH - ] pH = 1.00pH = 10.50

IV. Equilibrium constants A. Acid Acids and bases are either:  strong electrolytes: completely dissociates  weak electrolytes: ionizes very little in water Ionization constants measure extent of ionization:  K>1: ionize extensively, strong acid/base  K<1: does not ionize extensively, weak acid/base

B. Bases

C. Compare Acid/Base strength Look at the pKa value and compare to the acid strength

D. Relationship between K a, K b and K w As acid strength increases Ka increases As base strength increases Kb increases Consider the relation between a conjugate acid-base pair  HB (aq) ⇌ H + (aq) + B - (aq) K I = K a of HB  B - (aq) + H 2 O ⇌ HB (aq) + OH - (aq) K II = K b of B -

III. Acid/Base reactions A. Strong Acid/Strong Base

B. Strong – Weak

V. Equilibrium Calculations A. Determining K from pH M HOCN has a pH of 2.67, what is the [H 3 O + ]? What is the K a of HOCN?

B. Determining the Equilibrium Concentrations and pH from Ka A. Weak acid ionization Given a weak acid (HA) concentration of 0.040M with a K a of 4.0 x what are the equilibrium concentrations of HA, A -, H 3 O +

C. 5% rule Codeine (Cod) is a powerful and addictive painkiller. It is also a weak base.  Write the reaction of weak base Cod with H 2 O  If the Ka of Hcod (the weak conjugate acid) is 1.2×10 -8, what is the Kb of Cod?  Find the pH of a 2.0×10 -3 M solution of Cod in water.

VI. Polyprotic Acids Acids capable of donating more than 1 proton