Acids and BasesSuroviec

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 equilibriumWater ionization constant

Kw = 1.00 X 10-14 at 25.0oC

II. Water Ionization

C. pH scale• One way to describe the concentration of H+ in solution

or the acidity of the solution

D. Determining [H3O+] and [OH-]

pH = 1.00 pH = 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 Ka, Kb and Kw

As acid strength increases Ka increasesAs base strength increases Kb increasesConsider the relation between a conjugate

acid-base pair HB (aq) ⇌ H+ (aq) + B- (aq) KI= Ka of HB

B- (aq) + H2O ⇌ HB (aq) + OH- (aq) KII = Kb of B-

III. Acid/Base reactions

A. Strong Acid/Strong Base

B. Strong – Weak

V. Equilibrium Calculations

A. Determining K from pH

0.015 M HOCN has a pH of 2.67, what is the [H3O+]? What is the Ka 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 Ka of 4.0 x 10-9 what are the equilibrium concentrations of HA, A-, H3O+

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 H2O 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 2.0×10-3M solution of Cod in water.

VI. Polyprotic Acids

Acids capable of donating more than 1 proton