Chapter 15

A C I D S A N D B A S E S S U R O V I E C S P R I N G 2 0 1 4

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 + conjugate acid-base pair is called a 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 10 -14 at 25.0

o C

II. Water Ionization C.

• pH scale One way to describe the concentration of H + acidity of the solution in solution or the

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

pH = 10.50

A. Acid IV. Equilibrium constants   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) B (aq) + H 2 O ⇌ HB (aq) + OH (aq) K I = K a K II = K b of HB 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 [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 10 -9 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