Chapter 16: Acids and Bases Overview

Arrhenius Acid

A substance that dissociates in water to produce hydrogen ions, H+.

Arrhenius Base

A substance that dissociates in water to produce hydroxide ions, OH-.

Brønsted-Lowry Acid

H+ ion donor.

Brønsted-Lowry Base

H+ ion acceptor.

Conjugate Acid-Base Pairs

Differ from each other only by the presence or absence of a proton (H+).

Strong Acid

Completely ionized.

Weak Acid

Partially ionized.

Strong Base

Completely dissociate in solution.

Weak Base

Do not completely dissociate in solution.

Percent Dissociation

The ratio of the amount of acid that dissociates to the initial concentration of the acid.

pH Scale

A logarithmic scale used to specify the acidity or basicity of an aqueous solution.

Dissociation of Water

The process by which water molecules split into hydrogen ions and hydroxide ions.

Acid Strength

Determined by the degree of ionization in solution.

Base Strength

Determined by the degree of dissociation in solution.

Alkaloid

A plant product that is alkaline and often poisonous.

Conjugate Acid

The species formed when a base accepts a proton (H+).

Conjugate Base

The species formed when an acid donates a proton (H+).

Equilibrium in Weak Acids

The state where the rate of the forward reaction equals the rate of the reverse reaction.

Ka

The acid dissociation constant, a measure of the strength of an acid in solution.

Monoprotic Acid

An acid that can donate only one proton (H+) per molecule.

Polyprotic Acid

An acid that can donate more than one proton (H+) per molecule.

Hydronium Ion (H3O+)

The ion formed when a water molecule gains a proton (H+).

Neutralization Reaction

A chemical reaction in which an acid and a base react to form water and a salt.

Polyatomic(oxo) acids

Greater number of oxygen atoms in anion provides greater stability due to delocalization of the negative charge over more electronegative atoms.

Oxidation Number

The greater the number of oxygen atoms, the stronger the acid.

Electronegativity

Relative ability of an atom to attract electrons in a bond to itself.

Bond Polarity

For binary acids in the same period, bond polarity is more important than bond strength.

Bond Strength

For binary acids of the same group, bond strength is more important than bond polarity.

Autoionization of Water

H2O(ℓ) ⇌ H+(aq) + OH-(aq)

[H3O+] and [OH-] at 298 K

In absence of other acids or bases: [H3O+] = [OH-] = 1 × 10-7 M.

Kw

[H3O+] x [OH-] = 1 × 10-14.

Log form of Kw

-log(Kw)= -log([H+] [OH-]).

pH and pOH relationship

14.00 = pH + pOH.

pH of Weak Acids

Using Ka equation: If pH is known, can calculate Ka; if Ka is known, solve equilibrium problem to calculate [H+] and pH.

Percent Ionization

% Ionization = (x100) for the reaction HNO2(aq) + H2O(l) ⇌ H3O+(aq) + NO2-(aq).

% Ionization trend

% ionization decreases as [acid]o increases.

pH of Weak Bases

To calculate pH: Obtain [OH-] at equilibrium, use Kw relationship.

Finding the Equilibrium Constant from pH

A 0.100 M weak acid (HA) solution has a pH of 4.25. Find Ka for the acid.

pH calculation from pH

pH = -log[H3O+]; [H3O+] = 5.6 × 10-5 M.

Equilibrium concentrations

For most weak acids, the initial and equilibrium concentrations of the weak acid (HA) are equal because the amount that ionizes is usually very small compared to the initial concentration.

pH of Very Dilute Solutions

pH of 1.0 × 10-8 M HCl = ?.

Problem 4

Calculate and compare [H+] and pH for a 0.10 M solution of HClO4 and a 0.10 M solution of HClO (Ka = 2.9 × 10-8).

Problem 5

What are the [H+] and [OH-] in household ammonia, an aqueous solution that has a pH of 11.70?

Problem 6

Calculate the percent ionization for 1.28 M HCN and 0.015 M HCN solutions. Calculate the pH of both solutions. Ka = 4.9 × 10-10.

Problem 7

Calculate and contrast [OH-] in 0.20 M LiOH and 0.20 M NH3 (Kb = 1.76 × 10-5). What are the pH of each solution?

[H+]

1.0 x 10-8 + 9.5 x 10-8 = 1.05 × 10-7 M

pH

Calculated as -log([H+])

Ka1

The acid dissociation constant for the first ionization of a polyprotic acid, typically larger than Ka2.

Ka2

The acid dissociation constant for the second ionization of a polyprotic acid.

pH of 0.100 M sulfuric acid

[H+] = 0.100 M + 0.010 M = 0.11 M; pH = 0.96

Carbonic Acid

Calculate the pH of 0.10 M solution with Ka1 = 4.3 × 10-7 and Ka2 = 4.7 × 10-11.

Neutral Salt

Example: NaCl

Basic Salt

Example: NaF; dissociates into Na+(aq) and F-(aq).

Acidic Salt

Example: NH4Cl; dissociates into NH4+(aq) and Cl-(aq).

Weak Acids

Cations of small, highly charged metals are weakly acidic.

Classification of NH4F

NH4F salt solution is acidic.

Piperidine

An amine with Kb = 1.3 x10-3; calculate Ka for C5H11NH+.

pKa for formic acid

Value is 3.74; calculate pKb for the formate ion (HCO2-).

pH of sodium acetate

Calculate using Ka for acetic acid.

pH of ammonium nitrate

Calculate using Kb for ammonia.

pH of sodium benzoate solution

0.010 M solution; Kb (C7H5O2-) = 1.5 × 10-10.

pH of NaCl

0.1 M NaCl solution has a pH of 7.0.

Lewis Base

Substance that donates a lone pair of electrons.

Lewis Acid

Substance that accepts a lone pair of electrons.

Coordinate covalent bonds

Bonds formed when electron pairs are donated by the Lewis base.