Acid and Bases¶

Brønsted-Lowry Theory of Acid-Base Reactions¶

An acid reacts with a base by giving the base an H⁺
An acid must has an H bonded to an electronegative atom (N, O, F, S, Cl, Br, I (often O))
A base must have a lone pair of electrons to accept the H⁺

HBr + NH₃ -> Br^- + NH₄⁺
HBr: acid NH₃: base

Acids react with water by giving H⁺ to water (water acts like a base)
HCl(aq) + H₂O(l) -> Cl^~(aq) + H₃O⁺(aq)

Base react with water by accepting an H⁺ from water (water acts like acid)
NH₂^-(aq) + H₂O(l) -> NH₃(aq) + OH^-(aq)

Conjugate Acid and Conjugate Base¶

The product of an acid-base reaction is also an acid and a base.

Types of Acids and Bases¶

Binary Acid (HX)¶

H is attached to an electronegative atom but not Oxygen
Strength increases down a group (increase of atomic radius)
Within a group, strength increases to the right (increase of electronegativity)

Oxoacid¶

Acids that have oxygen atoms bonded to acidic hydrodens.

Strength increases when having more resonace structures
Strength increases when having more oxygen atoms (more electronegative)

Organic Acids and Bases¶

Strong and Weak Acids and Bases¶

Acids or bases are labeled as strong or weak based on whether the reaction with water goes to completion.

Conjugate base of a strong acid is very weak
Conjugate base of a weak acid is weak
Conjugate acid of a strong base is very weak
Conjugate acid of a weak base is weak

Anion Stability¶

Acid strength depends on the stability of its conjugate base (anion).

Stable (weak) conjugate base -> strong acid

Increase with the size of the atom
Increase if resonace structures can distribute the charge
Increase with the electronegativitry of the atom carrying the charge and the atoms around it

Lists of Acids and Bases¶

Should remember:

Strong Acid	Name
HCl	Hydrochloric acid
HBr	Hydrobromic acid
HI	Hydroiodic acid
HNO₃	Nitric acid
H₂SO₄	Sulfuric acid
HClO₄	Perchloric acid
HClO₃	Chloric acid

Don't need to remember:

Dissociation Constants¶

Name	Symbol	Unit
Acid ionization constant (stronger the acid, higher the value)	$K_a$	-
Base ionization constant	$K_b$	-
Water ionization constant	$K_w=1.0\times 10^{-14}$	-

Equation	Explain
$K_w=1.0\times 10^{-14}=[H_3O^+][OH^-]=K_a\times K_b$
$K_a = \frac{[H_3O^+][A^-]}{[HA]}$	This cauculates the $K_a$ for HA (aq) + H₂O (l) <-> H₃O⁺ (aq) + A^- (aq)
$K_b = \frac{[HB^+][OH^-]}{[B]}$	This cauculates the $K_b$ for B (aq) + H₂O (l) <-> HB⁺ (aq) + OH^- (aq)
$pH=-log[H_3O^+]$
$[H_3O^+]=10^{-pH}$
$pOH=-log[OH^-]$
$[OH^-]=10^{-pOH}$
$pH+pOH=14$

Autoionization of water¶

Amphiprotic compound: compound that can act as either an acid or a base (e.g. water)

H₂O (l) + H₂O (l) <-> H₃O⁺ (aq) + OH^- (aq)

Last update: December 8, 2021
Created: September 19, 2021