CHAPTER 19 ACIDS, BASES, AND SALTS
ACIDS AND BASESAcids:Taste sourElectrolytes Change indicator
colorReact with metals →
H2 gas
Bases:Taste bitterElectrolytes Change indicator
color
ARRHENIUS ACIDS AND BASESAcids: hydrogen-containing compounds that ionize to
yield hydrogen ions (H+) in aqueous solutionBases: ionize to yield hydroxide ions (OH-) in aqueous
solution
Monoprotic acid: 1 H+ i.e. HNO3, HCl,Diprotic acid: 2 H+ i.e. H2SO4, H2CO3Triprotic acid: 3 H+ i.e. H3PO4
In water, H+ joins water molecules to form hydronium ions (H3O+)
BRØNSTED-LOWRY ACIDS AND BASESAcid: Hydrogen donorBase: Hydrogen acceptor (broader than Arrhenius’
definition) includes bases such as ammonia (NH3) and sodium
carbonate (Na2CO3)
Water can be an acid (donate H+) or base (accept H+)
BRØNSTED-LOWRY ACIDS AND BASESConjugate acid: formed when the base gains a hydrogen
ionConjugate base: remains after an acid loses a hydrogen
ion
NH3 (aq) + H2O (l) ⇌ NH4+ (aq) + OH- (aq)
base acid conj. acid conj. baseConjugate acid-base pair: two molecules related by the
gain/loss of one hydrogen ion
HCl + H2O ⇌ H3O+ + Cl-
acid base conj. acid conj. base
LEWIS ACIDS AND BASESAcid: accepts a pair of electrons during a reactionBase: donate a pair of electrons during a reaction
HYDROGEN IONS FROM WATER
Self-ionization of water
Neutral solution: [H+] = [OH-]Water is neutral with 1 x 10-7M H+ and 1 x 10-7M OH-
HYDROGEN IONS FROM WATERAcidic solution: [H+] > [OH-] [H+] > 1 x 10-7M
Basic solution: [H+] < [OH-] [H+] < 1 x 10-7M
pH is the negative logarithm of the hydrogen-ion concentration pH= –log[H+]
pH <7.0 is acidicpH > 7.0 is basic
THE pH CONCEPT
• Acid-Base Indicators• Used for initial measurement, small samples• Indicator is a weak acid or base that dissociates in a
known pH range and changes color• pH range may change with temperature• Colored substances may be difficult to read
MEASURING pH
• pH Meters• Accurate within 0.01 pH units• Used in hospitals and waste treatment• Results not affected by color or cloudiness of the
sample
MEASURING pH
STRONG AND WEAK ACIDS AND BASESClassified by the degree to which they ionize in waterStrong acids/bases: ionize completely in waterWeak acids/bases ionize only slightly in waterAcid dissociation constant (Ka)Base dissociation constant (Kb)
ACID-BASE REACTIONSAcids and bases react to form a salt and water
This is called a neutralization reaction
TITRATIONTitration: process of adding a measured amount of a
solution of known concentration to a solution of unknown concentration1. Measured volume of unknown concentration acid is
added to a flask.2. Add several drops of indicator to flask, swirl.3. Measured volumes of base of known concentration
are mixed in until indicator just barely changes color.
TITRATIONNeutralization occurs when moles H+ = moles OH-
This is called the equivalence pointIndicator chosen for titration must change color at
or near the equivalence pointEnd point: point at which the indicator has changed
color
Salt Hydrolysis
Ion of a salt in solution either donates or removes a hydrogen ion from water
Acidic salts: cation releases H+ to waterBasic salts: anion removes H+ from water
BUFFERSBuffer: a solution in which the pH remains fairly
constant with addition of some acid or basemade of a weak acid and one of its salts or a weak
base and one of its salts
Buffer Capacity
Amount of acid or base that can be added to a buffer system without changing pH significant
The more weak acid/base and salt in solution, the greater the buffer capacity