Acid –Base
Theories 19.1
A. Acids
Describing an Acid
 Tastes “sour”
 Common compound in fruits and
vegetables
 corrosive
 Forms electrolytes when in aqueous
solution (ions!)
 Is a molecular compound
Explaining Acid Behavior
 Acids are hydrogen containing
substances, HCl, H2SO4
 But not all hydrogen containing
compounds are acids!!! CH4,
C6H12O6
 Dissociate (ionize) by releasing H+
ions (hydrogen ion or proton) into
solution.
 written as a dissociation Rx
 HCl →H+ + OH-
Acid Formulas
 Acids are ionic compounds where the
cation is H+ (not a metal)
 Anion: Periodic table (how many +/-) and
Memory (polyatomic ions: nitrate,
hydroxide, carbonate, chlorate, sulfate,
phosphate
 Undissociated it is a neutral compound
Acid Formulas
 Example: phosphoric acid
 Made of phosphate and enough H+ to
neutralize it
 Formula of phosphate:
 PO43 Plus 3 H+
 H3PO4
Types of Acids
Contains/releases one ionizable H+ ,
monoprotic acid
 HCl → H+ + ClContains/releases two ionizable H+ ,
diprotic acid
 H2SO4 → 2H+ + SO42Contains/releases three ionizable H+ ,
triprotic acid
 H3PO4 → 3H+ + PO43-
Review Electronegativity
 Increases in this direction
Why do acids release H+?
 H involved in very polar covalent bonds
–attached to a very electronegative
element are released as H+ ions
 Example HCl: Cl is very electronegative
H-Cl --- H+ + Clδ+ δ On the other hand: CH4 weakly polar
molecule: C is not very electronegative,
does not release an H+!!!
What does the H+ do?
 Reacts with H2O to form an hydronium
ion H3O+
a. H+ + H2O → H3O+
Hydrochloric acid
(hydrogen chloride)
 HCl
 Monoprotic acid
H - Cl
 HCl → H+ + Cl-
Nitric Acid
 HNO3
 Monoprotic acid
 HNO3 →H+ + NO3-
Carbonic Acid
 H2CO3
 Diprotic acid
 H2CO3 →2H+ + CO32-
Phosphoric Acid
 H3PO4
 Triprotic acid
 H3PO4 →3 H+ + PO43-
Sulfuric Acid
 H2SO4
 Diprotic acid
 H2SO4→ 2H+ + SO42-
Formulas of Organic AcidsAcids of Hydrocarbons



Example: CH3COOH
Not all hydrogens are released!
Which bonds are high/low polar
very polar
Weak polar
 Monoprotic
Organic Acids have
Carboxyl Groups
 COOH group is called a carboxyl group
 Makes a molecule acidic
 Dissociation:
CH3COOH→CH3COO- + H+
Ethanoic Acid (acetic or
vinegar acid)
 CH3COOH
 monoprotic acid
 CH3COOH→H+ +CH3COO-
B. Describing a Base




Adjective: basic or alkaline
rare in nature/foods
taste bitter
are part of soaps –make surfaces
slippery
 Corrosive, often more dangerous than
acids
 Are part of cleaners, drain openers
 Act as electrolyte if aqueous
Base Formulas
 Normal ionic neutral compound: metal
cation and hydroxide anion (OH-)
 Formula ends with OH
 Name ends with ‘hydroxide’
 NaOH –sodium hydroxide
 Give the formula of Calcium Hydroxide
 Ca(OH)2
Base Behavior
 Dissociation into metal cation and
hydroxide ion, OH A base is a hydroxide donor
 NaOH → Na+ + OH-
Sodium Hydroxide NaOH




Ionic compound
Releases OHNaOH → Na+ + OHOther similar base: KOH (potassium
hydroxide), CsOH, RbOH
Magnesium hydroxide
 Mg(OH)2
 Mg(OH)2 →Mg2+ + 2(OH) Similar are Calcium- or Bariumhydroxide
Ammonia NH3




Exceptional base:
Does not directly release OHInstead breaks water apart
NH3 + H2O → NH4+ + OH-
Testing for Acids and
Bases
 indicator substances that change color
 Litmus paper
 Commercially available test strips
Acids and Bases together
 React with each other
 neutralize
 form a salt of the base cation and the
acid anion and water
HCl + NaOH→ NaCl + H2O
Practice: Carbonic acid reacts with Calcium
hydroxide