Class notes for Chapter 16: Acids and Bases in the class General Chemistry: Macroscopic Investigations and Reaction Principles (CHEM 130) at the University of Michigan. Topics covered include autoionization, acid-base reactions and definitions, and conjugates.
Lecture
●Acid (Arrhenius def): something that produces H+ in an aqueous solution OR donates H+ to a base in a reaction ○General equation: HA(aq) → H+ (aq) + A– (aq)
○In water – H3O+ ■Lewis: H+ (aq) + H–O–H → [H–O–H + another branch]+
●Acidic Hydrogens: can be donated in an aqueous solution to a base
○In acids with many Hs, some may participate in donation as acidic hydrogens and others may not
■EX: Acetic acid HC 2H3O2, only the first H is acidic
○Acidic hydrogens have partial positive charges in polar bonds
●Base (Arrhenius def): produces OH– in aqueous solution
○Generic equation: B(aq) + H 2O (L) → BH+ (aq) + OH– (aq)
●Strong acids and bases dissociate completely, weak acids and bases dissociate partially
○Strong acids/base use normal arrow to represent reaction
■HCl(aq) → H+(aq) + Cl–(aq)
○Weak acids/bases use equilibrium arrow to represent reaction ⇌
■HF(aq) ⇌ H+(aq) + F–(aq)
●Acid (Bronsted-Lowry definition): proton donor
○HCl(aq) + H2O(L) → H3O+ (aq) + Cl– (aq)
■Water accepts proton from H+
●Base (Bronsted-Lowry definition): proton acceptor
○NH3(aq) + H2O (L) ⇌ NH4+(aq) + OH–(aq)
●Conjugate Acid-Base Pair: in a reaction in which there is an acid-base reaction in both directions (one acid and one base), there is a conjugate acid that is a base + H+ and a conjugate base that is an acid – H+
○Acids and bases react to form the conjugates
○EX: Identify the Bronsted-Lowry acid and base and conjugate acid and conjugate
base for the reaction:
C5H5N(aq) + H2O(L) ⇌ C5H5NH+(aq) + OH–(aq)
■Water is the acid (loses a proton) to become OH–
●OH– is the conjugate base
■C5H5N is the base (gains a proton) to become C 5H5NH+
●C5H5NH+ is the conjugate acid
●** SKIP 16.4
●Generic acid dissociation in water:
HA(aq) + H2O(l) ⇌ H3O+(aq) + A– (aq)
○Ka = ([H3O][A–] / [HA]
■HA = generic acid with one acidic proton on the acid molecule
○If you have strong acids, concentration will equal acid concentration
■Eg. if 1.0M HCl (strong acid), then the solution is 1.0M H+
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