Acids

1
Acids Bases

• Section 19.1-19.2 Notes

2
Properties of Acids

• Taste sour (eg citric acids, acetic acid)
• React with metals
• Causes blue litmus to turn pink
• Aqueous solutions conduct electricity

3
Properties of Bases

• Taste bitter
• Feel slippery (eg soap)
• Causes pink litmus to turn blue
• Aqueous solutions conduct electricity

4
Ions in solution

• All water solutions contain H OH-
• Acidic solution contains more H
• Basic solution contains more OH-
• Neutral solution contains equal H OH-
• Water undergoes self-ionization
• H2O(l) H2O(l) ? H3O(aq) OH-(aq)
• H3O and H used interchangeable to represent a
  hydrogen ion
• Pure water is neutral b/c H OH-

5
Arrhenius Acids Bases

• Swedish chemist Svante Arrhenius (1887) first
  proposed how acids bases form
• Arrhenius model
• Acids produce H in aq. soln.
• HCl(g) ? H(aq) Cl-(aq)
• Bases produce OH- in aq. soln.
• NaOH(s) ? Na(aq) OH-(aq)
• Shortcoming does not explain all bases (eg
  NH3 base)

6
Brønsted-Lowry Model

• Danish chemist Johannes Brønsted English
  chemist Thomas Lowry proposed more inclusive
  model
• Brønsted-Lowry model
• Acid H donor
• Base H acceptor
• Every Brønsted-Lowry interaction involves
  conjugate acid-base pairs
• Conjugate acid species produced when a base
  accepts H from an acid
• Conjugate base species produced when an acid
  donates H to a base
• HX H2O ? H3O X-
• acid base
  conjugate conjugate
• 
  acid base

7
You try

• Identify the conjugate acid/base pairs in each of
  the following reactions.
• NH4(aq) OH-(aq) ? NH3(aq) H2O(l)
• HBr(aq) H2O(l) ? H3O(aq) Br-(aq)
• Amphoteric substance that can act as both an
  acid and a base
• CO32-(aq) H2O(l) ? HCO3-(aq) OH-(aq)
• HSO4-(aq) H2O(l) ? H3O(aq) SO42-(aq)

8
Monoprotic and Polyprotic Acids

• Monoprotic contains 1 ionizable hydrogen atom
  (HCl)
• Diprotic contains 2 ionizable hydrogen atoms
  (H2SO4)
• Triprotic contains 3 ionizable hydrogen atoms
  (H3PO4)
• Steps for ionization of a polyprotic acid
• H3PO4
• H2Se
• H2SO3

9
Strength of Acids

• Strong acids ionize completely in water (good
  conductors)
• HCl H2O ? H3O Cl-
• Rxn goes to completion
• Denoted by single arrow
• Weak acids ionize only partially in water (p.
  602)
• HC2H3O2 H2O ? H3O C2H3O2-
• Reversible rxn (double arrow)
• Equilibrium established

10
Strength of Bases

• Strong base dissociates entirely into metal
  ions hydroxide ions
• NaOH ? Na OH-
• Weak base ionizes only partially to form
  conjugate acid hydroxide ion
• CH3NH2 H2O ? CH3NH3 OH-