ACIDS and BASES

1
ACIDS and BASES

• Chapter 18

2
Acids and Bases An Introduction

• Acidic solution contains more hydrogen ions
  than hydroxide ions. HgtOH-
• Basic solution contains more hydroxide ions
  than hydrogen ions. OH-gtH
• Arrhenius model states that an acid is a
  substance that contains hydrogen and ionizes to
  produce hydrogen ions in aqueous solution.
• HCl ? H(aq) Cl-(aq)
• NaOH ? Na(aq) OH-(aq)
• Bronsted-Lowry model an acid is a hydrogen-ion
  donor and a base is a hydrogen-ion acceptor.
• HX(aq) H2O(l) ?? H3O(aq) X-(aq)

3
Acids and Bases

• Conjugate acid the species produced when a base
  accepts a hydrogen ion from an acid.
• Conjugate base the species that results when an
  acid donates a hydrogen ion to a base.
• Conjugate acid-base pair consists of two
  substances related to each other by the donating
  and accepting of a single hydrogen ion.
• Amphoteric substances that can act as both
  acids and bases. (H2O)
• Anhydrides oxides that become acids or bases by
  adding the elements contained in water.
• CO2(g) H2O(l) ? H2CO3(aq)
• CaO(s) H2O(l) ? Ca2(aq) 2OH-(l)

4
Strengths of Acids and Bases

• Strong Acids acids that ionize completely.
• Produce the maximum number of ions, they are good
  conductors of electricity. HClO4, HNO3, HI
• HCl(aq) H2O(l) ? H3O(aq) Cl-(aq)
• Weak Acids acids that ionizes only partially in
  dilute aqueous solutions.
• Strong Acids produce a weak conjugate base.
• Weak Acids produce a strong conjugate base.

5
Strengths of Acids and Bases

• Acid ionization constant (Ka) the value of the
  equilibrium constant expression for the
  ionization of a weak acid.
• Table 19-2 pg.605
• Example Write ionization equations and acid
  ionization constant expressions for the following
  acids.
• HClO2 HNO2
• HClO2(aq) H2O(l) ?? H3O(aq) ClO-(aq)
• KaH3OClO2-/HClO2
• HNO2(aq) H2O(l) ?? H3O(aq) NO2-(aq)
• KaH3ONO2-/HNO2

6
Strengths of Acids and Bases

• Strong Bases dissociate entirely into metal
  ions and hydroxide ions.
• Examples metallic hydroxides, sodium hydroxide
• NaOH(s) ? Na(aq) OH-(aq)
• Weak Bases ionizes only partially in dilute
  aqueous solution to form the conjugate acid of
  the base and hydroxide ion.
• CH3NH2(aq) H2O(l) ?? CH3NH3(aq) OH-(aq)
• Strong bases produce a weak conjugate acid
• Weak bases produce a strong conjugate acid

7
Strengths of Acids and Bases

• Base ionization constant (Kb)- the value of the
  equilibrium constant expression for the
  ionization of a base.
• Table 19-4 pg.607
• Example Write the ionization equations and base
  ionization constant expressions for the following
  bases.
• Hexylamine (C6H13NH2) Propylamine (C3H7NH2)
• C6H13NH2(aq) H2O(l) ?? C6H13NH3(aq) OH-(aq)
• KbC6H13NH3OH-/C6H13NH3
• C3H7NH2(aq) H2O(l) ?? C3H7NH3(aq) OH-(aq)
• KbC3H7NH3OH-/C3H7NH2

8
What is pH?

• Concentration of pure water.
• KeqH2O Kw HOH- (1.0x10-7)(1.0x10-7)
• Kw1.0x10-14
• Ion product constant for water the value of the
  equilibrium constant expression for the
  self-ionization of water.
• Example Calculate H or OH-. Is the solution
  acidic, basic, or neutral?
• H 1.0x10-13M
• OH- 1.0x10-7M

9
What is pH?

• pH the negative logarithm of the hydrogen ion
  concentration.
• pH -logH
• pOH negative logarithm of the hydroxide ion
  concentration.
• pOH -logOH-
• pH pOH 14.00

10
What is pH?

• Examples Calculate the pH or pOH of solutions
  having the following ion concentrations.
• H 1.0x10-2M
• OH- 8.2x10-6M
• OH- 6.5x10-4M
• H 0.025M

11
What is pH?

• Calculating ion concentrations from pH pOH
• Antilog(-pH) H
• Antilog(-pOH) OH-
• Example Calculate H and OH-.
• pH 2.37
• pH 11.05
• Example Calculate the pH of the following.
• 1.0M HI
• 0.050M HNO3
• 1.0M KOH

12
What is pH?

• Example Calculate the Ka for the following acid
  using the given information.
• 0.0400M solution of HClO2, pH 1.80

13
Neutralization

• Neutralization reaction a reaction in which an
  acid and a base react in aqueous solution to
  produce a salt and water.
• Double-replacement reaction
• Salt an ionic compound made up of a cation from
  a base and an anion from an acid.
• NaOH HCl ? NaCl H2O
• base acid ? salt water

14
Neutralization

• Example Write a balanced formula equation for
  the following acid-base neutralization reaction.
• Nitric acid and cesium hydroxide
• Hydrobromic acid and calcium hydroxide

15
Acid-base Titration

• Titration a method for determining the
  concentration of a solution by reacting a known
  volume of the solution with a solution of know
  concentration.
• Acid-base indicators chemical dyes whose colors
  are affected by acidic and basic solutions.
• End point point at which the indicator used in
  a titration changes color.

16
Acid-base reactions

• Salt hydrolysis the anions of the dissociated
  salt accept hydrogen ions from water or the
  cations of the dissociated salt donate hydrogen
  ions to water.
• Buffers solutions that resist changes in pH
  when limited amounts of acid or base are added.
• Buffer capacity amount of acid or base a buffer
  solution can absorb without a significant change
  in pH.