1. CHAPTER 13
Acids
and Bases
13.1 The Chemical Nature of
Acids and Bases

2. What makes an acid an acid? What makes a base a base?
Hydrochloric acid (HCl) is a strong acid in your stomach
The acid in your stomach (HCl)
can burn skin and dissolve metal!
A base from the pancreas (HCO3–) helps to neutralize any acid that leaves the stomach
What makes an acid an acid?
What makes a base a base?
Bicarbonate (HCO3–) ions are produced by the pancreas

3. Higher H+ concentration Lower H+ concentration
From Chapter 4
Higher H+ concentration Lower H+ concentration
The pH scale helps to determine whether a solution is acidic or basic.

4. Neutral solution H2O(l) H+(aq) + OH–(aq) Dissociation of water:
This equilibrium lies heavily on the reactant side
Only 1 out of 550 million water molecules is dissociated into a hydrogen (H+) ion
In neutral water or solution, the concentrations of H+ and OH– are equal
Neutral solution:

5. Acids Acidic solution:
An acid dissolves in water to create more H+ ions than there are in neutral water
Acidic solution:

6. Acids
Acidic solution:

7. Bases NaOH(aq) → Na+(aq) + OH–(aq) Basic solution:
Sodium hydroxide (NaOH) is also known as lye or caustic soda
NaOH(aq) → Na+(aq) + OH–(aq)
A base dissolves in water to create more OH– ions than there are in neutral water
Basic solution:

8. Bases
Basic solution:

9. Bases Potassium hydroxide (KOH) is used in alkaline batteries
A base dissolves in water to create more OH– ions than there are in neutral water
An alkaline substance is a salt of a group 1 or group 2 metal that dissolves in water to make a base.

10. Arrhenius theory
More H+ ions
More OH– ions

11. The hydronium ion
The whole subject of acids and bases has to do with the extraordinary chemical power of the H+ ion, the “naked proton.”
Hydronium ion
(hydrated proton)
H+ is powerful because it has
no electrons!
When we talk about H+ in water, we’re really talking about H3O+

12. Ammonia is a proton acceptor so it is a base
The whole subject of acids and bases has to do with the extraordinary chemical power of the H+ ion, the “naked proton.”
(aq)
NH3 + H2O
NH OH–
Ammonia is a proton acceptor so it is a base

13. Nitric acid is a proton donor
The whole subject of acids and bases has to do with the extraordinary chemical power of the H+ ion, the “naked proton.”
HNO3 → H+ + NO3– (aq)
Nitric acid is a proton donor
It is indeed an acid

14. Acids and bases always act in pairs called conjugate acid-base pairs!
A proton that is donated by one chemical (an acid)
must be accepted by another chemical (a base)
Acids and bases always act in pairs called conjugate acid-base pairs!

15. Acid-base pairs

16. Acid-base pairs NH3 is the conjugate base of NH4+
NH4+ is the conjugate acid of NH3

17. Acid-base pairs HCl is the conjugate acid of H3O+
H3O+ is the conjugate base of HCl

18. Water can act as either an acid or a base!
NH3 + H2O NH OH–
H+ donor
(acid)
Water can act as either an acid or a base!
HCl + H2O H3O+ + Cl–
H+ acceptor
(base)
amphoteric: a substance that can act as either an acid or a base under different circumstances.

19. Identifying acids HCl(aq) → H+(aq) + Cl–(aq)
hydrochloric acid
The H+ that
gets donated is written first
H2C6H6O6(aq) → 2H+(aq) + C6H6O6–(aq)
ascorbic acid (vitamin C)

20. Identifying acids HCl(aq) → H+(aq) + Cl–(aq)
1 M
A strong acid dissociates completely
A weak acid dissociates only partially
H2C6H6O6(aq) → 2H+(aq) + C6H6O6–(aq)
1 M
< 0.02 M

21. The OH group at the end reminds chemists that a chemical is a base
Identifying bases
The OH group at the end reminds chemists that a chemical is a base
Ca(OH)2(aq) → Ca2+(aq) + 2OH–(aq)
calcium hydroxide
Not all bases have an OH group!

22. A strong base dissociates completely
Identifying bases
Ca(OH)2(aq) → Ca2+(aq) + 2OH–(aq)
1 M
2 M
A strong base dissociates completely
KOH(aq) → K+(aq) + OH–(aq)
1 M

23. Identifying bases NH3(aq) + H2O(l) NH4+(aq) + OH–(aq) 1 M ~ 0.004 M
A weak base yields much less than 1 OH– ion per molecule of base in solution.
For example, 1 mole of ammonia (NH3) produces about moles of OH– ions.

24. Arrhenius: Brøndsted-Lowry: pH range: [H+] and [OH–]: Acids Bases
produce H+ ions in aqueous solutions
produce OH– ions in aqueous solutions
donate H+ ions
accept H+ ions
Arrhenius:
Brøndsted-Lowry:
pH < 7
pH > 7
[H+] > [OH–]
[H+] < [OH–]
pH range:
[H+] and [OH–]:
The whole subject of acids and bases has to do with the extraordinary chemical power of the H+ ion, the “naked proton”
Water can act as either an acid or a base

25. HCl(aq) → H+(aq) + Cl–(aq)
Strong:
Complete dissociation
HCl(aq) → H+(aq) + Cl–(aq)
1 M
Acids
1 M
< 0.02 M
H2C6H6O6(aq) → 2H+(aq) + C6H6O6–(aq)
Weak:
Partial dissociation

26. HCl(aq) → H+(aq) + Cl–(aq)
Strong:
Complete dissociation
HCl(aq) → H+(aq) + Cl–(aq)
1 M
Acids
1 M
< 0.02 M
H2C6H6O6(aq) → 2H+(aq) + C6H6O6–(aq)
Weak:
Partial dissociation
Strong:
Complete dissociation
Ca(OH)2(aq) → Ca2+(aq) + 2OH–(aq)
1 M
2 M
Bases
Weak:
Partial dissociation
1 M
~ M
NH3(aq) + H2O(l) NH4+(aq) + OH–(aq)