1. Acids & Bases
Chapters 20 & 21

2. Properties of Acids & Bases
React with metals
Taste sour
Bases:
Taste bitter
Feel slippery

3. Chemical Composition
Acids produce Hydrogen ions (H+) in aqueous solution.
Ex: HCl, H2SO4, HNO3
Bases produce Hydroxide ions (OH-) in solution.
Ex: NaOH, KOH, Mg(OH)2

4. Neutralization
Acids & Bases react to form water and a salt (ionic compound).
When combined in the correct amounts, all the OH- and H+ ions combine to form water molecules.
The resulting solution is neutral.

5. pH (percent hydrogen) Acids and bases are measured using the pH scale.
Solutions with a pH of 7 are considered neutral (equal # of H+ and OH- ions)

6. Solutions with a pH lower than 7 are acidic as they contain more H+ ions than OH-.
Solutions with a pH above 7 are basic as they contain more OH- ions than H+.

7. The pH scale
pH is a logarithmic scale, similar to the Richter scale used to measure earthquakes.
An acid with a pH of 2 is ten times stronger than a pH 3 solution.
An acid with a pH of 1 is ten times stronger than a pH 2 solution.

8. pH is dependent upon the concentration (molarity) of H+ ions.
pH = -log[H+]
([X] means molarity of X)

9. Examples
Find the pH of a 1.0 x 10-3M solution of HCl. 3
Find the pH of a 2.5 x 10-5M solution of HNO3
4.6

10. [H+] = 10^ (-pH)
Find the [H+] of a solution with a pH of 6.4 = 4.0x10-7 M
Find the [H+] of a solution with a pH of 9.1 = 7.9x10-10 M
Find the [H+] of a solution with a pH of 2.7 = 2.0x10-3 M

11. pOH
pOH is the opposite of pH.
A pH of 7 = pOH of 7
A pH of 8 = pOH of 6
A pH of 6 = pOH of 8
pOH = 14 – pH

12. pOH
pOH = - log[OH-]
What is the pOH of a solution of a 3.4x10-3 M NaOH?
[OH-] = 10^ (-pOH)
What is the [OH-] of a solution with a pOH of 5.5?

13. Acid – Base Indicators
An indicator is a valuable tool for measuring pH b/c it will change color depending on the pH
Page 590 – Figure 20.8
Litmus paper is an indicator

14. Arrhenius Acids & Bases
Arrhenius Acids – contain H+ ion
Arrhenius Base – contain OH- ion
A monoprotic acid has 1 H+
A diprotic acid has 2 H+
A triprotic acid has 3 H+

15. Bronsted Acids & Bases
Bronsted-Lowry Acids: a hydrogen ion donor
Bronsted-Lowry Base: a hydrogen ion acceptor
NH3 (ammonia) is a Bronsted-Lowry base.

16. Conjugate Acids & Bases
A conjugate acid is the particle formed when a base gains an H+ ion
A conjugate base is the particle formed after an acid gives up its H+ ion

17. Lewis Acids & Bases
A Lewis acid can accept a pair of electrons to form a covalent bond
A Lewis base donates a pair of electrons to form a covalent bond

18. Strength of Acids & Bases
A strong acid ionizes completely in solution
A weak acid ionizes only partially in solution
Strong bases dissociate completely in solution

19. This is a neutralization reaction
Acid-Base Reactions
When an acid and a base react, they will neutralize to form water (HOH) and a salt - double displacement reaction
This is a neutralization reaction
HCl + NaOH  HOH + NaCl

20. Titration
The concentration of an acid or base in solution can be determined by a neutralization reaction
An indicator is used to tell when the pH is neutral

21. Steps of Titration
A measured volume of acid of unknown concentration is added to a flask
Indicator is added
Measured volume of base of known concentration is added until a color change occurs

22. Titration Problem
A 25ml soln. of HCl is neutralized by 18ml 1.0M NaOH. What is the concentration of the acid?
M base = 1.0M
Volume of Base = 18mL
Volume of Acid = 25mL

23. Titration Problem cont’d
MaVa = MbVb
M = molarity, V = volume,
a = acid, b= base
(25mL)(Ma)=(18mL)(1.0M)
(Ma) = (18 x 1.0) / (25)
Ma = 0.72M