Acids
Arrhenius acids
• produce H+ ions in water.
• are electrolytes.
• have a sour taste.
• turn litmus red.
• neutralize bases.
1
Note acid name endings: -ic (if anion was –ide or –ate)
-ous (if anion was –ite)
2
Acids you need to know
by name and formula (see Syllabus)
•
•
•
•
•
•
•
•
Hydrochloric acid = HCl
Hydrofluoric acid = HF
Sulfuric acid = H2SO4
Dihydrogen phosphate ion = H PO Phosphoric acid = H3PO4 Monohydrogen phosphate ion = HPO 2Bicarbonate
ion
=
HCO
Carbonic acid = H2CO3
Nitric acid = HNO3
Acetic acid = HC2H3O2 = CH3COOH
Hydrogen sulfide = H2S
2
4
4
3
3
Bases
Arrhenius bases
• produce OH− ions
(hydroxide ions) in water.
• taste bitter or chalky.
• are electrolytes.
• feel soapy and slippery.
• neutralize acids.
4
Hydroxides are typical Arrhenius Bases
5
BrØnsted-Lowry Acids and Bases
According to the BrØnsted-Lowry theory,
• acids donate a proton (H+).
• bases accept a proton (H+).
6
NH3, a BrØnsted-Lowry Base
In the reaction of ammonia and water,
• NH3 is the base that accept H+.
• H2O is the acid that donates H+.
7
8
NH3
9
Comparing Acids and Bases
Identify compound as acid or based by given property and formula.
10
Learning Check
Identify each as a characteristic of an
A) acid
or
B) base.
1.
2.
3.
4.
5.
has a sour taste
produces OH- in aqueous solutions
has a chalky taste
is an electrolyte
produces H+ in aqueous solutions
11
Strengths of Acids and Bases
12
Strong and Weak Acids
• In an HCl solution, the
strong acid HCl
dissociates 100%.
• A solution of the weak
acid CH3COOH
contains mostly
molecules and a few
ions.
13
• A strong acid completely ionizes (100%) in aqueous
solutions. Is a strong electrolyte.
HCl(g) + H2O(l)
H3O+ (aq) + Cl− (aq)
14
A weak acid dissociates only slightly in water to form a
few ions in aqueous solutions.
H2CO3(aq) + H2O(l)
H3O+(aq) + HCO3− (aq)
15
16
Strong Bases
Strong bases
• are formed from metals of
Groups 1A (1) and 2A (2).
• include LiOH, NaOH, KOH, and
Ca(OH)2.
• dissociate completely in water.
KOH(s)
K+(aq) + OH−(aq)
17
Weak Bases
Weak bases
• are most other bases.
• dissociate only slightly in water.
• form only a few ions in water.
NH3(g) + H2O(l)
NH4+(aq) + OH−(aq)
18
Ionization of Water
H2O + H2O
H3O+ + OH-
19
Pure Water is Neutral
In pure water,
• the ionization of water
molecules produces small,
but equal quantities of H3O+
and OH− ions.
• molar concentrations are
indicated in brackets as
[H3O+] and [OH−].
[H3O+]
[OH−]
= 1.0 x 10−7 M
= 1.0 x 10−7 M
20
Ion Product of Water, Kw
The ion product constant, Kw, for water
• is the product of the concentrations of the hydronium
(H3O+ or H+ hydrogen ion) and hydroxide ions (OH-).
Kw
=
[ H3O+] [ OH− ]
• can be obtained from the concentrations in pure water.
Kw
=
[ H3O+] [ OH− ]
Kw
=
[1.0 x 10− 7 M] x [ 1.0 x 10− 7 M]
=
1.0 x 10− 14
21
Acidic Solutions
Adding an acid to pure water
• increases the [H3O+].
• cause the [H3O+] to exceed
1.0 x 10-7 M.
• decreases the [OH−].
22
Basic Solutions
Adding a base to pure water
• increases the [OH−].
• causes the [OH−] to exceed
1.0 x 10− 7M.
• decreases the [H3O+].
23
acidic – neutral – basic solutions
24
[H3
+
O]
determines acid or
neutral or base
1.0 x 10-7M = 0.0000001 = neutral
If < -7 (ie -1 through -6) = acidic
If > -7 (ie -8 through -14) = basic
25
Calculate [H3
Kw =
-14
1.0×10
O+]
or
+
=[H3O ]
[OH ]
x
[OH ]
If [H3O+ ] is known:
If [OH- ] is known:
26
27
Calculating [H3O+]
What is the [H3O+] of a solution if [OH−] is 5.0 x 10-8 M?
STEP 1: Write the Kw for water.
Kw =
[H3O+ ][OH− ] = 1.0 x 10−14
STEP 2: Rearrange the Kw expression.
14
1
.
0

10
[ H 3O  ] 
[OH- ]
STEP 3: Substitute [OH−].
14
1
.
0

10
-7 M
[ H 3O  ] 

2.0
×
10
5.0 10-8
28
Learning Check
If lemon juice has [H3O+] of 2 x 10−3 M, what is the [OH−] of the
solution?
Rearrange the Kw to solve for [OH- ]
Kw = [H3O+ ][OH− ] = 1.0 x 10−14
14
Kw
1.0 10
−12 M
[OH ] 


5
x
10
[H 3O  ]
2 10 3

29
Learning Check
The [OH−] of an ammonia solution is 4.0 x 10−2 M.
What is the [H3O+ ] of the solution?
14
1
.
0

10
[ H 3O  ] 
[OH- ]
14
1
.
0

10
[ H 3O  ] 

-2
4.0 10
2.5 x 10−13 M
30