Transcript Acids, Bases and Salts Chapter 15 Hein and Arena Version 1.1 Eugene Passer Chemistry Department 1 College Bronx Community © John Wiley and Sons, Inc.

Acids, Bases and Salts
Chapter 15
Hein and Arena
Version 1.1
Eugene Passer
Chemistry Department
1 College
Bronx Community
© John Wiley and Sons, Inc.
Chapter Outline
15.1 Acids and Bases
15.8 Ionization of Water
15.2 Reactions of Acids
15.9 Introduction to pH
15.3 Reactions of Bases
15.10 Neutralization
15.4 Salts
15.5 Electrolytes and
Nonelectrolytes
15.6 Dissociation and Ionization
of Electrolytes
15.7 Strong and Weak
Electrolytes
15.11 Writing Net Ionic
Equations
15.12 Acid Rain
15.13 Colloids: an Introduction
15.14 Properties of Colloids
2
Acids and Bases
3
Acid Properties
• sour taste
• change the color of litmus from blue to
red.
These properties are due to the release
of hydrogen ions, H+, into water solution.
• react with
– metals such as zinc and magnesium to
produce hydrogen gas
– hydroxide bases to produce water and an
ionic compound (salt)
– carbonates to produce carbon dioxide.
4
Base Properties
•
•
•
•
bitter or caustic taste
a slippery, soapy feeling.
the ability to change litmus red to blue
the ability to interact with acids
5
• Svante Arrhenius was a Swedish
scientist who lived from 1859-1927.
• In 1884 he advanced a theory of acids
and bases.
6
An Arrhenius acid “is a hydrogencontaining substance that dissociates to
produce hydrogen ions.”
HA → H+ + Aacid
7
An Arrhenius base is a hydroxidecontaining substance that dissociates
to produce hydroxide ions in aqueous
solution.
MOH → M+(aq) + OH-(aq)
base
8
An Arrhenius acid solution contains an excess of H+ ions.
An Arrhenius base solution contains an excess of OH- ions.
9
• J.N. Bronsted (1897-1947) was a
Danish chemist and T. M. Lowry
(1847-1936) was an English chemist.
• In 1923 they advanced their theory of
acids and bases.
10
A Bronsted-Lowry acid is a proton (H+) donor.
A Bronsted-Lowry base is a proton (H+) acceptor.
11
proton acceptor
Bronsted-Lowry
Acid
Bronsted-Lowry
Base
proton
donor
HCl + H2O(l) → H3O+(aq) + Cl-(aq)
12
ionion ishydrogen ion
ahydrogen
hydronium
does formed
not existcombines with water
in water
13
Conjugate acid-base pairs differ by a proton.
When an acid donates a proton it becomes the conjugate
base.
HCl(g) → Cl-(aq)
acid
base
14
Conjugate acid-base pairs differ by a proton.
When a base accepts a proton it becomes the conjugate acid.
H2O (l) → H3O+(aq)
base
acid
15
Conjugate acid-base pairs differ by a proton.
HCl(g) + H2O (l) → Cl-(aq) + H3O+(aq)
acid
base
base
acid
16
Conjugate acid-base pairs differ by a proton.
HCl(g) + H2O (l) → Cl-(aq) + H3O+(aq)
acid
base
base
acid
17
• In 1923 G. N. Lewis developed a more
comprehensive theory of acids and
bases.
• The Lewis theory deals with the way in
which a substance with an unshared
pair of electrons reacts in an acid-base
type of reaction.
18
A Lewis acid is an electron-pair acceptor.
A Lewis base is an electron-pair donor.
19
Electron
Pair
Lewis Acid
Acceptor
Electron pair
donated to H+
Lewis
Base
Electron
Pair Donor
20
Electron
Pair
Lewis Acid
Acceptor
Electron pair
donated to B
Lewis
Base
Electron
Pair Donor
21
22
Reactions of Acids
23
In aqueous solution, the H+ or H3O+ ions are
responsible for the characteristic reactions of
acids.
24
Reaction with Metals Acids react with metals
that lie above hydrogen in the activity series of
element to produce hydrogen and an ionic
compound (salt):
acid + metal → hydrogen + ionic compound
2HCl(aq) + Ca(s) → H2(g) + CaCl2(aq)
H2SO4(aq) + Mg(s) → H2(g) + MgSO4(aq)
25
Reaction with Metals Oxidizing acids react
with metals to produce water instead of
hydrogen:
3Zn(s) + 8HNO3(dilute) → 3Zn(NO3)2 (aq) + 2NO(g) + 4H2O(l)
26
Reaction with Bases The reaction of an acid
with a base is called a neutralization reaction.
In an aqueous solution the products are a salt
and water:
HBr(aq) + KOH(aq) → KBr(aq) + H2O(l)
acid
base
salt
2HNO3(aq) + Ca(OH)2(aq) → Ca(NO3)2(aq) + 2H2O(l)
acid
base
salt
27
In an aqueous
solution the products are a salt and water. This
type of reaction is closely related to that of an
acid with a base:
Reaction with Metal Oxides
2HCl(aq) + Na2O(s) → 2NaCl(aq) + H2O(l)
acid
metal oxide
salt
H2SO4(aq) + MgO(s) → MgSO4(aq) + H2O(l)
acid
metal oxide
salt
28
Most acids react
with carbonates to produce carbon dioxide,
water and an ionic compound:
Reaction with Carbonates
2HCl(aq) + Na2CO3(aq) → 2NaCl(aq) + H2O(l) + CO2(g)
acid
carbonate
salt
H2SO4(aq) + MgCO3(s) → MgSO4(aq) + H2O(l) + CO2(g)
acid
carbonate
salt
HCl(aq) + NaHCO3(aq) → NaCl(aq) + H2O(l) + CO2(g)
acid
carbonate
salt
29
Carbonic acid (H2CO3) is not the product when an
acid reacts with a carbonate because carbonate
spontaneously decomposes into carbon dioxide and
water.
H2CO3(aq) → CO2(g) + H2O(l)
30
Reactions of Bases
31
Reaction with Acids The reaction of an acid
with a base is called a neutralization reaction.
In an aqueous solution the products are a salt
and water:
HBr(aq) + KOH(aq) → KBr(aq) + H2O(l)
acid
base
salt
2HNO3(aq) + Ca(OH)2(aq) → Ca(NO3)2(aq) + 2H2O(l)
acid
base
salt
32
Hydroxides of
certain metals are amphoteric, meaning they
are capable of reacting as either an acid or a
base:
Amphoteric
Hydroxides
Zn(OH)2 + 2HCl(aq) → ZnCl2(aq) + 2H2O(l)
base
acid
salt
Zn(OH)2 + 2KOH(aq) → K2Zn(OH)4(aq)
Lewis acid
base
33
Reaction of NaOH and KOH with Certain
Metals Some amphoteric metals react directly
with the strong bases sodium hydroxide and
potassium hydroxide to produce hydrogen:
base + metal + water → salt + hydrogen
2KOH(aq) + 2Al(s) + 6H2O(l) → 2KAl(OH)4(aq) + 3H2(g)
Lewis acid
2NaOH(aq) + Zn(s) + 2H2O(l) → Na2Zn(OH)4(aq) + H2(g)
Lewis acid
34
Salts
35
Salts can be considered compounds
derived from acids and bases. They consist
of positive metal or ammonium ions
combined with nonmetal ions (OH- and
O2- excluded).
Salts are usually
Chemists
use thecrystalline
terms ionic
and compound
have high
and saltand
melting
interchangeably.
boiling points.
36
Salt Formation
The negative
positive ion
ion of
the salt is derived
from the acid.
base.
base NaOH
HCl acid
NaCl
salt
37
Electrolytes and
Nonelectrolytes
38
Nonelectrolytes
Electrolytes are
aresubstances
substanceswhose
whose
aqueous
aqueous
solutions
solutions
do conduct
not conduct
electricity.
electricity.
Nonelectrolytes
Electrolytes areare
capable
not capable
of producing
of producing
ions
ions
in solution.
in solution.
39
Classes of compounds that are
electrolytes are:
– acids
– bases
– salts
– solutions of oxides that form an acid or a
base
40
41
Dissociation and
Ionization of Electrolytes
42
Dissociation is the process by which the ions
of a salt separate as the salt dissolves.
43
In a crystal of sodium chloride positive
sodium ions are bonded to negative chloride
ions.
44
15.2
In aqueous solution the sodium and chloride
ions dissociate from each other.
45
15.2
In aqueous solution the sodium and chloride
ions dissociate from each other.
46
15.2
Na+ and Cl- ions hydrate with H2O molecules.
47
15.2
The equation representing the dissociation of
NaCl is:
NaCl(s) + (x+y)H2O → Na+(H2O)x + Cl-(H2O)y
The equation can be written more simply as:
NaCl(s) → Na+(aq) + Cl-(aq)
48
the formation
of ions.
Ionization is
occurs
as the result
of a chemical
reaction of certain substances with water.
49
Acetic acid ionizes in water to form acetate
ion and hydronium ion.
HC2H3O2 + H2O → H3O+ + C2H3O2-
→
Lewis acid
Lewis base Lewis acid
Lewis base
The equation can be written more simply as:
HC3H3O2 → H+ + C2H3O2-
→
In the absence of water ionization reactions do not
occur.
50
Strong and
Weak Electrolytes
51
Strong Electrolyte An electrolyte that is
Weak Electrolyte An electrolyte that is
essentially 100% ionized in aqueous
ionized to a small extent in aqueous solution.
solution.
52
• Most salts are strong electrolytes
• Strong acids and bases (highly ionized)
are strong electrolytes.
• Weak acids and bases (slightly ionized)
are weak electrolytes.
53
100%
HCl
Strong Acid
Solution
ionized
HC2H3O2
1%
Weak
ionized
Acid
Solution
54
15.3
Both the ionized and unionized forms of a weak
electrolyte are present in aqueous solution.
+
→
HC2H3O2(aq)
H (aq) + C
C22H3O2(aq)
(aq )
→
unionized
ionized
55
HNO3, a strong acid, is 100 % dissociated.
+
HNO3(aq) → H (aq) + NO3(aq)
(aq )
HNO2, a weak acid, is only slightly ionized.
HNO2(aq) → H+(aq) + NO2- (aq)
(aq )
→
56
57
Electrolytes yield two or more ions per formula
unit upon dissociation.
NaOH → Na+(aq) + OH-(aq)
two ions in solution per
formula unit
Na2SO4 →
2Na+(aq) +
2-SO44 (aq)
SO (aq)
three ions in solution
per formula unit
Fe2(SO4 )3 →
2Fe3+(aq) +
five ions in solution per
formula unit
2-3SO4 (aq)
3SO (aq )
58
Electrolytes yield two or more moles of ions per
mole of electrolyte upon dissociation.
NaOH → Na+(aq) + OH-(aq)
1 mole
Na2SO4 →
1 mole
Fe2(SO4 )3 →
1 mole
1 mole
1 mole
2Na+(aq) +
2 moles
2-SO44 (aq)
SO (aq)
2Fe3+(aq) +
2 moles
1 mole
2-3SO4 (aq)
3SO (aq )
3 moles
59
Colligative Properties of
Electrolyte Solutions
60
Substances that form ions in aqueous solutions change
the colligative properties of water in proportion to the
number of ions formed.
NaOH → Na+(aq) + OH-(aq)
1 mole
1 mole
1 mole
Two moles of ions will depress the freezing point of
water twice that of one mole of a nonelectrolyte.
Fe2(SO4 )3 →
1 mole
2Fe3+(aq) +
2 moles
2-3SO4 (aq)
3SO (aq )
3 moles
Five moles of ions will depress the freezing point of
water five times that of one mole of a nonelectrolyte.
61
Ionization of Water
62
hydroxide
ion
Water ionizes slightly.
hydronium ion
H2O + H2O →
→ H3O+ + OHbase
→
acid
acid
base
Water ionization can be expressed more simply as:
→ H+ + OHH2O →
→
[H3O+] or [H+] = 1.0 x 10-7 mol/L
[OH-] = 1.0 x 10-7 mol/L
63
Two out of every 1 billion water molecules are ionized
.
Introduction to pH
64
pH is the negative logarithm of the hydrogen
ion concentration.
pH = -log[H+]
65
Calculation of pH
66
pH = -log[H+]
[H+] = 1 x 10-5
when this number
is exactly 1
pH = this number
without
pHthe
= 5minus
sign.
67
pH = -log[H+]
[H+] = 2 x 10-5
when this number is
one significant figure
between 1 and 10
pH is between this
number and the
ph = 4.7
next lower number
one decimal
place
(between
4 and
5).
The number of decimal places of a logarithm is
equal to the number of significant figures in the
68
original number.
What is the pH of a solution with an [H+] of 1.0 x 10-11?
2 significant figures
pH = - log(1.0 x 10-11)
pH = 11.00
2 decimal places
69
What is the pH of a solution with an [H+] of 6.0 x 10-4?
2 significant figures
log[H+] = log 6.0 x 10-4 = -3.22
pH = - log[H+] = -(3.22) = 3.22
2 decimal places
70
What is the pH of a solution with an [H+] of 5.47 x 10-8?
3 significant figures
log[H+] = log 5.47 x 10-8 = -7.262
pH = - log[H+] = -(7.262) = 7.262
3 decimal places
71
The pH scale of Acidity and Basicity
72
15.4
Neutralization
73
Neutralization The reaction of an acid and a
base to form a salt and water.
HCl(aq) + KOH(aq) → KCl(aq) + H2O(l)
acid
base
salt
74
Titrations
75
Titration The process of measuring the
volume of one reagent required to react with
a measured mass or volume of another
reagent.
76
42.00 mL of 0.150 M NaOH solution is required to
neutralize 50.00 mL of hydrochloric acid solution.
What is the molarity of the acid solution.
The equation for the reaction is
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
acid
base
salt
Calculate the liters of NaOH that react.
mol
Molarity =
L
1L 

= 0.04200
 42.00 mLThe

unit of volume
when L


Convert
mL
of NaOH to
1000
mL

using molarity is liters.
liters of NaOH
Calculate the moles of NaOH that react.
0.150 mol NaOH 

 0.004200 L  
 = 0.00630 mol NaOH
77
1L


42.00 mL of 0.150 M NaOH solution is required to
neutralize 50.00 mL of hydrochloric acid solution.
What is the molarity of the acid solution.
The equation for the reaction is
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
acid
base
salt
The moles
mole ratio
of NaOH
of HClthat
to NaOH
react equals
is 1:1 the moles of
HCl that react.
0.00630 mol NaOH react. 0.00630 mol HCl react.
The molarity of the HCl solution is
mol 0.0630 mol HCl
M=
=
 0.126 M HCl 78
L
0.05000 L
Writing Net Ionic Equations
79
In the un-ionized equation all compounds
are written using their molecular or formula
expressions.
HCl(aq) + KOH(aq) → KCl(aq) + H2O(l)
acid
base
salt
In the total ionic equation all ions present in
solution are written.
(H+ + Cl-) + (K+ + OH-) → K+ + Cl- + H2O
that do
not participate
inthe
a chemical
In the netIons
ionic
equation
only
ions
that react
+
Cl
ion
does
K
ion
not
does
react.
not
react.
reaction are called spectator ions.
are written.
H+(aq) + OH-(aq) → H2O(l)
80
Rules for Writing Equations
1. Strong electrolytes in solution are
written in their ionic form.
2. Weak electrolytes are written in their
molecular (un-ionized) form.
3. Nonelectrolytes are written in their
molecular form.
81
4. Insoluble substances, precipitates and
gases are written in their molecular
forms.
5. The net ionic equation should include
only substances that have undergone
a chemical change. Spectator ions
are omitted from the net ionic
equation.
6. Equations must be balanced both in
atoms and in electrical charge.
82
Examples
83
2AgNO3(aq) + BaCl2(aq) → 2AgCl(s) + Ba(NO3)2(aq)
un-ionized equation
spectator ions
(2Ag+ + 2NO3- ) + (Ba2+ + 2Cl-) → 2AgCl(s) + (Ba2+ + 2NO3- )
total ionic equation
precipitate
Ag+ + Cl- → AgCl(s)
net ionic equation
84
Na2CO3 (aq ) + H2SO4 (aq )  Na 2SO4 + H2O(l ) + CO2 (g )
un-ionized equation
spectator ions
 2Na + CO  +  2H
+
23
+
+ SO24  
 2Na
+
+ SO24  + H2O(l ) + CO2 (g )
total ionic equation
gas
CO32- + 2H+  H2O(l ) + CO2 (g )
net ionic equation
85
Mg(s) + 2HCl(aq) → MgCl2(aq) + H2(g)
un-ionized equation
spectator ion
Mg(s) + (2H+ + 2Cl-) → (Mg2+ + 2Cl-)+ H2(g)
total ionic equation
Electrical charge on both sides of the equation = +2
Mg + 2H+ → Mg2+ + H2(g)
net ionic equation
86
Acid Rain
87
Acid rain any atmospheric precipitation that
is more acidic than usual.
88
• pH of rain is lower in the eastern US
and higher in the western US.
• Unpolluted rain has a pH of 5.6
because of carbonic acid formation in
the atmosphere.
CO2(g) + H2O(l) → H2CO3(aq) → H+ + HCO3
→
89
→
• pH of rain is lower in the eastern US
and higher in the western US.
• Unpolluted rain has a pH of 5.6
because of carbonic acid formation in
the atmosphere.
CO2 (g ) + H2O(l )
H2CO3 (aq)
2H3O+(aq) + CO32- (aq)
90
Process of Acid Rain Formation
1. emission of nitrogen and sulfur oxides
into the air
2. transportation
of these
oxides
into the
From the burning
of fossil
fuels.
atmosphere
3. chemical reactions between the
oxides and water forming sulfuric
acid (H2SO4) and nitric acid (HNO3)
4. rain or snow, which carries the acids
to the ground
91
Effects of Acid Rain
1. freshwater plants and animals decline
significantly when rain is acidic
2. aluminum is leached from the soil
into lakes and adversely affects fish
gills.
3. the waxy protective coat on plants is
dissolved making them vulnerable to
bacteria and fungal attack
92
Effects of Acid Rain
4. it is responsible for extensive and
continuing damage to buildings,
monuments and statues
5. it reduces the durability of paint and
promotes the deterioration of paper,
leather and cloth
93
Colloids: An Introduction
94
Colloid A dispersion in which the dispersed
particles are larger than the solute ions or
molecules of a true solution and smaller than
the particles of a mechanical suspension.
95
• Colloid is derived from the Greek word
“kolla” meaning “glue.”
• The term colloid does not imply a
system has a gluelike quality.
97
• The fundamental difference between
the particles of a colloidal dispersion
and a colloid is the size of the particles.
• In ordinary solutions the size of solute
particles range from 0.1 to 1 nm.
• The size of colloidal particles range
from 1 to 1,000 nm.
• In a solution the particles are usually
single ions or molecules.
• In a colloid the particles are usually
aggregations of ions or molecules.
98
99
Properties of Colloids
100
• In 1827 Robert Brown illuminated an
aqueous suspension of pollen under a
high powered microscope.
• He observed a trembling erratic motion
of the pollen grains.
• This erratic motion is characteristic of
colloids in general.
• This random motion is called
Brownian movement.
101
• When an intense beam of light is
passed through an ordinary solution
and viewed at an angle, the beam
passing through the solution is hardly
The visible.
Tyndall effect occurs because colloidal
• A beam
of light
is clearly
visible
and
particles
are large
enough
to scatter
light.
sharply outlined when it is passed
through a colloidal dispersion.
• This phenomenon is known as the
Tyndall effect.
102
• Colloidal particles have huge surface
areas in comparison to the volume of the
same particles if they were aggregated
into one large particle.
• Colloidal particles become electrically
charged when they adsorb ions on their
surfaces.
• This occurs because surface atoms or
ions of the colloid attract and adsorb
ions or polar molecules from the
dispersion medium.
103
Key Concepts
15.1 Acids and Bases
15.8 Ionization of Water
15.2 Reactions of Acids
15.9 Introduction to pH
15.3 Reactions of Bases
15.10 Neutralization
15.4 Salts
15.5 Electrolytes and
Nonelectrolytes
15.6 Dissociation and Ionization
of Electrolytes
15.7 Strong and Weak
Electrolytes
15.11 Writing Net Ionic
Equations
15.12 Acid Rain
15.13 Colloids: an Introduction
15.14 Properties of Colloids104