ed. Brad Collins
Aqueous Chemistry
Chapter 5
Some images copyright © The McGraw-Hill Companies, Inc.
Sunday, August 18, 13
A solution is a homogenous mixture of 2 or more
substances at the molecular level
The solute(s) is(are) the substance(s) present in
the smaller amount(s)
The solvent is the substance present in the larger
amount
Solution
Solvent
Solute
Soft drink (l)
H2O
Sugar, CO2
Air (g)
N2
O2, Ar, CH4
Soft Solder (s)
Pb
Sn
5.1
Sunday, August 18, 13
Hydration is the process in which an ion is surrounded
by water molecules arranged in a specific manner.
δ−
δ+
H2
Ionic compounds dissolve by dissociation: The process of
breaking up into ions.
5.1
Sunday, August 18, 13
An electrolyte is a substance that, when dissolved in
water, results in a solution that can conduct electricity.
A nonelectrolyte is a substance that, when dissolved,
results in a solution that does not conduct electricity.
nonelectrolyt
weak
strong
5.1
Sunday, August 18, 13
Conduct electricity in solution?
Cations (+) and Anions (-)
Strong Electrolyte – 100% dissociation
NaCl (s)
H 2O
Na+ (aq) + Cl- (aq)
Weak Electrolyte – not completely dissociated
CH3COOH
CH3COO- (aq) + H+ (aq)
5.1
Sunday, August 18, 13
Ionization of acetic acid
CH3COOH
CH3COO- (aq) + H+ (aq)
A reversible reaction. The reaction can
occur in both directions.
Acetic acid is a weak electrolyte because its
ionization in water is incomplete.
5.1
Sunday, August 18, 13
A nonelectrolyte does not conduct electricity
because:
No cations (+) or anions (-) in solution
C6H12O6 (s)
H 2O
C6H12O6 (aq)
5.1
Sunday, August 18, 13
Solubility
• Solubility is the degree to which a compound dissolves in a
solvent.
• Several ways to categorize:
• Saturated, unsaturated, supersaturated
• Saturated: Solvent contains as much solute as it can hold
• Unsaturated: Solvent contains less solute than a saturated
solution
• Supersaturated: Solvent contains more solute than a
saturated solution.
5.2
Sunday, August 18, 13
Solubility Trends
• In order of priority:
• Group 1A compounds, ammonium salts, and all acids are soluble.
• Nitrates, acetates, chlorates, and perchlorates are soluble
• Silver, lead, mercury(I) and copper(I) compounds are insoluble
• Chlorides, bromides, and iodides are soluble
• Sulfates are soluble (except barium and calcium sulfate)
• Compounds with a –2 or –3 anion are insoluble
• Hydroxides are insoluble (except Group 1A, calcium and barium
hydroxides)
5.2
Sunday, August 18, 13
5.2
Sunday, August 18, 13
Practice: Solubility
• Classify the following compounds as soluble or insoluble, and cite the
solubility rule involved:
• Sodium chloride
• Silver nitrate
• Silver chloride
• Iron(II) chloride
• Magnesium sulfate
• Calcium sulfide
• Barium hydroxide
5.2
Sunday, August 18, 13
Precipitation Reactions
Precipitate – insoluble solid that separates from solution
precipitate
Pb(NO3)2 (aq) + 2NaI (aq)
PbI2 (s) + 2NaNO3 (aq)
molecular equation
Pb2+ + 2NO3- + 2Na+ + 2I-
PbI2 (s) + 2Na+ + 2NO3-
ionic equation
Pb2+ + 2IPbI2 (s)
PbI2 (s)
net ionic equation
Na+ and NO3- are spectator ions
5.2
Sunday, August 18, 13
Writing Net Ionic Equations
1. Write the balanced molecular equation.
2. Write the ionic equation showing the strong electrolytes
completely dissociated into cations and anions.
3. Cancel the spectator ions on both sides of the ionic equation
Write the net ionic equation for the reaction of silver
nitrate with sodium chloride.
AgNO3 (aq) + NaCl (aq)
AgCl (s) + NaNO3 (aq)
Ag+ + NO3- + Na+ + Cl-
AgCl (s) + Na+ + NO3-
Ag+ + Cl-
AgCl (s)
5.2
Sunday, August 18, 13
Practice: Writing Ionic
Equations
• Write the molecular and ionic equations
for the following chemical reaction:
– Aluminum nitrate + sodium hydroxide
5.2
Sunday, August 18, 13
Properties of Acids
Have a sour taste. Vinegar owes its taste to acetic acid. Citrus
fruits contain citric acid.
Cause color changes in plant dyes.
React with certain metals to produce hydrogen gas.
2HCl (aq) + Mg (s)
MgCl2 (aq) + H2 (g)
React with carbonates and bicarbonates to produce carbon
dioxide gas
2HCl (aq) + CaCO3 (s)
CaCl2 (aq) + CO2 (g) + H2O (l)
Aqueous acid solutions conduct electricity.
5.3
Sunday, August 18, 13
Arrhenius acid is a substance that produces H+ (H3O+) in water
Arrhenius base is a substance that produces OH- in water
5.3
Sunday, August 18, 13
Hydronium ion, hydrated proton, H3O+
5.3
Sunday, August 18, 13
Monoprotic acids
HCl
H+ + Cl-
HNO3
H+ + NO3-
CH3COOH
H+ + CH3COO-
Strong electrolyte, strong acid
Strong electrolyte, strong acid
Weak electrolyte, weak acid
Diprotic acids
H2SO4
H+ + HSO4-
Strong electrolyte, strong acid
HSO4-
H+ + SO42-
Weak electrolyte, weak acid
Triprotic acids
H3PO4
H2PO4HPO42-
H+ + H2PO4H+ + HPO42H+ + PO43-
Weak electrolyte, weak acid
Weak electrolyte, weak acid
Weak electrolyte, weak acid
5.3
Sunday, August 18, 13
Bases
Have a bitter taste.
Feel slippery. Many soaps contain bases.
Cause color changes in plant dyes.
Aqueous base solutions conduct electricity.
5.3
Sunday, August 18, 13
A Brønsted acid is a proton donor
A Brønsted base is a proton acceptor
base
acid
acid
base
A Brønsted acid must contain at least one
ionizable proton!
5.3
Sunday, August 18, 13
Identify each of the following species as a Brønsted acid,
base, or both. (a) HI, (b) CH3COO-, (c) H2PO4HI + H2O
H3O+ (aq) + I- (aq)
CH3COO- (aq) + H2O
Brønsted acid
CH3COOH + OH-
Brønsted base
H2PO4- (aq) + H2O
H3O+ (aq) + HPO42- (aq) Brønsted acid
H2PO4- (aq) + H2O
H3PO4 (aq) + OH–(aq) Brønsted base
5.3
Sunday, August 18, 13
Acid-Base (Neutralization) Reaction
acid + base
HCl (aq) + NaOH (aq)
H+ + Cl- + Na+ + OHH+ + OH-
salt + water
NaCl (aq) + H2O
Na+ + Cl- + H2O
H 2O
5.3
Sunday, August 18, 13
Gas-Forming Reactions
• Reactions that produce carbonic acid
• Carbonic acid decomposes in water to form more water and
carbon dioxide
• Reactions that produce sulfurous acid
• Aqueous sulfurous acid decomposes to form water and sulfur
dioxide gas
• Reactions that produce hydrogen sulfide, H2S(g)
• Reactions between metals and acids
• Metal + Acid
Salt + hydrogen gas
• Not all metals react with all acids to produce hydrogen gas
• Cu(s) + 4HNO3(aq)
Cu(NO3)2(aq) + 2NO2(g) + H2O(l)
5.4
Sunday, August 18, 13
Oxidation-Reduction Reactions
(electron transfer reactions)
2Mg (s) + O2 (g)
2Mg
O2 + 4e-
2Mg2+ + 4e- Oxidation half-reaction (lose e-)
2O2-
Reduction half-reaction (gain e-)
2Mg + O2 + 4e2Mg + O2
Sunday, August 18, 13
2MgO (s)
2Mg2+ + 2O2- + 4e2MgO
5.5
5.5
Sunday, August 18, 13
Oxidation number rules - Part 1
The charge the atom would have in a molecule (or an
ionic compound) if electrons were completely transferred.
1. Free elements (uncombined state) have an oxidation
number of zero.
Na, Be, K, Pb, H2, O2, P4 = 0
2. In monatomic ions, the oxidation number is equal to
the charge on the ion.
Li+, Li = +1; Fe3+, Fe = +3; O2-, O = -2
3. Group IA metals are +1, IIA metals are +2 and fluorine is
always –1.
4. The oxidation number of hydrogen is +1 except when it
is bonded to metals in binary compounds (e.g. LiH). In
these cases, its oxidation number is –1.
Sunday, August 18, 13
5.5
5. The oxidation number of oxygen is –2 except in H2O2
and O22- where it is –1.
6. Group 7A halogens (except fluorine) are -1 in binary
compounds. When bonded with oxygen, other halides
have + oxidation numbers
7. The sum of the oxidation numbers of all the atoms in
a molecule or ion is equal to the charge on the
molecule or ion.
HCO3Oxidation numbers of all
the elements in HCO3- ?
O = -2
H = +1
3x(-2) + 1 + ? = -1
C = +4
Sunday, August 18, 13
5.5
Figure 4.10 The oxidation numbers of elements in their compounds
5.5
Sunday, August 18, 13
Oxidation numbers of all
the elements in the
following ?
IF7
F = -1
7x(-1) + ? = 0
I = +7
NaIO3
Na = +1 O = -2
3x(-2) + 1 + ? = 0
I = +5
K2Cr2O7
O = -2
K = +1
7x(-2) + 2x(+1) + 2x(?) = 0
Cr = +6
5.5
Sunday, August 18, 13
Types of Oxidation-Reduction Reactions
Combination Reaction
A+B
0
0
S + O2
C
+4 -2
SO2
Decomposition Reaction
C
+1 +5 -2
2KClO3
A+B
+1 -1
0
2KCl + 3O2
5.5
Sunday, August 18, 13
Types of Oxidation-Reduction Reactions
Displacement Reaction
A + BC
0
+1
Sr + 2H2O
+4
0
TiCl4 + 2Mg
0
-1
Cl2 + 2KBr
AC + B
+2
0
Sr(OH)2 + H2 Hydrogen Displacement
0
+2
Ti + 2MgCl2 Metal Displacement
-1
0
2KCl + Br2
Halogen Displacement
5.5
Sunday, August 18, 13
The Activity Series for Metals
Hydrogen Displacement Reaction
M + BC
AC + B
M is metal
BC is acid or H2O
B is H2
Ca + 2H2O
Ca(OH)2 + H2
Pb + 2H2O
Pb(OH)2 + H2
Figure 4.15
5.5
Sunday, August 18, 13
Halogen Displacement
• The ability of one halogen to replace
another in a displacement reaction.
• Order: F2 > Cl2 > Br2 > I2
– Example:
• Cl2 (g) + 2 KBr (aq)
• Cl2 (g) + 2 NaI (aq)
• Br2 (g) + 2 KI (aq)
2KCl (aq) + Br2 (l)
2NaCl (aq) + I2 (s)
2KBr (aq) + I2 (s)
5.5
Sunday, August 18, 13
Types of Oxidation-Reduction Reactions
Disproportionation Reaction
Element is simultaneously oxidized and reduced.
0
Cl2 + 2OH-
+1
-1
ClO- + Cl- + H2O
Chlorine Chemistry
5.5
Sunday, August 18, 13
Classify the following reactions.
Ca2+ + CO32NH3 + H+
Zn + 2HCl
Ca + F2
CaCO3
NH4+
ZnCl2 + H2
CaF2
Precipitation
Acid-Base
Redox (H2 Displacement)
Redox (Combination)
4.4
Sunday, August 18, 13
Zn (s) + CuSO4 (aq)
Zn
Zn2+ + 2e- Zn is oxidized
Cu2+ + 2e-
ZnSO4 (aq) + Cu (s)
Zn is the reducing agent
Cu Cu2+ is reduced Cu2+ is the oxidizing agent
Copper wire reacts with silver nitrate to form silver metal.
What is the oxidizing agent in the reaction?
Cu (s) + 2AgNO3 (aq)
Cu
Ag+ + 1e-
Cu(NO3)2 (aq) + 2Ag (s)
Cu2+ + 2eAg Ag+ is reduced Ag+ is the oxidizing agent
4.4
Sunday, August 18, 13
Chemistry in Action: Breath Analyzer
+6
3CH3CH2OH + 2K2Cr2O7 + 8H2SO4
+3
3CH3COOH + 2Cr2(SO4)3 + 2K2SO4 + 11H2O
4.4
Sunday, August 18, 13
Molarity
The concentration of a solution is the amount of solute
present in a given quantity of solvent or solution.
M = molarity =
moles of solute
liters of solution
What mass of KI is required to make 500. mL of
a 2.80 M KI solution?
volume KI
500. mL x
M KI
1L
1000 mL
moles KI
x
2.80 mol KI
1 L soln
M KI
x
166 g KI
1 mol KI
grams KI
= 232 g KI
5.6
Sunday, August 18, 13
5.6
Sunday, August 18, 13
Practice: Solution
Concentration
• What is the molarity of an 85.0-mL
ethanol (C2H5OH) solution, which
contains 1.77g of ethanol?
5.6
Sunday, August 18, 13
Titrations
In a titration a solution of accurately known concentration
(titrant) is added gradually added to another solution of
unknown concentration (titrand) until the chemical reaction
between the two solutions is complete.
Equivalence point – the point at which the reaction is complete
moles titrant (VA*MA) = moles titrand (VB*MB)
Indicator – substance that changes color at (or near) the
equivalence point
Example:
Slowly add
base
to unknown acid
UNTIL
the indicator
changes color
5.6
Sunday, August 18, 13
What volume of a 1.420 M NaOH solution is
Required to titrate 25.00 mL of a 4.50 M H2SO4
solution?
WRITE THE CHEMICAL EQUATION!
H2SO4 + 2NaOH
volume acid
M
moles acid
acid
25.00 mL x
4.50 mol H2SO4
1000 mL soln
rx
2H2O + Na2SO4
moles base
coef.
x
2 mol NaOH
1 mol H2SO4
x
M
bas
volume base
1000 ml soln
1.420 mol NaOH
= 158 mL
5.6
Sunday, August 18, 13
Dilution is the procedure for preparing a less concentrated
solution from a more concentrated solution.
Dilution
Add Solvent
Sunday, August 18, 13
Moles of solute
before dilution (i)
=
Moles of solute
after dilution (f)
MiVi
=
MfVf
5.6
How would you prepare 60.0 mL of 0.2 M
HNO3 from a stock solution of 4.00 M HNO3?
MiVi = MfVf
Mi = 4.00
Vi =
Mf = 0.200
Vf = 0.06 L
Vi = ? L
MfVf
0.200 x 0.06
=
= 0.003 L = 3 mL
4.00
Mi
3 mL of acid + 57 mL of water = 60 mL of solution
5.6
Sunday, August 18, 13