Transcript No Slide Title

Chapter 4 (semester 2/2010)
Reactions in Aqueous Solution
prepared by A. Kyi Kyi Tin
Ref: Raymong Chang. Chemistry Ninth Edition, McGraw – Hill
International Edition
4.1 General Properties of Aqueous Solutions
4.2 Precipitation Reactions
4.3 Acid- Base Reactions
4.4 Oxidation – Reduction Reactions
4.5 Concentration of Solutions
4.1 General Properties of Aqueous Solutions
Solution = [ solute
+
[smaller amount
[CLEAR,
solvent]
+
larger amount]
HOMOGENEOUS MIXTURE]
Aqueous solution = solute (liquid “or” solid) + solvent (water)
Solution
Solvent
Solute
Sea water
H2O
Salt (NaCl)
Air (g)
N2
O2, Ar, CH4
Alloy
Cu
Ni
4.1
Two types of Solutes
Electrolyte
Non-electrolyte
When dissolved in water
can conduct electricity
When dissolved in water
does not conduct electricity
nonelectrolyte
weak electrolyte
Incomplete
dissociation/reversible
strong electrolyte
100%dissociation/
reversible reaction
Ref: Raymond Chang Chemistry, Ninth Edition
Figure 4.1, Page 120
4.2
Conduct electricity in solution?
Dissociation means breaking up into..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)
Note: Pure water contains very few ions, cannot
conduct electricity (extremely weak electrolyte)
4.3
Hydration: is the process in which an ion is surrounded
by water molecules arranged in a specific manner.
Water, electrically neutral molecule has a positive poles
and negative poles, it is a polar solvent.
Ex: when NaCl dissolves in water Na+ ions and Clions are separated from each other and undergo
“hydration”.
Hydration helps to stabilize ions in solution and
prevents cations from combining with anions.
4.4
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.
4.5
Nonelectrolyte does not conduct electricity?
No cations (+) and anions (-) in solution
C6H12O6 (s)
H 2O
C6H12O6 (aq)
4.6
4.2 Precipitation Reactions
(Metathesis reaction) or (Double Displacement reaction)
One product is insoluble solid
precipitate
Pb(NO3)2 (aq) + 2NaI (aq)
PbI2 (s) + 2NaNO3 (aq)
molecular equation
Pb2+ + 2NO3- + 2Na+ + 2I-
PbI2 (s) + 2Na+ + 2NO3-
ionic equation
Pb2+ + 2I-
PbI2 (s)
net ionic equation
Na+ and NO3- are spectator ions
4.7
Solubility: Maximum amount of solute that will dissolve in
a given quantity of solvent in a specific temperature.
soluble
Substances:
Slightly soluble
insoluble
Soluble : fair amount is visibly dissolves when added to water
-All ionic compounds are strong electrolytes, but they are not
equally soluble.
-Even insoluble compounds dissolve to a certain extent
Examples are: (NH4)2CO3, (NH4)3PO4,(NH4)2S,(NH4)2CrO4
4.8
4.3 Acid-Base Reactions
ACID: Arrhenius acid is a substance that produces H+ (H3O+) in water
BASE: Arrhenius base is a substance that produces OH- in water
4.9
Hydronium ion, hydrated proton, H3O+
4.10
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!
4.11
Monoprotic acids
HCl
H+ + Cl-
HNO3
H+ + NO3H+ + CH3COO-
CH3COOH
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
4.12
Practice question: Identify each of the following species as a
Brønsted acid, base, or both. (a) HI, (b) CH3COO-, (c) H2PO4HI (aq)
H+ (aq) + Br- (aq)
CH3COO- (aq) + H+ (aq)
H2PO4- (aq)
Brønsted acid
CH3COOH (aq)
H+ (aq) + HPO42- (aq)
H2PO4- (aq) + H+ (aq)
H3PO4 (aq)
Brønsted base
Brønsted acid
Brønsted base
4.13
Neutralization Reaction
acid + base
HCl (aq) + NaOH (aq)
H+ + Cl- + Na+ + OH-
H+ + OH-
salt + water
NaCl (aq) + H2O
Na+ + Cl- + H2O
H2O
4.14
4.4 Oxidation-Reduction Reactions
REDOX REACTIONS(electron transfer reactions)
2Mg (s) + O2 (g)
2Mg
O2 + 4e-
2Mg +
Oxidized
Reducing Agent
(donates electrons
to oxygen and
causes oxygen to
be reduced)
2Mg2+ + 4e2O2-
O2
Reduced
Oxidizing Agent
(accepts electrons
from Magnesium
and causes
Magnesium to be
oxidized)
2MgO (s)
Oxidation half-reaction (loss of e-)
Reduction half-reaction (gain e-)
2MgO
OIL RIG
Oxidation Is Loss
Reduction Is Gain
4.15
Zn (s) + CuSO4 (aq)
Zn
ZnSO4 (aq) + Cu (s)
Zn2+ + 2e- Zn is oxidized
Cu2+ + 2e-
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
4.16
IF7
Oxidation numbers of all
the elements in the
following ?
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
4.17
Types of Redox Reactions
(i)
Combination Reaction
Two or more substances combine to form a single product.
0
0
S(s) + O2 (g)
+4 -2
SO2(g)
(ii) Decomposition Reaction
Breakdown of a compound into two or more components.
+2 -2
2 HgO(s)
0
2Hg(l)
0
+ O2(g)
4.18
(iii) Displacement Reaction
Halogen displacement
According to Activity Series
F2 > Cl2 > Br2 > I2
i.e Molecular fluorine can replace chloride, bromide and
iodide ions in solution. On the other hand, Molecular chlorine
can replace bromide and iodide ions in solution
0
-1
-1
Cl2 (g) + 2 KBr(aq)
0
0
2KCl(aq) + Br2(l)
-1
Cl2 (g) + 2 NaI(aq)
-1
0
2NaCl(aq) + I2(l)
4.19
Classify the following reactions.
Ca2+ + CO32NH3 + H+
Zn + 2HCl
Ca + F2
CaCO3
NH4+
ZnCl2 + H2
CaF2
Precipitation
Acid-Base
Redox (H2 Displacement)
Redox (Combination)
4.20
4.5 Concentration of Solutions
concentration : amount of solute present in a given
quantity of solvent or solution.
Most commonly used unit is “Molarity”
M = molarity =
moles of solute
liters of solution
n
M 
V
4.21
Dilution is the procedure for preparing a less concentrated
solution from a more concentrated solution.
Dilution
Add Solvent
Moles of solute
before dilution (i)
=
Moles of solute
after dilution (f)
MiVi
=
MfVf
4.22
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
MfVf
Mi
Vf = 0.06 L
Vi = ? L
0.200 x 0.06
=
= 0.003 L = 3 mL
4.00
3 mL of acid + 57 mL of water = 60 mL of solution
Ref: power point presentation for instructors
(Mc- Graw hill series,www.mhhe.com/chemistry)
4.23