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Reactions in Aqueous Solutionprepared by A. Kyi Kyi Tin
Ref: Raymong Chang. Chemistry Twelfth Edition, McGraw – Hill International Edition
4.1 General Properties of Aqueous Solutions4.2 Precipitation Reactions4.3 Acid- Base Reactions4.4 Oxidation – Reduction Reactions4.5 Concentration of Solutions
Chapter 4 (semester 1/2016)
4.1
4.1 General Properties of Aqueous SolutionsSolution = [ solute + solvent]
[smaller amount + larger amount]
[CLEAR, HOMOGENEOUS MIXTURE]
Aqueous solution = solute (liquid “or” solid (gas)) + solvent (water)
Solution Solvent Solute
Sea water
Air (g)
Alloy
H2O
N2
Cu
Salt (NaCl)
O2, Ar, CH4
Ni
Two types of Solutes
nonelectrolyte weak electrolyte strong electrolyte
4.2
Non-electrolyte
When dissolved in water does not conduct electricity
Electrolyte
When dissolved in water can conduct electricity
Incomplete dissociation/reversible
100%dissociation/One-sided reaction
Ref: Raymond Chang Chemistry, Eleventh Edition
Strong Electrolyte – 100% dissociation
NaCl (s) Na+ (aq) + Cl- (aq)H2O
Weak Electrolyte – not completely dissociated
CH3COOH CH3COO- (aq) + H+ (aq)
Conduct electricity in solution?
Dissociation means breaking up into..Cations (+) and Anions (-)
4.3
Note: Pure water contains very few ions, can conduct electricity slightly (extremely weak
electrolyte)
Hydration: is the process in which an ion is surroundedby water molecules arranged in a specific manner.
Water, electrically neutral molecule has a positive polesand negative poles, ∴it is a polar solvent.
Ex: when NaCl dissolves in water Na+ ions and Cl-ions are separated from each other and undergo
“hydration”.
Hydration helps to stabilize ions in solution and prevents cations from combining with anions.
4.4
6
Hydration is the process in which an ion is surrounded by water molecules arranged in a specific manner.
δ+
δ−
H2O
Ionization of acetic acid
CH3COOH CH3COO- (aq) + H+ (aq)
4.5
A reversible reaction. The reaction can occur in both directions.
Acetic acid is a weak electrolyte because its ionization in water is incomplete.
Nonelectrolyte does not conduct electricity?
No cations (+) and anions (-) in solution
4.6
C6H12O6 (s) C6H12O6 (aq)H2O
Ref: Raymond Chang Chemistry, Ninth Edition
Page 121
4.2 Precipitation Reactions (Metathesis reaction) or (Double Displacement reaction)
One product is insoluble solid
molecular equation
ionic equation
net ionic equation
Pb2+ + 2NO3- + 2Na+ + 2I- PbI2 (s) + 2Na+ + 2NO3
-
Na+ and NO3- are spectator ions
Pb(NO3)2 (aq) + 2NaI (aq) PbI2 (s) + 2NaNO3 (aq)
precipitate
Pb2+ + 2I- PbI2 (s)
4.7
4.8
Solubility: Maximum amount of solute that will dissolve in a given quantity of solvent in a specific temperature.
Substances:
soluble
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
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
4.3 Acid-Base Reactions
Ref: Raymond Chang Chemistry, Ninth EditionFigure 4.7,4.8 Page 128,129
Electrostatic potential map of the Hydronium ion, hydrated proton, H3O+
4.10
Ref: Raymond Chang Chemistry, Eleventh Edition
the most electron- rich
region
the most electron-poor
region
A Brønsted acid is a proton donorA Brønsted base is a proton acceptor
acidbase acid base
4.11
A Brønsted acid must contain at least one ionizable proton!
Ref: Raymond Chang Chemistry, Ninth Edition
Figure 4.8, Page 129
Monoprotic acidsHCl H+ + Cl-
HNO3 H+ + NO3-
CH3COOH H+ + CH3COO-
Strong electrolyte, strong acid
Strong electrolyte, strong acid
Weak electrolyte, weak acid
Diprotic acidsH2SO4 H+ + HSO4
-
HSO4- H+ + SO4
2-
Strong electrolyte, strong acid
Weak electrolyte, weak acid
Triprotic acidsH3PO4 H+ + H2PO4
-
H2PO4- H+ + HPO4
2-
HPO42- H+ + PO4
3-
Weak electrolyte, weak acidWeak electrolyte, weak acidWeak 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) H2PO4
-
HI (aq) H+ (aq) + Br- (aq) Brønsted acid
CH3COO- (aq) + H+ (aq) CH3COOH (aq) Brønsted base
H2PO4- (aq) H+ (aq) + HPO4
2- (aq)
H2PO4- (aq) + H+ (aq) H3PO4 (aq)
Brønsted acid
Brønsted base
4.13
Neutralization Reaction
acid + base salt + water
HCl (aq) + NaOH (aq) NaCl (aq) + H2O
H+ + Cl- + Na+ + OH- Na+ + Cl- + H2O
H+ + OH- H2O
4.14
4.4 Oxidation-Reduction ReactionsREDOX REACTIONS(electron transfer reactions)
2Mg (s) + O2 (g) 2MgO (s)
2Mg 2Mg2+ + 4e-
O2 + 4e- 2O2-
Oxidation half-reaction (loss of e-)
Reduction half-reaction (gain e-)
2Mg + O2 2MgO
4.15
Oxidized∴Reducing Agent (donates electrons
to oxygen and causes oxygen to
be reduced)
Reduced∴Oxidizing Agent (accepts electrons from Magnesium
and causes Magnesium to be
oxidized)
OIL RIG
Oxidation Is Loss
Reduction Is Gain
Zn (s) + CuSO4 (aq) ZnSO4 (aq) + Cu (s)
Zn is oxidizedZn Zn2+ + 2e-
Cu2+ is reducedCu2+ + 2e- Cu
Zn is the reducing agent
Cu2+ is the oxidizing agent
4.16
Copper wire reacts with silver nitrate to form silver metal.What is the oxidizing agent in the reaction?
Cu (s) + 2AgNO3 (aq) Cu(NO3)2 (aq) + 2Ag (s)
Cu Cu2+ + 2e-
Ag+ + 1e- Ag Ag+ is reduced Ag+ is the oxidizing agent
NaIO3
Na = +1 O = -2
3x(-2) + 1 + ? = 0
I = +5
IF7
F = -1
7x(-1) + ? = 0
I = +7
K2Cr2O7
O = -2 K = +1
7x(-2) + 2x(+1) + 2x(?) = 0
Cr = +6
Oxidation numbers of all the elements in the following ?
4.17
Types of Redox Reactions
(i) Combination Reaction
Two or more substances combine to form a single product.
0 0 +4 -2
S(s) + O2 (g) SO2(g)
(ii) Decomposition Reaction
Breakdown of a compound into two or more components.
+2 -2 0 0
2 HgO(s) 2Hg(l) + O2(g)
4.18
(iii) Displacement ReactionHalogen displacement
According to Activity Series
F2 > Cl2 > Br2 > I2i.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 0
Cl2 (g) + 2 KBr(aq) 2KCl(aq) + Br2(l)
0 -1 -1 0Cl2 (g) + 2 NaI(aq) 2NaCl(aq) + I2(l)
4.19
Ca2+ + CO32- CaCO3
NH3 + H+ NH4+
Zn + 2HCl ZnCl2 + H2
Ca + F2 CaF2
Precipitation
Acid-Base
Redox (H2 Displacement)
Redox (Combination)
Classify the following reactions.
4.20
4.5 Concentration of Solutions
concentration : amount of solute present in a given quantity of solvent or solution.
M = molarity =moles of solute
liters of solution
4.21
Most commonly used unit is “Molarity”
VnM =
Dilution is the procedure for preparing a less concentrated solution from a more concentrated solution.
DilutionAdd Solvent
Moles of solutebefore dilution (i)
Moles of soluteafter dilution (f)=
MiVi MfVf=4.22
How would you prepare 60.0 mL of 0.2 MHNO3 from a stock solution of 4.00 M HNO3?
MiVi = MfVf
Mi = 4.00 Mf = 0.200 Vf = 0.06 L Vi = ? L
4.23
Vi =MfVf
Mi= 0.200 x 0.06
4.00= 0.003 L = 3 mL
3 mL of acid + 57 mL of water = 60 mL of solution