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Reactions in Aqueous Solution. 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. Chapter 4 (semester 1/2009) prepared by A. Kyi Kyi Tin - PowerPoint PPT Presentation
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Reactions in Aqueous SolutionChapter 4 (semester 1/2009)prepared by A. Kyi Kyi Tin
Ref: Raymong Chang. Chemistry Ninth 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
4.1
4.1 General Properties of Aqueous Solutions
Solution = [ solute + solvent]
[smaller amount + larger amount]
[CLEAR, HOMOGENEOUS MIXTURE]
Aqueous solution = solute (liquid “or” solid) + 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/
reversible reaction
Ref: Raymond Chang Chemistry, Ninth Edition
Figure 4.1, Page 120
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, cannot conduct electricity (extremely weak electrolyte)
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 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
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
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
Hydronium ion, hydrated proton, H3O+
4.10
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!
Monoprotic acids
HCl 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 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) 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 Reactions
REDOX 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 means 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 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 0
Cl2 (g) + 2 KBr(aq) 2KCl(aq) + Br2(l)
0 -1 -1 0 Cl2 (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”
V
nM
Dilution is the procedure for preparing a less concentrated solution from a more concentrated solution.
Dilution
Add 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
Ref: power point presentation for instructors
(Mc- Graw hill series,www.mhhe.com/chemistry)