C h a p t e rC h a p t e r C h a p t e rC h a p t e r 4 4 Reactions in Aqueous Solution Chemistry, 5...
-
Upload
gwenda-craig -
Category
Documents
-
view
226 -
download
1
Transcript of C h a p t e rC h a p t e r C h a p t e rC h a p t e r 4 4 Reactions in Aqueous Solution Chemistry, 5...
C h a p t e rC h a p t e r 44Reactions in Aqueous SolutionReactions in Aqueous Solution
Chemistry, 5th EditionMcMurry/Fay
Chemistry, 5th EditionMcMurry/Fay
2
Some Interesting Chemical ReactionsSome Interesting Chemical Reactions
1. Production of Smog
N2 + O2 + heat → 2 NO
2 NO + O2 → 2 NO2 (brown gas)
2. The Greenhouse Effect
2 C8H18 + 25 O2 → 18 H2O + 16 CO2
CO2 transmits visible light but absorbs heat
3
Some Interesting Chemical ReactionsSome Interesting Chemical Reactions
3. Reduction of Iron Ore
Fe2O3 + 3 CO → 2 Fe + 3 CO2
4. Depletion of Ozone
O3 + uv rays → O2 + O
CF2Cl2 + O3 → O2 + O
4
Some Interesting Chemical ReactionsSome Interesting Chemical Reactions
5. Photosynthesis
6 CO2 + 6 H2O → C6H12O6 + 6 O2
6. Acid Rain
S + O2 + heat → SO2
SO2 + H2O → H2SO3 (acid)
5
Types of Chemical ReactionsTypes of Chemical Reactions
• Precipitation Reactions: The chemical reaction that occurs when two solutions are mixed and a solid precipitate is formed.
AgNO3 (aq) + NaCl (aq) → NaNO3 (aq) + AgCl (s)
6
Precipitation ReactionsPrecipitation Reactions
• Net Ionic Equations: Break the reaction down into aqueous ions and precipitates. Eliminates “spectator ions,” thus simplifying the equation.
AgNO3 (aq) + NaCl (aq) → NaNO3 (aq) + AgCl (s)
Ag+ + NO3- + Na+ + Cl- → AgCl (s) + Na+ + NO3
-
Net Ionic Equation: Ag+ + Cl- → AgCl (s)
7
Precipitation ReactionsPrecipitation Reactions
Solubility Rules
Always form soluble compounds:
Group 1 cations, NH4+, NO3
-
Often form precipitates:
Ag+, Hg22+, Pb2
2+
8
Types of Chemical ReactionsTypes of Chemical Reactions
• Acid–Base Reactions: A reaction of an acid with a base, forming water plus a salt.
• The driving force of this reaction is the formation of the stable water molecule.
HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)
9
Acid-Base ReactionsAcid-Base Reactions
• Arrhenius Definition:
1. Acid releases H+ in water.
HCl → H+ + Cl-
2. Base releases OH- in water
NaOH Na+ + OH-
10
Acid-Base ReactionsAcid-Base Reactions
• Brønsted Definition:
Acid donates a proton (H+), base accepts a proton.
HCl + H2O → H3O+ + Cl-
NH3 + H2O → NH4+ + OH-
11
Acid-Base ReactionsAcid-Base Reactions
• Lewis Definition:
Acid accepts 2 electrons, base donates 2 electrons.
(later)
12
pH - A Measure of Acidity pH - A Measure of Acidity
• The pH of a solution is defined as the negative logarithm of the hydrogen ion concentration (in mol/L).
pH = –log[H+]
pH + pOH = 14
Acidic solutions: [H+] > 1.0 x 10–7 M, pH < 7.00Basic solutions: [H+] < 1.0 x 10–7 M, pH > 7.00Neutral solutions: [H+] = 1.0 x 10–7 M, pH = 7.00
13
pH - A Measure of Acidity pH - A Measure of Acidity
• Calculate the pH of a HNO3 solution having a
hydrogen ion concentration of 0.76 M.
• The OH– ion concentration of a blood sample is
2.5 x 10–7 M. What is the pH of the blood?
14
Types of Chemical ReactionsTypes of Chemical Reactions
• Oxidation–Reduction (Redox) Reaction: A reaction in which one or more electrons are transferred between reaction partners.
Mg (s) + Cl2 (g) MgCl2(s)
15
Redox Reactions Redox Reactions
Electrolyte: a solution that conducts electricity
- or –
An ionic compound dissolved in water
16
Redox Reactions Redox Reactions
Strong electrolyte: almost all molecules are
ionized.
HCl, HNO3, NaCl
Weak electrolyte: only a small proportion of the
ions are formed.
H2SO3, HC2H3O2
17
Electrolytes in SolutionElectrolytes in Solution
• Why do ionic
compounds conduct
electricity when
molecular ones
generally do not?
18
Electrolytes in SolutionElectrolytes in Solution
• Electrolytes: Dissolve
in water to produce
ionic solutions.
• Nonelectrolytes: Do
not form ions when
they dissolve in water.
19
Electrolytes in SolutionElectrolytes in Solution
• Dissociation:
• The process by
which a compound
splits up to form ions
in the solution.
20
Redox Reactions Redox Reactions
How are electrons transferred??
Observe charges on elements:
Mg0 (s) + Cl20 (g) MgCl2(s)
Mg0 (s) + Cl20 (g) Mg2+ + 2Cl-
Mg0 → Mg2+ + 2 e- 2 e- + Cl20 → 2 Cl-
So electrons are TRANSFERRED from Mg to Cl2
21
Redox Reactions Redox Reactions
How are electrons transferred??
2 e- + Cl20 → 2 Cl-
Cl2 is REDUCED, since the charge on each Cl is lowered
Mg0 → Mg2+ + 2 e-
Mg is OXIDIZED, electrons are removed
REDuction + OXidation = REDOX
22
Redox Reactions Redox Reactions
Reducing Agent: causes reduction (donates electrons)
Oxidizing Agent: causes oxidation (accepts electrons)
2 Mg + O2 → 2 MgO
Oxidizing Agent = O2
Reducing Agent = Mg
23
Redox Reactions Redox Reactions
Electrochemical Series: A table showing the relative
oxidizing strengths of different species.
Helps to predict the outcome of unknown redox
reactions
Zn + Cu2+ → ??
Check Table…
24
Activity Series of ElementsActivity Series of Elements
25
Redox Reactions Redox Reactions
Zn + Cu2+ → ??
From Table: Zn is a stronger reducing agent than Cu.
Therefore the electrons are more likely to reside with Cu
in the product:
Zn + Cu2+ → Zn2+ + Cu
26
Redox Reactions Redox Reactions
OXIDATION NUMBER
Effective charge on any atom
NaCl: Na +1, Cl -1
MgCl2: Mg +2, Cl -1
H2O: H +1, O -2
MgO: Mg +2, O -2
27
Redox Reactions Redox Reactions
CALCULATING OXIDATION NUMBER
1. The sum of the O.N.s of all of the atoms in a molecule
or ion is equal to its total charge.
NaCl: ONNa + ONCl = 0 +1 + (-1) = 0
SO42-: ONS + 4 x ONO = -2 6 + 4x(-2) = -2
28
Redox Reactions Redox Reactions
CALCULATING OXIDATION NUMBER
2. For atoms in the elemental form the oxidation number
is zero.
Mg (s): ON = 0
O2 (g): ON = 0
29
Redox Reactions Redox Reactions
CALCULATING OXIDATION NUMBER
3. Remember some common oxidation numbers:
Group 1 → +1
Group 2 → +2
Halogens → -1
Oxygen → -2
Hydrogen → +1, -1
30
Redox Reactions Redox Reactions
CALCULATING OXIDATION NUMBER
HSO3- ONS = ??
ONH + ONS + 3(ONO) = -1
ONH = +1, ONO = -2
So ONs = -1 – (1) – (3 x (-2)) = +4
31
Redox Reactions Redox Reactions
HALF REACTIONS
Mg + Cl2 → MgCl2
Find ON of each atom:
Mg0 + Cl20 → Mg2+Cl2
1-
Break reaction into two separate (HALF) reactions
showing electrons
32
Redox Reactions Redox Reactions
HALF REACTIONS
Mg + Cl2 → MgCl2
Break reaction into two separate (HALF) reactions
showing electrons
Mg0 → Mg2+ + 2 e-
Cl20 + 2 e- → 2 Cl-
33
Balancing Redox Reactions Balancing Redox Reactions
HALF REACTION METHOD
1. Break reaction into half reactions.
2. Balance each half reaction separately.
a) use H+ and H2O as needed in ACIDIC solution.
b) use OH- and H2O as needed in BASIC solution.
3. Balance charge in each half reaction by adding
electrons to one side of the equation.
34
Balancing Redox Reactions Balancing Redox Reactions
HALF REACTION METHOD
4. Obtain equal number of electrons in each half reaction
by multiplying entire equation by a constant.
5. Add the 2 half reactions back together so that the
electrons cancel.
35
Balancing Redox ReactionsBalancing Redox Reactions
• Balance the following for acidic and basic solution:
ClO–(aq) + Cr(OH)4–(aq) CrO4
2–(aq) + Cl–(aq)
NO3–(aq) + Cu(s) NO(g) + Cu2+(aq)
MnO4–(aq) + IO3
–(aq) MnO2(s) + IO4–(aq)