Transcript + H 2

Chemistry, The Central Science, 10th edition
Theodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten
Unit 4 (Chapter 4):
Aqueous Reactions &
Solution Stoichiometry
John D. Bookstaver
St. Charles Community College
St. Peters, MO
 2006, Prentice Hall, Inc.
Solutions:
+
• homogeneous mixtures:
evenly mixed (same)
• solvent is present in
greatest abundance.
• solute dissolved
in/by solvent
Molarity
• Molarity (M) is a measure of the
concentration of a solution.
moles of solute (mol)
Molarity (M) =
liters of solution (L)
units:
mol/L
or
–1
∙
mol L
What’s the concentration of a solution with
29.2 g of sodium chloride in 250. mL of water?
29.2 g NaCl x 1 mol NaCl = 0.500 mol NaCl = 2.00 M
58.44 g NaCl
NaCl
0.250 L
Solution Prep from Solid
1-Calc & Mass solute
WS #1-2
2-Add solvent, swirl to dissolve Conc.
Calc’s
3-Fill with DI water to mark
4-Mix (Cap & Invert to mix evenly)
WS Concentration & Dilutions
#1
5.00 g NaHCO3 x
1 mol NaHCO3 x
1 L NaHCO3
=
84.01 g NaHCO3 0.100 mol NaHCO3
0.595 L
NaHCO3
#2
1.20
mol
CuSO4
159.62
g
CuSO4
x
0.275 L CuSO4 x
1 L CuSO4
1 mol CuSO4
=
52.7 g
CuSO4
Solution Prep by Dilution
1-Calc M1V1=M2V2
M1V1 = M2V2
2-Pipet V1 from concentrated
WS #3-4
3-Fill to mark with DI water
Dilutions
4-Mix (Cap & Invert to mix evenly)
WS Concentration & Dilutions
M1V1 = M2V2 HW p.160 #60, 67
#3
M1V1 = M2V2
(12.0 M)V1 = (1.25 M)(500. mL)
V1 = 52.1 mL (or 0.0521 L)
#4
M1V1 = M2V2
(2.50 M)V1 = (0.200 M)(250. mL)
V1 = 20.0 mL (or 0.0200 L)
H
H
H
–
O
O
Cl
+
H
Cl
H
H
HCl + H2O  H3O+ + Cl–
 Acid: proton (H+) donor
 Base: proton (H+) acceptor
NH3 + H2O  NH4+ + OH–
H
H
H
N
H
O
H
H
N
H
H
–
+
H
O
H
Strength of Acids and Bases
STRONG: (complete ionization) (completely as ions)
HA(aq)
H+(aq) + A–(aq)
MOH(aq)
M+(aq) + OH–(aq)
WEAK: (partial ionization) (mostly as molecules)
HA(aq) + H2O(l)
H3O+(aq) + A–(aq)
B(aq) + H2O(l)
BH+(aq) + OH–(aq)
Only 6 strong acids:
Strong Acids:
• Nitric (HNO3)
HI + H2O  H3O+ + I– • Sulfuric (H SO )
2
4
proton (H+) donors
• Hydrochloric (HCl)
• Hydrobromic (HBr)
• Hydroiodic (HI)
• Perchloric (HClO4)
The strong bases are
Strong Bases:
soluble hydroxides
–) of…
(OH
–
+
OH + H3O  H2O + H2O
• Group 1 (Li,Na,K)
+
proton (H ) acceptors
• CBS (Ca, Ba, Sr)
Mg(OH)2 & Be(OH)2
are not soluble
Hydroxides of
Group I
and CBS
ase
Salts:
Ionic Solids: (metal-nonmetal)
dissociate (dissolve) by separation into ions
Electrolytes:
ions in solution that
conduct electricity
Non
Weak
C11H22O11
CH3OH
H2O
NO
ions
only
molecules
Strong
CH3COOH
HNO2
NH3
SOME
ions
NaOH
HNO3
KCl
ALL
ions
partially
completely
HW
ionize p.159 #33 dissociate
Electrolytes: Strong, Weak, or Non?
(ions conduct electricity)
metal-nonmetal
Compound
Ionic
HW p.157 #1,2,4,5,38
nonmetals (Covalent)
Molecular
Acid
(H____)
Not Acid
Weak
STRONG
Base
KBr
STRONG
WEAK
CaI2
NON
(& NH3)
(6)
FeCl3
C11H22O11
NaOH HCl, HBr, HI CH3COOH C2H5OH
HNO2
HNO3
Ca(OH)2
H2O
HF
(strong bases) H2SO4
HClO4
QUIZ!!!
(at the bell)
Electrolytes: Strong, Weak, or Non?
metal-nonmetal
Compound
nonmetals (Covalent)
Ionic
STRONG
Molecular
Acid
(H____)
STRONG
(6)
Weak
Base
WEAK
(& NH3)
Not Acid
NON
Acid-Base Neutralization Reactions
strong
acid
(H+A–)
strong
base
(M+OH–)
ionic
compound
(M+A–)
ACID + BASE
SALT + WATER
+
Cl
H
Na
O
water
H 2O
(HOH)
H
HCl(aq) + NaOH(aq)
Na
–
Cl
H
O
H
NaCl(aq) + H2O(l)
HW p.158 #40a
Precipitation Reactions
Double Replacement:
2 (aq) +
(aq)  2
(precipitate)
(aq) +
precipitate:
insoluble product
(as predicted by solubility rules)
Pb2+I–
( )
Solubility Rules
ALWAYS Soluble ions:
* Li+, Na+, K+, ...
+
NH
* 4
* NO3–
Group I (alkali metals)
ammonium
nitrate
Common Precipitates form with:
Ag+, Pb2+, Hg2+
(AP/H)
OH–
(hydroxide)
CO32–
(carbonate)
WS Solubility & NIE’s #1
examples
AgCl, PbI2
Cu(OH)2
CaCO3
Molecular Equation
• reactants and products in molecular form
AgNO3(aq) + KCl(aq)  AgCl(s) + KNO3(aq)
Ionic Equation
• Strong Electrolytes are Dissociated as ions
(strong acids, strong bases, soluble salts)
Ag+(aq) + NO3–(aq) + K+(aq) + Cl–(aq) 
AgCl(s) + K+(aq) + NO3–(aq)
Net Ionic Equation (NIE)
• Cross out Spectator Ions (no change)
(same state)
(same charge)
• only species left are those that react
(change) during the course of the reaction.
Ag+(aq) + NO3–(aq) + K+(aq) + Cl–(aq) 
Net
NIE:
AgCl(s) + K+(aq) + NO3–(aq)
Ag+(aq) + Cl–(aq)  AgCl(s)
Balanced Net Ionic Equations
comp – diss – cross – net – bal
1. Write a Complete molecular equation.
2. Dissociate all strong electrolytes(aq) .
(solubility rules)
3. Cross out spectators
(same charge & state)
4. Write the Net ionic equation with the
species that remain.
5. Balance the NIE.
Balanced Net Ionic Equations
comp – diss – cross – net – bal
+
2–
2+
–
+
–
1) (NH4)2SO4 + Ba(NO3)2 → BaSO4 + NH4NO3
Ba2+ + SO42– → BaSO4
+
–
2+
–
+ –
2) NaOH + MgBr2 → NaBr + Mg(OH)2
Mg2+ + 2 OH– → Mg(OH)2(s)
HW p.158 #21
Neutralization Reactions
When a Strong Acid reacts with a Strong Base,
the net ionic equation is…
H+ + OH–  H2O
HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l)
H+ + Cl– + Na+ + OH–  Na+ + Cl– + H2O
Neutralization Reactions
When a Weak acid reacts with a Strong base,
the net ionic equation is…
HX + OH–  X– + H2O
HF(aq) + KOH(aq)  KF(aq) + H2O(l)
(dissociate ONLY
STRONG electrolytes)
HF + Na+ + OH–  Na+ + F– + H2O
HW p.159 #40 (finish)
Balanced Net Ionic Equations
comp – diss – cross – net – bal
+
2–
2+
–
+
–
(NH4)2SO4 + Ba(NO3)2 → BaSO4 + NH4NO3
Ba2+ + SO42– → BaSO4(s)
+
–
+ –
HF(aq) + KOH(aq)  KF(aq) + H2O(l)
HF + OH–  F– + H2O
WS Solubility & NIE’s #2
Gas-Forming Reactions
H2 Demo
(M0)
(H+)
Single Rep: Metal + Acid
+
2–
Ex: Zn(s) + H2SO4(aq)
NIE: Zn(s) + 2 H+(aq)
(M+)
(gas)
Metal Ion + H2
2+ 2–
ZnSO4(aq) + H2(g)
Zn2+(aq) + H2(g)
(gas)
H2O(l) + CO2(g)
(CO32–)
CO2 Demo (H+)
Double Rep: Acid + Carbonate
Salt + H2CO3(aq)
(or Bicarbonate)
(decomposes
HW p. 159 #43
(HCO3–)
immediately)
Ex: HCl(aq) + CaCO3(s)
CaCl2(aq) + H2O(l) + CO2(g)
NIE: 2 H+(aq) + CaCO3(s)
Ca2+(aq) + H2O(l) + CO2(g)
CH3COOH + NaHCO3  CH3COONa + H2O + CO2
Solution Stoichiometry
Rxn:
gA
A(aq) + 2 B(aq)  C + 2 D
molar
mass A
g A
1 mol A
mol A
L of A
mol A
1L
mol-to-mol
ratio
gB
molarity
A (M)
HW p. 161 #81
g B
1 mol B
mol B
1L
molar
mass B
molarity
B (M)
mol B
L of B
Oxidation-Reduction Reactions
(REDOX)
video clip
(One
cannot
occur
without
the other)
LEO
says
GER
Oxidation Numbers
Is it a redox reaction? To find out…
1) assign oxidation numbers* (or oxidation states)
to each element in a reaction.
2) check if any oxidation states changed
(↓ reduced , ↑ oxidized)
*charges of ions show electrons
transferred IN an ionic compound
in Na2O,
O2–
*oxidation numbers of elements describe
electrons that would be lost or gained IF
the compound was 100% ionic.
in H2O,
O–2
Assigning Oxidation Numbers
1. All pure elements are 0
2. Monatomic ion is its charge (Mg2+ has +2)
3. Most nonmetals tend to be negative, but
some are positive in certain compounds or
ions. (in SO3 , O is –2 but S is +6)




O is −2 always but in peroxide ion is −1 (O22–)
H is +1 with nonmetals, −1 with metals
F is always −1.
other halogens are −1, BUT can be positive,
like in oxyanions.
Ex. ClO3– or NO3– or SO42–
Oxidation Numbers
• The sum of the ox. #’s in a neutral
compound is 0.
• The sum of the ox. #’s in a polyatomic ion
is the charge on the ion.
Determine the oxidation number of:
Sulfur in… SO2
Chromium in… K2Cr2O7
Nitrogen in… NH4+
Cobalt in… [CoCl6]3–
Classifying REDOX Reactions
All rxns (but…NOT double replacement)
Synthesis
A + B → AB
(0
0 → +/–)
Decomposition
2→1
AB → A + B
(+/– → 0 0)
1→2
Single Replacement
Combustion
AB + C → A + CB
(+/– 0 → 0
+/–)
CxHy + O2 → CO2 + H2O
(–/+
0 → +/–
+/–)
Single Replacement (REDOX)
silver ions
oxidize
copper metal
Cu(s) + 2 Ag+(aq)  Cu2+(aq) + 2 Ag(s)
+(aq)
Cu2+(aq) + 2 Ag(s) 
Cu
(s)
+
2
Ag
X
Cannot
displace H+
from acid to
make H2(g)
increasing ease of oxidation
Activity
Series
of
Metals
Writing REDOX Reactions
Write the net ionic equation for the reaction
of solid zinc in a solution of hydrochloric acid.
comp – diss – cross – net – bal
0
+1 –1
+2 –1
0
Mg(s) + HCl(aq)  MgCl2(aq) + H2(g)
Mg + 2 H+  Mg+2 + H2
Classify the reaction in two ways.
Single-Replacement and Redox
ox
Mg + 2 H+  Mg2+ + H2(g)
red
What is red & what is ox?
WS Aq Soln’s
& Chem Rxns