unit 4 (chapter 4): aqueous reactions & solution stoichiometry john d. bookstaver st. charles...
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Unit 4 (Chapter 4):
Aqueous Reactions & Solution Stoichiometry
John D. Bookstaver
St. Charles Community College
St. Peters, MO
2006, Prentice Hall, Inc.
Chemistry, The Central Science, 10th editionTheodore L. Brown; H. Eugene LeMay, Jr.; and Bruce E. Bursten
Solutions:
• homogeneous mixtures.
( _____ throughout)
• solvent is present in greatest abundance.
• solute dissolved in/by solvent
+ same
0.250 L
Molarity• Molarity (M) is a measure of the
concentration of a solution.
moles of solute (mol)
liters of solution (L)Molarity (M) =
units:mol/L or mol∙L–1
What is the molarity of a solution with 29.2 g of sodium chloride in 250. mL of water?
29.2 g NaCl x 1 mol NaCl58.44 g NaCl
= 0.500 mol NaCl = 2.00 MNaCl
Preparing a Solution
1-mass solute2-add solvent, swirl to dissolve
3-add solvent to mark
WS #1-2 Conc. Calc’s
HW p.160 #60, 67
WS Concentration & Dilutions
0.100 mol NaHCO3
5.00 g NaHCO3 x1 mol NaHCO3
84.01 g NaHCO3
x 1 L NaHCO3 =
0.595 LNaHCO3
#1
1 mol CuSO4
0.275 L CuSO4 x1.20 mol CuSO4
1 L CuSO4
x 159.62 g CuSO4 =
52.7 gCuSO4
#2
Dilution M1V1 = M2V2
1-calc M1V1=M2V2
2-pipet V1 from concentrated
3-fill to mark w DI
Dilution M1V1 = M2V2
What volume of water must be added to prepare 2.0 L of 3.0 M CuSO4 from a stock solution of concentration 8.0 M ?
WS #3-4 Dilutions
WS Concentration & Dilutions
#3
#4
M1V1 = M2V2
M1V1 = M2V2
(12.0 M)V1 = (1.25 M)(500 mL)
V1 = 52.1 mL (0.0521 L)
M1V1 = M2V2
(2.50 M)V1 = (0.200 M)(250 mL)
V1 = 20.0 mL (0.0200 L)
HCl + H2O H3O+ + Cl–
H
H H
H
HHO OCl Cl
+ –
NH3 + H2O NH4+ + OH–
HH
H
H
H
H
HHH H
N O ON
+ –
Acid: proton (H+) donorBase: proton (H+) acceptor
Strength of Acids and Bases
STRONG (complete dissociation)
HA(aq) + H2O(l) H3O+(aq) + A–(aq)
B(aq) + H2O(l) BH+(aq) + OH–(aq)
WEAK (partial dissociation)
HA(aq) + H2O(l) H3O+(aq) + A–(aq)
B(aq) + H2O(l) BH+(aq) + OH–(aq)
Strong Acids: Only 6 strong acids:• Nitric (HNO3)
• Sulfuric (H2SO4)
• Hydrochloric (HCl)• Hydrobromic (HBr)• Hydroiodic (HI)• Perchloric (HClO4)
proton (H+) donors
HI + H2O H3O+ + I–
Strong Bases: The strong bases are soluble hydroxides
(OH–) of…• Group 1 (Li,Na,K)• CBS (Ca, Ba, Sr)
Mg(OH)2 not as soluble
proton (H+) acceptors
OH– + H3O+ H2O + H2O
ase
Salts:Ionic Solids: (metal-nonmetal)dissociate (dissolve) by separation into ions
Electrolytes:ions in solution that conduct electricity
StrongWeak
C11H22O11
CH3OHH2O
Non
CH3COOHHNO2
NH3
NaOHHNO3
KCl
completely dissociate
partially ionize
only molecules
NOions
ALLions
SOMEions
HWp.159 #33
Electrolytes: Strong, Weak, or Non?
Compound
Ionic
STRONG
Molecular
Acid(H____)
STRONG(6)
WEAK(& NH3)
Not Acid
NON
HW p.157-159 #1,2,4,5,38
nonmetals (Covalent)metal-nonmetal
C11H22O11
C2H5OHH2O
CH3COOHHNO2
HF
KBrCaI2
FeCl3NaOH
Ca(OH)2
(strong bases)
HCl, HBr, HIHNO3
H2SO4
HClO4
(ions conduct electricity)
Electrolytes: Strong, Weak, or Non?Compound
Ionic
STRONG
Molecular
Acid(H____)
WEAK(& NH3)
Not Acid
NON
nonmetals (Covalent)metal-nonmetal
STRONG(6)
QUIZ!!!(at the bell)
ClNaHONa
strong acid
(H+A–)
strong base
(M+OH–)
HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)
ACID + BASE SALT + WATER
H HHOCl
+ –
ioniccompound
(M+A–)
waterH2O
(HOH)
Acid-Base Neutralization Reactions
HW p.158 #40a
2 KI(aq) + Pb(NO3)2(aq) 2 KNO3(aq) + PbI2(s) Double Replacement: (precipitate)
precipitate:insoluble ionic compound(as predicted by solubility rules)
Precipitation Reactions
Pb2+I–
ALWAYS Soluble Ions:Na+, K+, etc. group I (alkali metals)
NH4+ ammonium
NO3– nitrate
HCO3– bicarbonate
C2H3O2– (CH3COO–) acetate (ethanoate)
ClO3–, ClO4
– chlorate, perchlorate
Solubility Rules
Common Precipitates form with: examples
Ag+, Pb2+, Hg2+ (AP/H) AgCl, PbI2
OH– (hydroxide) Cu(OH)2
CO32– (carbonate) CaCO3
***
WS Solubility & NIE’s #1
Molecular Equation
The molecular equation lists the reactants and products in their molecular form.
AgNO3(aq) + KCl(aq) AgCl(s) + KNO3(aq)
Ionic Equation• In the ionic equation all strong electrolytes
(strong acids, strong bases, and soluble ionic salts) are dissociated into their ions.
• This more accurately reflects the species that are found in the reaction mixture.
Ag+(aq) + NO3
–(aq) + K+
(aq) + Cl–(aq)
AgCl(s) + K+(aq) + NO3
–(aq)
AgNO3(aq) + KCl(aq) AgCl(s) + KNO3(aq)
Net Ionic Equation
Ag+(aq) + NO3
–(aq) + K+
(aq) + Cl–(aq)
AgCl(s) + K+(aq) + NO3
–(aq)
NIE: Ag+(aq) + Cl–(aq) AgCl(s)
• Cross out Spectator Ions that do not change (same state & same charge) from the left side of the equation to the right.
• The only species left are those things that react (change) during the course of the reaction.
Balanced Net Ionic Equations
1. Write a complete molecular equation.
2. Dissociate all strong electrolytes (aq) .
3. Cross out spectators (same charge & state)
4. Write the net ionic equation with the species that remain and balance it.
comp – diss – cross – net – bal
(solubility rules)
BaSO4 + NH4NO3
Balanced Net Ionic Equations
1) (NH4)2SO4 + Ba(NO3)2 →
2) NaOH + MgBr2 →
comp – diss – cross – net – bal
+ 2– 2+ –– +
Ba2+ + SO42– → BaSO4
NaBr + Mg(OH)2
+ – 2+ –– +
Mg2+ + 2 OH– → Mg(OH)2(s)
HW p.158 #21
HCl(aq) + NaOH(aq) NaCl(aq) + H2O(l)
H+ + Cl– + Na+ + OH– Na+ + Cl– + H2O
Neutralization Reactions
H+ + OH– H2O
When a Strong Acid reacts with a Strong Base, the net ionic equation is…
HF(aq) + KOH(aq) KF(aq) + H2O(l)
HF + Na+ + OH– Na+ + F– + H2O
Neutralization Reactions
HX + OH– X– + H2O
When a Weak reacts with a Strong, the net ionic equation is…
HW p.159 #40 (finish)
BaSO4 + NH4NO3
Balanced Net Ionic Equations
(NH4)2SO4 + Ba(NO3)2 →
comp – diss – cross – net – bal
+ 2– 2+ –– +
Ba2+ + SO42– → BaSO4(s)
HF(aq) + KOH(aq) KF(aq) + H2O(l)
WS Solubility & NIE’s #2
HF + OH– F– + H2O
–+–+
Gas-Forming Reactions
Single Rep: Metal + Acid Metal Ion + H2
Ex: Zn(s) + H2SO4(aq) ZnSO4(aq) + H2(g)
NIE: Zn(s) + 2 H+(aq) Zn2+(aq) + H2(g)
H2 Demo (M0) (H+) (M+) (gas)
+ 2– 2+ 2–
Double Rep: Acid + Carbonate Salt +
Ex: HCl(aq) + CaCO3(s) CaCl2(aq) + H2O(l) + CO2(g)
NIE: 2 H+(aq) + CaCO3(s) Ca2+(aq) + H2O(l) + CO2(g)
(or Bicarbonate)(HCO3
–)
(CO32–)(H+)
CH3COOH + NaHCO3 CH3COONa + H2O + CO2
HW p. 159 #43
H2CO3(aq)
H2O(l) + CO2(g)
(decomposesimmediately)
(gas)
CO2 Demo
g A L of A
g B mol B L of B
g A1 mol A
mol A1 L
g B1 mol B
mol B1 L
molar mass A
molar mass B
molarity A (M)
molarity B (M)
mol-to-mol ratio
mol A
Rxn: A(aq) + 2 B(aq) C + 2 D
Solution Stoichiometry
HW p. 161 #81
Oxidation-Reduction Reactions(REDOX)
video clip
(Onecannot occur withoutthe 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)
of elements describe electrons that would be lost or gained IF the compound was 100% ionic.
of ions show electrons transferred IN an ionic compound
*oxidation numbers
*charges
F is always −1. other halogens are −1, but can be positive,
like in oxyanions.
Ex. ClO3– or NO3
– or SO42–
Assigning Oxidation Numbers1. All elements are 0. (all compounds are 0)
2. Monatomic ion is its charge. (Ex. Na+ ion)
3. Most nonmetals tend to be negative, but some are positive in certain compounds or ions. (Ex. SO3)
O is −2 always, but in peroxide ion is −1 (O2–2).
H is +1 with nonmetals, −1 with a metals.
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.
Calculate the oxidation number of each:
Sulfur in… SO3
Chromium in… K2Cr2O7
Nitrogen in… NH4+
Cobalt in… [CoCl6]3–
Classifying REDOX Reactions
All rxns (but…NOT double replacement)
DecompositionAB → A + B 1 →
2(+/– → 0 0)
CombustionCxHy + O2 → CO2 + H2O
(–/+ 0 → +/– +/–)
Single ReplacementAB + C → A + CB(+/– 0 → 0 +/–)
SynthesisA + B → AB 2 →
1(0 0 → +/–)
Single Replacement (REDOX)
Cu2+(aq) + 2 Ag(s) Cu(s) + 2 Ag+(aq) XCu(s) + 2 Ag+(aq) Cu2+(aq) + 2 Ag(s)
silver ions
oxidize
copper metal
Activity Series
of Metals
incr
easi
ng e
ase
of o
xida
tion
Cannot displace H+ from acid to make H2(g)
Write an overall equation for the synthesis of calcium sulfide from its elements. Then write the RED and OX half-equations to identify the REDOX process.
Writing REDOX Reactions
Ca + S CaS
Ca0 Ca+2
0 +2 –20
OX:
RED: S0 S–2
+ 2 e–
2 e– +
Ca + S CaS
4 Al+3 4 Al012 e– +
O–2 3 O20 + 12 e–
4 ( )
3 ( )
Writing REDOX ReactionsWrite an overall equation for the decomposition of aluminum oxide into its elements. Then write the RED and OX half-equations to identify the REDOX process.
Al2O3 Al + O2
O–2 O20
0+3 –2 0
OX:
RED: Al+3 Al0
+ 4 e–
3 e– +
2 Al2O3 4 Al + 3 O2
26
Write the net ionic equation for the reaction of solid zinc in a solution of hydrochloric acid.
Writing REDOX Reactions
Mg(s) + HCl(aq) MgCl2(aq) + H2(g)
comp – diss – cross – net – bal0 +1 –1 +2 –1 0
Mg + H+ Mg+2 + H22
Classify the reaction in two ways.
Single-Replacement and Redox
Mg + 2 H+ Mg2+ + H2(g)
WS 5c #1-2
What is red & what is ox?red
ox