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