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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:

evenly mixed (same)

• solvent is present in greatest abundance.

• solute dissolvedin/by solvent

+

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’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

58.44 g NaCl= 0.500 mol NaCl = 2.00 M

NaCl

Solution Prep from Solid1-Calc & Mass solute

2-Add solvent, swirl to dissolve

3-Fill with DI water to mark

4-Mix (Cap & Invert to mix evenly)

WS #1-2

Conc.

Calc’s

WS Concentration & Dilutions

0.100 mol NaHCO3

5.00 g NaHCO3 x 1 mol NaHCO3

84.01 g NaHCO3

x 1 L NaHCO3 =

0.595 L

NaHCO3

#1

1 mol CuSO4

0.275 L CuSO4 x 1.20 mol CuSO4

1 L CuSO4

x 159.62 g CuSO4 =

52.7 g

CuSO4

#2

1-Calc M1V1=M2V2

2-Pipet V1 from concentrated

3-Fill to mark with DI water

4-Mix (Cap & Invert to mix evenly)

M1V1 = M2V2

Solution Prep by Dilution

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 (or 0.0521 L)

M1V1 = M2V2

(2.50 M)V1 = (0.200 M)(250. mL)

V1 = 20.0 mL (or 0.0200 L)

HW p.160 #60, 67

HCl + H2O → H3O+ + Cl–

H

H H

H

HHO OCl Cl

+ –

NH3 + H2O → NH4+ + OH–

H

H

H

H

H

H

HH

H H

N O ON

+ –

�Acid: proton (H+) donor

�Base: proton (H+) acceptor

Strength of Acids and Bases

(complete ionization) (completely as ions)

HA(aq) H+(aq) + A–(aq)

MOH(aq) M+(aq) + OH–(aq)

(partial ionization) (mostly as molecules)

HA(aq) + H2O(l) H3O+(aq) + A–(aq)

B(aq) + H2O(l) BH+(aq) + OH–(aq)

STRONG:

WEAK:

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 & Be(OH)2

are not soluble

proton (H+) acceptors

OH– + H3O+ � H2O + H2O

aseHydroxides of

Group I

and CBS

Salts:Ionic Solids: (metal-nonmetal)dissociate (dissolve) by separation into ions

Electrolytes:ions in solution that conduct electricity

StrongWeak

C11H22O11

CH3OH

H2O

Non

CH3COOH

HNO2

NH3

NaOH

HNO3

KCl

completely

dissociate

partially

ionize

only

molecules

NOions

ALLions

SOMEions

HW

p.159 #33

Electrolytes: Strong, Weak, or Non?

Compound

Ionic

STRONG

Molecular

Acid

(H____)

STRONG

(6)

WEAK

Not Acid

NON

HW p.157 #1,2,4,5,38

nonmetals (Covalent)metal-nonmetal

C11H22O11

C2H5OH

H2O

CH3COOH

HNO2

HF

KBr

CaI2FeCl3NaOH

Ca(OH)2

(strong bases)

HCl, HBr, HI

HNO3

H2SO4

HClO4

(ions conduct electricity)

Weak

Base

(& NH3)

Electrolytes: Strong, Weak, or Non?Compound

Ionic

STRONG

Molecular

Acid

(H____)

WEAK

Not Acid

NON

nonmetals (Covalent)metal-nonmetal

STRONG

(6)

QUIZ!!!(at the bell)

Weak

Base

(& NH3)

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.159 #40a

2 (aq) + (aq) ���� 2 (aq) + ( )

Double Replacement: (precipitate)

precipitate:insoluble product(as predicted by solubility rules)

Precipitation Reactions

Pb2+

I–

ALWAYS Soluble ions:

Li+, Na+, K+, ... Group I (alkali metals)

NH4+ ammonium

NO3– nitrate

Solubility Rules

Common Precipitates form with: examples

Ag+, Pb2+, Hg2+ (AP/H) AgCl, PbI2OH– (hydroxide) Cu(OH)2

CO32– (carbonate) CaCO3

*

*

*

WS Solubility & NIE’s #1

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)

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 (no change)

• only species left are those that react(change) during the course of the reaction.

Net

(same state)(same charge)

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.

5. Balance the NIE.

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 + K+ + OH–→ K+ + F– + H2O

Neutralization Reactions

HX + OH–→→→→ X– + H2O

HW p.159 #40 (finish)

When a Weak acid reacts with a Strong base,

the net ionic equation is…

(dissociate ONLY

STRONG electrolytes)

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)

(decomposes

immediately)

(gas)

CO2 Demo

g A L of A

g B mol B L of B

g A

1 mol Amol A

1 L

g B

1 mol B

mol B

1 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

(Onecannotoccur 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.

*oxidation numbers

*charges

in H2O,

O–2

of ions show electrons

transferred IN an ionic compound

in Na2O,

O2–

� F is always −1.

� other halogens are −1, BUT can be positive, like in oxyanions.

Ex. ClO3– or NO3

– or SO42–

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, butsome are positive in certain compounds or ions.� O is −2 always

� H is +1 with nonmetals, −1 with metals

O is –2 but S is +6)(in SO3 ,but in peroxide ion is −1 (O2

2–)

Oxidation Numbers

• The sum of the ox. #’s in a neutralcompound 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)

Decomposition

AB → A + B 1 → 2

(+/– → 0 0)

CombustionCxHy + O2 → CO2 + H2O

(–/+ 0 → +/– +/–)

Single ReplacementAB + C → A + CB

(+/– 0 → 0 +/–)

Synthesis

A + B → AB 2 → 1

(0 0 → +/–)

Single Replacement (REDOX)

Cu2+(aq) + 2 Ag(s) → Cu(s) + 2 Ag+(aq)X

Cu(s) + 2 Ag+(aq) → Cu2+(aq) + 2 Ag(s)

silver ions

oxidize

copper metal

Activity

Series

of

Metals

incre

asin

g e

ase

of

oxid

atio

n

Cannotdisplace H+

from acid to

make H2(g)

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 – bal

0 +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 Aq Soln’s& Chem Rxns

What is red & what is ox?red

ox