1a03-2011-ch5_full-notes

1

CHEM 1A03: Intro. Chemistry I

Water & Aqueous Chemistry

Ch.5: Reactions in Aqueous Solutions

http://en.wikipedia.org/wiki/Thermite

http://visibleearth.nasa.gov/view_rec.php?id=2429

http://en.wikipedia.org/wiki/Iron_blast_furnace

http://www.chem1.com/CQ/

?http://www.scienceinafrica.co.za/2004/july/fluoride.htm

2

Water: A Vital Natural Resource!

Significance of Water: Energy, Health & Environment“No single measure would do more to reduce disease and save lives

in the developing world than bringing safe water & adequate sanitation to all.”

UN Secretary-General Kofi Annan, 2003 International Year of Freshwater

“Water is probably the only natural resource to touch all aspects of human civilization —from agricultural and industrial development to

the cultural & religious values embedded in society.”

Koichiro Matsuura, Director-General, UNESCO

http://en.wikipedia.org/wiki/Waterfall http://en.wikipedia.org/wiki/Desert en.wikipedia.org/wiki/Hurricane

http://en.wikipedia.org/wiki/Drinking_water

en.wikipedia.org/wiki/Bottled_water

3

Water: An Enigmatic Medium!

Unique Macroscopic Properties Essential to Life

1. Unusually high boiling point (b.p.) of liquid water at STP: bp = 100oC at 1 atm (Sea level) T,P-dependent

2. Density of ice (0.92 g/mL) < liquid water (1 g/mL) at 0oC:Ice expands with freezing: Lower packing density

3. High specific heat capacity of water (74 J/mol.K at STP): Absorbs thermal heat for storage/distribution/release

4. Water dissolves a variety of solutes as a solvent:Strong solvation properties for most polar molecules/ions

41 Anomalies of Water: http://www.lsbu.ac.uk/water/anmlies.html

http://visibleearth.nasa.gov/view_rec.php?id=2429

en.wikipedia.org/wiki/Iceberg

en.wikipedia.org/wiki/Snowflak

4

iClicker Question #1iClicker Question #1Which intermolecular force accounts for water’s unusual high b.p.?

(a) Ion-dipole

(b) Dipole-dipole

(c) H-bonding

(d) Van der Waals

(e) none of the above

Hydrogen bonds: possible because

of water’s extreme polarity

OH H

Molecular Dipole

•• ••

Fig. 5-1a, p. 152 (143, 9th ed.)

5

Solubilization of polar/ionic solutes: Hydration

Energetically favorable H2O-solute interactions:H-bonding (dipole-dipole) with solutes (O-H, N-H , C=O)+/- ion-dipole forces

Solute Solvation by Water

CH3CH2O-H

Dipole-dipole interactions

Na+-

+

+

-+

+ +

+

+

+

+

++

+

-

-

- -

Ion-dipole interactions

Cl--

+

+

-

+

++

+

+

+

+

++

-

-

-

Hydration shell

+-

..

..

6

Properties of Water Vital for Molecular Behaviour

Protein Folding, Activity & Drug Binding

Human Serum Albumin (HSA)

Ion Hydration, Sodium Pumps & Ion Transport

Sodium Ion

Dichlorodiphenyl-trichloroethane (DDT)

Solubility, Toxicity & BioaccumulationCl Cl

ClCl

Cl

7

Water auto-ionization: Water is amphoteric & conductive

Auto-ionization of Water

2H2O (l) H3O+ (aq) + OH- (aq)Kw Water acts as acid

& base with itself!

Kw = [H3O+][OH-]= 1 x 10-14 (25oC)

Purified De-ionized Water:

pH = -log[H3O+] = 7.0 Low conductivity since [H3O+] & [OH-] = 0.1 M

Electrolytes

Why isn’t [H2O] included in equilibrium expression?

H

H

O

H HO

H H

H ..O H

-+

O

H

OH H

Base

Acid Hydronium

Hydroxide

Transition State

..

8

Solute Properties & Electrolytes

Non-electrolyte Strong electrolyte Weak electrolyte

Neutral molecule Fully charged ions Partially ionized molecule

Degree of ionization of an electrolyte in aqueous solution!

Fig. 5-3, p. 152-155 (143- 146, 9th ed.)

9

Solutes as Electrolytes

1. Strong electrolyte (Ionic)Sodium Chloride:

3. Non-electrolyte (Neutral)Ethanol: Vodka (> 40% v) Spirit, Depressant &

Diuretic

2. Weak electrolyte (Weakly Ionic)Acetic Acid: Vinegar (5-8% w)

Preservative/Sour

Conductive ions

CH3COOH (aq) + H2O (l) CH3COO- (aq) + H3O+ (aq)Ka = 4.8p

NaCl(aq) Na+(aq) + Cl(aq)

Intravenous supply of electrolytes

pKa = 16 No ionizationCH3CH2OH

10

iClicker Question #2iClicker Question #2

(a) NaBr (aq, 1M)

(b) CH3OH (l)

(c) CH3COOH (aq, 1M)

(d) (NH4)2SO4 (aq, 1M)

(e) H2O (l)

Which of the following would be the strongest conductor of electricity?

11

1. Solubility or Precipitation Reactions: (ion transfer)

2. Reduction-Oxidation (Redox) Reactions: (electron transfer)

3. Acid-Base Reactions: (proton transfer)

Major Types of Aqueous Chemical Reactions

Zn (s) + Cu2+ (aq) Zn2+ (aq) + Cu (s)

CH3COOH (aq) + H2O (l) CH3COO- (aq) + H3O+ (aq)

K is a measure of extent of chemical reaction & transformation!

Cu(NO3)2(aq) + 2 NaOH(aq) Cu(OH)2(s) + 2 NaNO3(aq)

Lab 2

Lab 2

12

Solubility: Qualitative Guidelines

Table 5-1; p. 156-159 (146-149, 9th ed.)

Soluble: Strong Electrolytes (Ksp >> 1)

Insoluble: Weak Electrolytes (Ksp << 1)

KI (aq) K+ (aq) + I- (aq)

CdCO3 (s) Cd2+ (aq) + CO32- (aq)

“slightly soluble” = soluble

13

Net Ionic Reaction

Precipitation of AgI (s)

AgNO3 (aq) + KI (aq) AgI (s) + KNO3 (aq)

AgI (s)Ag+ (aq) + I- (aq)

Net Ionic Equation

or

AgI (s) + K+ (aq) + NO3- (aq)Ag+ (aq) + NO3

- (aq) + K+ (aq) + I- (aq)Spectator Ions

Derived from Strong Electrolytes

p. 157 (147, 9th ed.)

Total Ionic Equation

14

Practice Exercise & Solution

Practice Question:

Determine the mass of KI needed to precipitate 0.1 mM of AgNO3 in a 20 mL sample solution.

Balanced equation:AgNO3 (aq) + KI (aq) AgI (s) + KNO3(aq)

Moles of AgNO3 present in solution:(1 x 10-4 moles/L) x (2 x 10-2 L) = 2 x 10-6 moles of AgNO3

moles of KI = moles of AgNO3, from the balanced reaction.

Mass of KI = 2 x 10-6 moles x 166.0 g/mol = 0.3 mg

15

Solubility & Precipitation: Demo#1

Ksp = 8.3 x 10-17

Solubility Product (defined by Ksp)

PrecipitationK = 1/Ksp = 1.2 x 1016

AgI (s)Ksp

Ag+ (aq) + I- (aq)

AgI (s)1/Ksp

Ag+ (aq) + I- (aq)

AgNO3 (aq) NaI (aq) AgI (s) + NaNO3 (aq)Fig. 5-7 (5-4 9th ed.)

16

Solubility & Precipitation: Demo#2

Fig. 18-1, pg 752

Ksp = 7.1 x 10-9PbI2 (s) Pb2+ (aq) + 2I- (aq)Ksp

iClicker Question #3

What would be the impact of dissolving PbI2 in a 1.0 M solution of Pb(NO3)2?

a.Increase the solubility

b.Decrease the solubility

c.No effect on equilibrium

17

Measure of the intrinsic solubility of a salt in aqueous solution Also temp., pH, ionic strength dependent; Ksp in pure water

A low Ksp << 1 implies a sparingly soluble or highly insoluble salt

Which form of apatite is least soluble & most resistantto demineralization (tooth decay)?

Solubility Product for Salts: Ksp

Ca5(PO4)3OH (s)Ksp

5Ca2+ (aq) + 3PO43- (aq) + OH- (aq)

Hydroxylapatite

Fluorapatite

Ca5(PO4)3F (s)Ksp

5Ca2+ (aq) + 3PO43- (aq) + F- (aq)

Ksp = [Ca2+]5 [PO43-]3 [OH-] = 1.0 x 10-36

Ksp = [Ca2+]5 [PO43-]3 [F-] = 1.0 x 10-60

en.wikipedia.org/wiki/Human_tooth

18

Differential Solubility of Salts

Ca5(PO4)3OH (s)Ksp

5Ca2+ (aq) + 3PO43- (aq) + OH- (aq)

Hydroxylapatite:

Ksp = [Ca2+]5 [PO43-]3 [OH-] = 1.0 x 10-36

Determine the Relative Decrease in Solubility of Fluorapatite vs. Hydroxylapatite

Let x = [OH-] formed upon dissolution

Ksp = (5x)5 (3x)3 (x) = 84375 x9

x = [Ksp/84375] 1/9 = 2.84 x 105 MMolar solubility of

hydroxylapatite

19

Differential Solubility of Salts…contd

2.84 x 105 M = 4606.11 x 108 M

Similarly, for Fluorapatite:

Ksp = [Ca2+]5 [PO43]3 [F] = 1.0 x 1060

Ca5(PO4)3F (s)Ksp

5Ca2+ (aq) + 3PO43- (aq) + F- (aq)

Hydroxylapatite 460-fold more soluble than fluorapatite

x = [Ksp/84375] 1/9 = 6.11 x 108 M

Let x = [F] formed upon dissolution

Ksp = (5x)5 (3x)3 (x) = 84375 x9

20

What is the molar solubility of cobalt (II) hydroxide (Ksp = 1.6 x 10-15)?

Co(OH)2 Co2+ + 2OH−

a. 6.1 x 10-6

b. 9.3 x 10-6 Ksp = [x][2x]2

c. 8.7 x 10-6 1.6 x 10-15 = 4x3

d. 7.4 x 10-6 x = 7.4 x 10-6

e. 1.1 x 10-6

Take Home ProblemTake Home Problem

21

Application: Low Cost Defluoridation Method

Inexpensive, renewable and low cost method needed for defluoridation of drinking water in villages of developing countries

Ion-exchange process uses charred animal bone that is pulverized, filtered & washed for defluoridation via F- adsorption

Ca5(PO4)3OH (s) + F- (aq)Kex

Ca5(PO4)3F (s) + OH- (aq)Ion-exchange Mechanism

Regenerated with NaOH & H2O washRock/Pebble Layer

Charred Bone Layer

Charcoal/C

Fluoridated Water

Treated Water

Filtration Device

Water

Also effective for adsorbing

Pb, As, Hg

http://www.scienceinafrica.co.za/2004/july/fluoride.htm

22

Q vs Ksp: Practice Question

Precipitation of PbS (s): Lead Contamination

Will a precipitate form if 0.50 mL of 10 M of K2S is mixed with 250 mL of 0.10 M Pb(NO3)2 ?

K2S (aq) + Pb(NO3)2 (aq) 2KNO3 (aq) + PbS (s)

Ksp = [Pb2+] [S2-] = 3.0 x 10-29

PbS (s) Pb2+ (aq) + S2- (aq)Ksp

Initial Concentration of K2S After Mixing Solutions:

Initial Concentration of Pb(NO3)2After Mixing Solutions:

= (1x10-5 mol/L*5x10-4 L) / 2.505x10-1 L

= 1.996 x 10-8 M

= (1x10-7 mol/L*2.50x10-1 L) / 2.505x10-1 L

= 9.980 x 10-8 M

Q = [Pb2+][S2-] = (9.98 x 10-8)(1.996 x 10-8) = 2.0 x 10-15 >> Ksp

Therefore, precipitate of PbS (s) will form!

www.cbc.ca/news/background/water/lead-pipes.htmlhttp://www.sxc.hu/photo/158242

23

What is the value for Qsp if 0.500 mL of 1.50M BaCl2 is mixed with 0.600 mL of 0.20M NaOH?

a. 8.1 x 10-3

b. 7.7 x 10-3

c. 2.3 x 10-3

d. 9.1 x 10-2

e. 7.4 x 10-2

iClicker Questions #4 & #5iClicker Questions #4 & #5

If the Ksp for Ba(OH)2 is 5 x 10-3, will a precipitate form?

a.Yesb.No

24Ch 5-2, p. 159 (p. 149, 0th ed.)

Which of the following reactions will result in formation of a precipitate?

NaOH (aq) + MgCl2 (aq)

(NH4)2SO4 (aq) + ZnCl2 (aq)

BaS (aq) + CuSO4 (aq) CuS (s) + BaSO4 (s)

ZnSO4 (aq) + 2NH4Cl (aq)

Mg(OH)2 (s) + 2NaCl (aq)2

Note that precipitation reactions involve an ion-exchange process without changes in oxidation state of any species

(i)

(ii)

(iii)

(A) i (D) i and ii

(B) ii (E) ii and iii

(C) iii

Take Home ProblemTake Home Problem

25

Reduction-Oxidation Reactions (Redox)

• A redox reaction can be identified by changes in oxidation numbers (O.N.) in the reactants and products

• The reducing agent loses electrons and is oxidized• The oxidizing agent gains electrons and is reduced

Example (Lab 2):

Zn(s) + 2 HCl(aq) → H2(g) + ZnCl2(aq)

Zn(s) is oxidized (loses 2 e)

H+(aq) is reduced (each H+ gains 1 e)

Zn is the reducing agent

H+ is the oxidizing agent

O.N. 0 +1 -1 0 +2 -1

LEO says GER or OIL RIG

p. 165-177 (153-163, 9th ed.)

26

Concept Check: Oxidation States of Nitrogen

N Biogeochemical Cycle

Fig. 5-15, p. 176 (5-9, p 162, 9th ed.)

27

iClicker Question #6iClicker Question #6

What is the oxidation number for phosphorous in Na2HPO4?

a. 0b. +3c. -2d. +5

28

Redox Reactions

Thermite Reaction (or Goldschmidt reaction, 1893) A classic redox reaction involving hematite (rust) and aluminum for welding applications/pyrotechnics

http://www.youtube.com/watch?v=Yex063_Fblk

°H < 0; T > 2,000 K

Fe2O3 (s) + 2Al (s) 2Fe (l) + Al2O3 (s)+3 00 +3

Oxidizing agent

Reducing agent

Highly Exothermic!Consider Half-Reactions

1. Fe3+ (s) + 3e- Fe (l) Reduction (Gains e)

2. Al (s) Al3+ (s) + 3e- Oxidation (Loses e)

A redox reaction is an electron transfer process!http://en.wikipedia.org/wiki/Thermite

29

iClicker Question #7iClicker Question #7

Identify the oxidizing agent in the following redox reaction:K2Cr2O7 (aq) + HI (aq) --> KI (aq) + CrI3 (aq) + I2 (s) + H2O (l)

a. Ib. Cr2O7

2-

c. K+

d. Cr3+

e. H2O

30

Steel and related iron-based alloys are widely used in construction

Smelting of iron ore in a blast furnace Chemical reduction method for iron (Fe) extraction; Feedstocks: C, Fe2O3, CaCO3

From the Iron Age to Post-Modern Age

Reduction of Iron Oxide

Fe2O3 (s) Fe (l)

+3 0+2 +4

0C (s) + ½ O2 (g)

H° < 0Purify /Alloy

Fe2O3 (s) + 3 CO (g) Fe (l) + 3 CO2 (g)

Steel & Steel AlloysSlag

Stainless steel

Fe (Cr, Ni)http://en.wikipedia.org/wiki/Iron_blast_furnace

http://en.wikipedia.org/wiki/Iron_ore

http://en.wikipedia.org/wiki/Stainless_steel

31

Hamilton: Steel CityBlast Furnace: Continuous Generation of Fe (l)

Hot Air Injection

C, Fe2O3, CaCO3

Pig Iron, Fe (l) 3 - 4 % C

Slag (Silicates)

Waste Gases: CO2, CO, SO2, NOx, H2O

Fig 23-9 p. 1044 (Fig 23.8, pg 976, 9th ed.)

Steel: Fe < 1% C

Scrubbing of waste gases needed to reduce emissions

& lower energy costs!

U. S. Steel Canada (Stelco) & ArcelorMittal Dofasco Inc.

32

Balancing Redox Reactions: Half-reactions

p 170-174 (p. 157-161, 9th ed.)

1. Deduce the oxidation numbers for all species This will identify the oxidizing and reducing agents

2. Write reduction and oxidation skeleton half-reactions3. Balance the redox atoms (usually not O, H unless they are participating in the redox chemistry) 4. Add the correct number of electrons to each half-reaction 5a. If acidic conditions: Balance O by adding H2O then H by H+

5b. If basic conditions: Balance as if in acidic conditions, then add OH- to balance the H+ (making water), then cancel the H2O (or balance the negative charges by adding OH-, then balance O & H by adding H2O)6. Check atoms and charges. Multiply half-reactions by a factor, if needed, to make the number of electrons transferred match. 7. Write the net redox reaction!

33

Balancing Redox Reactions: Acidic Conditions

Fe2+ (aq) + MnO4- (aq) Fe3+ (aq) + Mn2+ (aq)

Half-cell Reactions:

Fe2+ (aq) Fe3+ (aq) Oxidation + 1e-

Reduction MnO4- (aq) Mn2+ (aq)+ 5e- + 4H2O (l)

+7+ 8H+ (aq)

Net Balanced Redox Reaction

X 5

5Fe2+ (aq) + MnO4- (aq) + 8H+ (aq)

Balance the following reaction under acidic conditions:

5Fe3+ (aq) + Mn2+ (aq) + 4H2O (l)

p. 171-172 (157-158, 9th ed.)

34

Balancing Redox Reactions: Basic Conditions

SO32 (aq) + MnO4

(aq) SO42 (aq) + MnO2 (s)

Half-cell Reactions:

SO32 (aq) + H2O (l) SO4

2 (aq) Oxidation + 2e

Reduction MnO4 (aq) MnO2 (s)+ 3e + 4H+ (aq)

+7

Net Balanced Redox Reaction

X 3

3SO32 (aq) + 2MnO4

(aq) + H2O (l)

+4 +6

+4X 2

+ 2H+ (aq)

+ 2H2O (l)

Balance the following reaction under basic conditions:

3SO42 (aq) + 2MnO2 (s) + 2OH (aq)

p. 172-174 (158-160, 9th ed.)

3SO32 (aq) + 2MnO4

(aq) + 2H+ (aq) 3SO4

2 (aq) + 2MnO2 (s) + H2O (l)

35

iClicker Question #8iClicker Question #8

When the following is balanced in a basic solution:MnO4

- (aq) + C2O42- (aq) --> MnO2(s) + CO3

2-

The coefficient in front of CO32- is:

a. 1b. 2c. 3d. 4e. 6

36

Disproportionation Reactions

Hydrogen Peroxide (H2O2) Reactive molecule because of weak O-O single bond

One reactant (H2O2) acts as both reducing and oxidizing agent

OH

O

H.... ..

..

2H2O2 (aq) 2H2O (l) + O2 (g)

3% H2O2 as disinfectantH2O2 (aq) O2 (g) + 2e- + 2H+

H° < 0

Half-Reactions

Oxidation-1 0

Reduction H2O2 (aq) + 2e- + 2H+ 2H2O (l) -1 -2

Topical antiseptic as H2O2 can oxidize microbes

2H2O2 (aq) 2H2O (l) + O2 (g)

p. 174 (p. 160, 9th ed.)

37

Observe and predict the outcome of these two reactions

REDOX Chemical Reactions: Demo

Redox Chemical Reactions

CuSO4 (aq) + Zn (s)

AgNO3 (aq) + Cu (s)

1.

2.

Observations…

Cu (s) + Zn2+ (aq)

Ag (s) + Cu2+ (aq)

As in Lab 2

38

A Closer Look…

Cu (s) + Zn2+ (aq)CuSO4 (aq) + Zn (s)

Fig 5-12, p. 167 (Fig 5-7, p. 155)

39

Acid-Base Reactions

• Involve proton (H+) transfer (Bronsted-Lowry definition)

Example:

• The focus of an upcoming section (Ch 16)

HCl(aq) + NaOH(aq) H2O(l) + NaCl(aq) (Lab 1)

Acid Base (OH)

H+ donor H+ acceptor

p. 160-165; 177-181 (p. 149-153, 163-165, 9th ed.)