4-1Yellow Stone National Park, Jon Sullivan, June, 2003

(c) 문화재청

The Major Classes of Reactions

Chapter 4

4-2

수용액에서의 반응

1. 수용액의 일반적 성질- 전해질과 비전해질

2. 침전반응- 이온 방정식 , 용해도 규칙

3. 산 - 염기 반응4. 산화 - 환원 반응 - 산화수5. 용액의 농도6. 용액의 화학양론 - 적정

4-3

The Major Classes of Chemical Reactions

4.6 Elements in Redox Reactions

4.1 The Role of Water as a Solvent

4.2 Writing Equations for Aqueous Ionic Reactions

4.3 Precipitation Reactions

4.4 Acid-Base Reactions

4.5 Oxidation-Reduction (Redox) Reactions

4-4

Charge distribution in H2 and H2O and Molecular Dipole

4-5

Hydration is the process in which an ion is surrounded by water molecules arranged in a specific manner.

4.1

4-6

Hydration of Ions  (i) Hydration represents for the dissolution of a substance in water to get adsorb water molecule. Hydration of ions is the exothermic process. 

M(g)+ + Aq → M+(aq); ΔH = –Hydration Energy.  (ii) Smaller the cation, greater is the degree of hydration. Hydration energy is in the order of, Li+ > Na+ > K+ > Rb+ > Cs+

 (iii) Li+ being smallest in size has maximum degree of hydration, moves very slowly under the influence of electric field and, therefore, is the poorest conductor current among alkali metals ions.          Relative ionic radii    Cs+ > Rb+ > K+ > Na+ > Li+           Relative hydrated ionic radii  Li+ > Na+ > K+ > Rb+ > Cs+

          Relative conducting power Cs+ > Rb+ > K+ > Na + > Li+

4-7

Enthalpy of Hydration (ΔHhyd kJ/mol) of Some Typical Ions

Ion ΔHhyd Ion ΔHhyd  Ion ΔHhyd

H+ -1130 Al3+ -4665 Fe3+ -4430　 　 　 　 　

Li+ -520 Be2+ -2494 F- -505Na+ -406 Mg2+ -1921 Cl- -363K+ -322 Ca2+ -1577 Br- -336Rb+ -297 Sr2+ -1443 I- -295Cs+ -276 Ba2+ -1305 ClO4

- -238　 　 　 　 　

Cr2+ -1904 Mn2+ -1841 Fe2+ -1946Co2+ -1996 Ni2+ -2105 Cu2+ -2100Zn2+ -2046 Cd2+ -1807 Hg2+ -1824

4-8

An electrolyte is a substance that, when dissolved in water, results in a solution that can conduct electricity.

nonelectrolytesolution

electrolytesolution

sugar solution NaCl solution

4-9

Determining Moles of Ions in Aqueous Ionic Solutions

How many moles of each ion are in the following solutions?

(a) 5.0 mol of ammonium sulfate dissolved in water

(b) 78.5 g of cesium bromide dissolved in water

SOLUTION:

nNH4+ = 5.0 mol ×2/1 = 10. mol

(a) (NH4)2SO4(s) → 2NH4+(aq) + SO4

2-(aq)

H2O

nSO42- = 5.0 mol ×1/1 = 5.0 mol

nCsBr = 78.5 g CsBr /(212.8 g /mol) = 0.369 mol = n Cs+ = nBr- (b) CsBr(s) → Cs+(aq) + Br-(aq)

H2O

4-10

Determining Moles of Ions in Aqueous Ionic Solutions

nCu(NO3)2 = 7.42×1022 formula units /(6.022×1023/mol)= 0.123 mol

nCu2+ = nCu(NO3)2 = 0.123 mol

(c) Cu(NO3)2(s) → Cu2+(aq) + 2NO3-(aq)

H2O

(d) ZnCl2(aq) → Zn2+(aq) + 2Cl-(aq) H2O

nNO3- = 2×nCu(NO3)2 = 0.246 mol

How many moles of each ion are in the following solutions?

(c) 7.42×1022 formula units of copper(II) nitrate dissolved in water(d) 35 mL of 0.84 M zinc chloride

SOLUTION:

nZnCl2 = 35 mL× (L/103mL) ×(0.84 mol/L)= 2.9×10-2 mol

nZn2+ = nZnCl2 = 2.9×10-2 mol nCl- = 2×nZnCl2 = 5.8×10-2 mol

4-11

Determining the Molarity of H+ Ions in Aqueous Solutions of Acids

Nitric acid is a major chemical in the fertilizer and explosives industries. In aqueous solution, each molecule dissociates and the H becomes a solvated H+ ion. What is the molarity of H+(aq) in 1.4M nitric acid?

SOLUTION: One mole of H+(aq) is released per mole of nitric acid (HNO3)

HNO3(l) → H+(aq) + NO3-(aq)

H2O

nH+ = nHNO3 , so MH+ = MHNO3 = 1.4M

4-12

Writing Equations for Aqueous Ionic Reactions

The molecular equationshows all of the reactants and products as intact, undissociated compounds.

The total ionic equationshows all of the soluble ionic substances dissociated into ions.

The net ionic equation

eliminates the spectator ions and shows the actual chemical change taking place.

4-13

Precipitation Reactions

Precipitate – insoluble solid that separates from solution

molecular equation

ionic equation

Na+(aq) and NO3-(aq)

spectator ions

PbI2

precipitate

4.2

2Na+(aq) + 2I-(aq) + Pb2+(aq) + 2NO3-(aq) →PbI2(s) + 2Na+(aq) + 2NO3

-(aq)

2NaI(aq) + Pb(NO3)2 (aq) → PbI2(s) + 2NaNO3(aq)

net ionic equationPb2+(aq) + 2I-(aq) → PbI2(s)

The reaction of Pb(NO3)2 and NaI.

double displacement reaction (metathesis)

2NaI(aq) + Pb(NO3)2(aq) → PbI2(s) + 2NaNO3(aq)

4-14

Predicting Whether a Precipitate Will Form

1. Note the ions present in the reactants.

2. Consider the possible cation-anion combinations.

3. Decide whether any of the ion combinations is insoluble.

solubility rules is very useful tool.

4-15

Cation Na+ K+ NH4

+ Al3

+Mg2

+ Ca2+ Sr2+ Ba2+ Cr3

+Fe3

+Fe2

+ Co2+Ni2+Cu2+ Zn2+ Cd2+ Hg2+ Hg22

+ Ag+ Pb2+ As3+ Sb3+ Bi3+

CH3-COO- S S S S S S S S S U S S S S S S S I I S U U I

Br- S S S S S S S S S S S S S S S S I Ia Ib I D D DCl- S S S S S S S S S S S S S S S S S Ib Ib I D S DI- S S S S S S S S I U S S S U S S Ia Ia I Ia S D I

ClO3- S S S S S S S S U U U S S S S S S S S S U U U

NO3- S S S S S S S S S S S S S S S S S D S S U U D

SO42- S S S S S Ia I Ib S S S S S S S S D I I I U D D

SO32- S S S U S I I I I U I I I U I I U U I I U U U

CrO42- S S S U S S Ia Ia U S I I U S Ia I Ia Ia Ia Ia U U U

C2O42- S S S I I I I I S S I I I I I I I I I I U I D

PO43- S S S Ia Ia Ia Ia Ia I Ia Ia I I Ia Ia I U U Ia Ia U U I

CO32- S S S U Ia I Ia I U U I I I I Ia I I Ia Ia Ia U U U

SiO32- S S U I Ia Ia Ia S U U I I U U Ia I U U U Ia U U I

O2- D D U Ib Ia I I S I Ia Ia I I Ia I I I Ia I I I I IOH- S S U Ia Ia Ia I S I Ia Ia I I Ia Ia I U U U Ia U U DS2- S S S D D Ia I D I I Ia I I Ia Ia I I I Ia Ia I D I

Ia Soluble in AcidsIb Slightly Soluble in Acids

S S=SolubleI I=Insoluble

D=Decomposes in waterU=Compound does not exist or is unsta-ble

4-16

Solubility Rules for Common Ionic Compounds in Water at 25 oC

Soluble Compounds ExceptionAlkali metal(1A) & Ammo-nium(NH4

+)

NO3-, HCO3

-, ClO3-, CH3COO-

Halides(Cl-, Br-, I-) w/ Ag+, Hg22+, Pb2+,

Sulfates(SO42-) w/ Ag+, Ca2+, Sr2+, Ba2+, Hg2

2+, Pb2+,

Insoluble Compounds Exceptions

CO32-, PO4

3-, CrO42-, S2- Alkali metal(1A) compounds, Ammonium

compounds

OH- Alkali metal(1A) compounds, Ba2+,

4-17

Predicting Whether a Precipitation Reaction Occurs; Writing Ionic Equations

Predict whether a reaction occurs when each of the following pairs of solutions are mixed. If a reaction does occur, write balanced molecular, total ionic, and net ionic equations, and identify the spectator ions.

(a) sodium sulfate(aq) + strontium nitrate(aq)(b) ammonium perchlorate(aq) + sodium bromide(aq)

SOLUTION:

(a) Na2SO4(aq) + Sr(NO3)2 (aq) → 2NaNO3(aq) + SrSO4(s)

2Na+(aq) +SO42-(aq)+ Sr2+(aq)+2NO3

-(aq) →

2Na+(aq) +2NO3-(aq)+ SrSO4(s)

Sr2+(aq) + SO42-(aq) → SrSO4(s)

(b) NH4ClO4(aq) + NaBr (aq) → NH4Br (aq) + NaClO4(aq)

All reactants and products are soluble so no reaction occurs.

4-18

Common Acids and BasesAcidsStrong

hydrochloric acid, HCl

hydrobromic acid, HBrhydroiodic acid, HI

nitric acid, HNO3

sulfuric acid, H2SO4

perchloric acid, HClO4

Weakhydrofluoric acid, HF

phosphoric acid, H3PO4

acetic acid, CH3COOH

BasesStrong

Weak

sodium hydroxide, NaOH

calcium hydroxide, Ca(OH)2

potassium hydroxide, KOH

strontium hydroxide, Sr(OH)2

barium hydroxide, Ba(OH)2

ammonia, NH3

salicylic acid, C6H4(OH)COOHascorbic acid(Vitamin C), C6H8O6

4-19

Acid-Base Reactions

HCl(g) + H2O(l) → H3O+(aq) + Cl–(aq)

[H3O+(aq) + Cl–(aq)] + [Na+ (aq) + OH–(aq)] → H2O(l) + Cl–(aq) + Na+(aq) + HOH

When HCl gas dissolves in water,

H+ transfer

HCl(aq) + NaOH(aq),

H+ transfer

H3O+(aq) + OH–(aq)] → H2O(l)

H+ transfer

Johannes Brønsted & Thomas Lowry : acid: proton donor, base: acceptor

4-20

Sr2+(aq) + 2OH-(aq)+ 2H+(aq) + 2ClO4-(aq)

2H2O(l)+Sr2+(aq)+2ClO4-(aq)

Ba2+(aq) + 2OH-(aq) + 2H+(aq) + SO42-(aq)

2H2O(l) + Ba2+(aq) + SO42-(aq)

Writing Ionic Equations for Acid-Base Reactions

Write balanced molecular, total ionic, and net ionic equations for each of the following acid-base reactions and identify the spectator ions.

SOLUTION:(a) Sr(OH)2(aq)+2HClO4(aq) → 2H2O(l)+Sr(ClO4)2(aq)

2OH-(aq)+ 2H+(aq) → 2H2O(l)

(a) strontium hydroxide(aq) + perchloric acid(aq) →

(b) barium hydroxide(aq) + sulfuric acid(aq) →

(b) Ba(OH)2(aq) + H2SO4(aq) → 2H2O(l) + BaSO4(aq)

2OH-(aq)+ 2H+(aq) → 2H2O(l)

4-21

H+(aq) + OH-(aq) → H2O(l)

An acid-base titrationIn a titration a solution of accurately known concentration is added gradually added to another solution of unknown concentration until the chemical reaction between the two solutions is complete.

Equivalence point – the point at which the reaction is complete

Indicator – substance that changes color at (or near) the equivalence point End point – the point at which the indicator changes

4-22

Finding the Concentration of Acid from an Acid-Base Titration

You perform an acid-base titration to standardize an HCl solution by placing 50.00 mL of HCl in a flask with a few drops of indicator solution. You put 0.1524 M NaOH into the buret, and the initial reading is 0.55 mL. At the end point, the buret reading is 33.87 mL. What is the concentration of the HCl solution?

SOLUTION:NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

(33.87-0.55) mL×(L/103 mL) = 0.03332 L

0.03332 L × 0.1524 M= 5.078×10-3 mol

5.078×10-3 mol HCl/0.05000L = 0.1016 M HCl

At the equivalent point, nNaOH = nHCl

nNaOH

MHCl = nHCl/VHCl

4-23

Oxidation number( 산화수 )

1. Free elements have an oxidation number of zero.

Na, Be, K, Pb, H2, O2, P4, ... = 0

2. In monatomic ions, the oxidation number is equal to the charge on the ion.

Li+, Li = +1; Fe3+, Fe = +3; O2-, O = -23. The oxidation number of oxygen is usually –2. In H2O2

and O22- it is –1.

The charge the atom would have in a molecule (or an ionic compound) if electrons were completely transferred to more electronegative atoms.

The sum of the oxidation numbers of all the atoms in a molecule or ion is equal to the charge on the molecule or ion

4-24

4. The oxidation number of hydrogen is +1 except when it is bonded to metals in binary compounds. In these cases, its oxidation number is –1.

5. Group IA metals are +1, IIA metals are +2 and fluorine is always –1.

HSO4-

O = -2 H = +1

4×(-2) + 1 + ? = -1

S = +6

Oxidation numbers of all the elements in HSO4

- ?

4-25

Determining the Oxidation Number of an Element

Determine the oxidation number (O.N.) of each element in these compounds:

(a) zinc chloride (b) sulfur trioxide (c) nitric acid

SOLUTION:

(a) ZnCl2. The O.N. for zinc is +2 and that for chloride is -1.

(b) SO3. Each oxygen is an oxide with an O.N. of -2. Therefore the O.N. of sulfur must be +6.

(c) HNO3. H has an O.N. of +1 and each oxygen is -2. Therefore the N must have an O.N. of +5.

4-26

oxidation states of the main group elements

1

−1

H

1

2

He

3

−1

Li

1

4

Be

2

5

B

1

2

3

6

−4

−3

−2

−1

C

1

2

3

4

7

−3

−2

−1

N

1

2

3

4

5

8

−2

−1

O

1

2

9

−1

F

10

Ne

11

−1

Na

1

12

Mg

1

2

13

Al

1

3

14

−4

−3

−2

−1

Si

1

2

3

4

15

−3

−2

−1

P

1

2

3

4

5

16

−2

−1

S

1

2

3

4

5

6

17

−1

Cl

1

2

3

4

5

6

7

18

Ar

19

K

1

20

Ca

2

31

Ga

1

2

3

32

−4

Ge

1

2

3

4

33

−3

As

2

3

5

34

−2

Se

2

4

6

35

−1

Br

1

3

4

5

7

36

Kr

2

37

Rb

1

38

Sr

2

49

In

1

2

3

50

−4

Sn

2

4

51

−3

Sb

3

5

52

−2

Te

2

4

5

6

53

−1

I

1

3

5

7

54

Xe

2

4

6

8

55

Cs

1

56

Ba

2

81

Tl

1

3

82

−4

Pb

2

4

83

−3

Bi

3

5

84

−2

Po

2

4

6

85

−1

At

1

3

5

7

86

Rn

2

87

Fr

1

88

Ra

2

4-27

• X gains electron(s)• X is reduced• X is the oxidizing

agent• X decreases its

oxidation number

• M loses electron(s)• M is oxidized• M is the reducing

agent• M increases its

oxidation number

M + X → M+ + e- + X → M+ + X- → MX

Oxidation-Reduction (redox) reactions

M X

4-28

Recognizing Oxidizing and Reducing Agents

Identify the oxidizing agent and reducing agent in each of the following:

(a) 2Al(s) + 3H2SO4(aq) → Al2(SO4)3(aq) + 3H2(g)

(b) PbO(s) + CO(g) → Pb(s) + CO2(g)

(c) 2H2(g) + O2(g) → 2H2O(g)

(a) 2Al(s) + 3H2SO4(aq) → Al2(SO4)3(aq) + 3H2(g)0 0+6+1 -2 +3 +6 -2

SOLUTION:

The O.N. of Al increases; it is oxidized; it is the reducing agent.

The O.N. of H decreases; it is reduced; H2SO4 is the oxidizing agent.

(b) PbO(s) + CO(g) → Pb(s) + CO2(g)+2 -2 +2 -2 0 +4 -2

(c) 2H2(g) + O2(g) → 2H2O(g)0 0 +1 -2

4-29

An active metal displacing hydrogen from water:

Large Sodium Explosion

http://www.youtube.com/watch?v=sNdijknRxfU&feature=related

4-30

Displacing one metal with another.

Fe(s) + CuSO4(aq) → Fe(SO4) (aq) + Cu(s)

Shiny White + Blue → Green Solution + Reddish Brown

4-31

The activity series of the metals.

LiKBaCaNa

can displace Hfrom water

stre

ngth

as

redu

cing

age

nts

H2

MgAlMnAnCrFeCd

can displace Hfrom steam

CoNiSnPb

can displace Hfrom acid

CuHg AgAu

cannot displace H from any source

M + H2O → M(OH)x + H2

0 +1 → +x 0

Oxidation

Reduction

4-32

Types of Oxidation-Reduction Reactions

Combination : A + B → C 2Al + 3Br2 → 2AlBr3

Decomposition : C → A + B 2KClO3 → 2KCl + 3O2

0 0 +3 -1

+1 +5-2 +1 -1 0

Combustion : A + O2 → B S + O2 → SO2

0 0 +4 -22Mg + O2 → 2MgO

0 0 +2 -2

Displacement : A + BC → AC + B

Sr + 2H2O → Sr(OH)2 + H2

TiCl4 + 2Mg → Ti + 2MgCl2

Cl2 + 2KBr → 2KCl + Br2

H Displacement

Metal Displacement

Halogen Displacement

0 +1 +2 0

0+4 0 +2

0 -1 -1 0

4-33

Type of Redox Reaction

Classify each of the following redox reactions as a combination, decomposition, or displacement reaction, write a balanced molecular equation for each, as well as total and net ionic equations for part (c), and identify the oxidizing and reducing agents:

(a) magnesium(s) + nitrogen(g) → magnesium nitride (aq)(b) hydrogen peroxide(l) → water(l) + oxygen gas(c) aluminum(s) + lead(II) nitrate(aq) → aluminum nitrate(aq) + lead(s)

4-34

(a) Combination3

0 0 +2 -3

Mg is the reducing agent; N2 is the oxidizing agent.

(b) Decomposition+1-1 +1-2 0

Mg(s) + N2(g) → Mg3N2 (aq)

2 H2O2(l) → 2 H2O(l) + O2(g)

H2O2 is the oxidizing and reducing agent.

(c) Displacement

Al(s) + Pb(NO3)2(aq) → Al(NO3)3(aq) + Pb(s)0 +2 +5 -2 +3 +5 -2 0

2Al(s) + 3Pb(NO3)2(aq) → 2Al(NO3)3(aq) + 3Pb(s)

Pb(NO3)2 is the oxidizing and Al is the reducing agent.

4-35

Disproportionation Reaction

Cl2 + 2OH- → ClO- + Cl- + H2O

Element is simultaneously oxidized and reduced.

Types of Oxidation-Reduction Reactions

0 +1 -1

4-36

다음에서 각 원소의 산화수를 결정하라 .

(a) 산화 스칸듐 (Sc2O3) (b) 염화 갈륨 (GaCl3) (c) 인산 수소 이온 (d) 삼플루오린화 아이오딘

4-37

다음 각 물질이 물에 잘 녹을 것인지 말하고 , 그 이유를 설명하라 .

(a) 벤젠 (C6H6) (b) 수산화 소듐(c) 에탄올 (CH3CH2OH) (d) 아세트산 포타슘(e) 질산 리튬 (f) 글라이신 (H2NCH2COOH)(g) 펜테인 (h) 에틸렌 글라이콜 (HOCH2CH2OH)