Redox reaction1 ANALYTICAL CHEMISTRY Chem. 243 Redox titration Chapter 6.

Redox reaction1

ANALYTICAL CHEMISTRY

Chem. 243

Redox titration

Chapter 6

Redox reaction2

Quantitative Volumetric AnalysisLast measurement is volume

Neutralization titrations

Oxidation titrations

Precipitation titrations

Complexometric

titrations.

Redox reaction3

This lecture covers three topics:• Redox Titrations.• Assignment of oxidation numbers

• Balancing of redox equations

Redox reaction4

Redox Reactions.

Oxidation

Reduction

Oxidation-Reduction Reactions

Redox reaction5

Oxidation and reduction go hand in hand. In a reaction, if there is an atom undergoingoxidation, there is probably another atom undergoing reduction.

When there is an atom that donates electrons, there is always an atom that accepts electrons.

Electron transfer happens from one atom toanother.


Redox reaction6 Redox reaction6

Oxidation:•Gain of oxygen

•Loss of electrons

Reduction:•Loss of oxygen

•Gain of electrons

Increase in oxidation

number

Decrease in oxidation

number



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lleeccttrroonnss

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lleeccttrroonnss

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GER!GER!


Na Na+ + e- Cl + e- Cl -

Negative charge represents electron richness

Positive charge represents electron deficiency



(electron transfer reactions)

2Mg 2Mg2+ + 4e-

O2 + 4e- 2O2-

Oxidation half-reaction (lose e-)

Reduction half-reaction (gain e-)

2Mg + O2 + 4e- 2Mg2+ + 2O2- + 4e-

2Mg + O2 2MgO


2Mg(s) + O2(g) 2MgO(s)

Oxidised – gains oxygen

Must be a redox!

Mg Mg2+

O O2-

Put the e- in.

+2e-

+2e-

Oxidised – loss of e-

Reduced – gain of e-



Cu(s) + 2AgNO3(aq) Cu(NO3 )2(aq) + 2Ag(s)

2Ag+ 2Ag

Cu Cu2+

Complete the half-equations

+2e-

+2e-

Oxidised?Reduced?

Oxidised – loss of e-

Reduced – gain of e-



Zn (s) + CuSO4 (aq) ZnSO4 (aq) + Cu (s)Zn is oxidizedZn Zn2+ + 2e-

Cu2+ is reducedCu2+ + 2e- Cu

Zn is the reducing agent

Cu2+ is the oxidizing agent

4.4

Copper wire reacts with silver nitrate to form silver metal.What is the oxidizing agent in the reaction?

Cu (s) + 2AgNO3 (aq) Cu(NO3)2 (aq) + 2Ag (s)

Cu Cu2+ + 2e-

Ag+ + 1e- Ag Ag+ is reduced Ag+ is the oxidizing agent


Cu is the reducing agentCu is oxidized

Redox reaction13

Nuggets of redox processes

Where there is oxidation there is always reduction

Oxidizing agentReducing agent

Is itself reducedIs itself oxidized

Gains electronsLoses electrons

Causes oxidationCauses reduction


Oxidation number

The charge the atom would have in a molecule (or anionic compound) if electrons were completely transferred.

1. Free elements (uncombined state) 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 = -2

3. The oxidation number of oxygen is usually –2. In H2O2

and O22- it is –1.


H2(g) + ½ O2(g) H2O(g)+10

-20O

H

Oxidised?

H – increase in oxidation

number

Reduced?

O – decrease in oxidation

number

Oxidation number

Redox reaction16

Oxidation number

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

Redox reaction17

ns1

ns2

ns2

np1

ns2

np2

ns2

np3

ns2

np4

ns2

np5

ns2

np6

d1

d5 d10

4f

5f

Ground State Electron Configurations of the Elements

Redox reaction18

+1

+2

+3 -1-2-3

Cations and Anions Of Representative Elements


5. 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.

HCO3-

O = -2 H = +1

3x(-2) + 1 + ? = -1

C = +4

Oxidation numbers of all the elements in HCO3

- ?

6. Oxidation numbers do not have to be integers. Oxidation number of oxygen in the superoxide ion, O2

-, is -½.

Oxidation number


NaIO3

Na = +1 O = -2

3x(-2) + 1 + ? = 0

I = +5

H = +1

2x(+1) + ? = 0

O2 = -2

K2Cr2O7

O = -2 K = +1

7x(-2) + 2x(+1) + 2x(?) = 0

Cr = +6

Oxidation numbers of all the elements in the following ?

Oxidation number

H2O2


H2C2O4

H = +1 O = -2

1(2) +? +4x(-2) = 0

2C = +6

IF7

F = -1

7x(-1) + ? = 0

I = +7

K MnO4

O = -2 K = +1

4x(-2) + 1x(+1) + (?) = 0

Mn = +7

Oxidation numbers of all the elements in the following ?

Oxidation number

(-8) + (+1) + (?) = 0

Chromium gives great example of different oxidation numbers

Different oxidation states of chromium have different colors

Chromium (II) chloride = blue

Chromium (III) chloride = green

Potassium chromate = yellow

Potassium dichromate = orange

Redox reaction24

Oxidation NumbersOxidation Numbers

•The oxidation numbers of atoms in a compound add

up to zero .

F-1

O-2

H+1

Cl-1

Oxidation state of C in CO2?

? – 4 = 0

? = +4Put the +!

24 Redox reaction

Redox reaction25



up to zero .

F-1

O-2

H+1

Cl-1

Oxidation state of Mg in MgCl2?

+225 Redox reaction

Redox reaction26



up to zero .

F-1

O-2

H+1

Cl-1

Oxidation state of N in NH3?

-326 Redox reaction

Redox reaction27

Oxidation NumbersOxidation Numbers•The oxidation

numbers of atoms in an ion add up to the

charge on the ion .

F-1

O-2

H+1

Cl-1

Oxidation state of S in S2-?

-227 Redox reaction

chemical reaction in aqueous solution

28

Types of Oxidation-Reduction Reactions

Oxidation Reduction Reaction

Combination

Reaction Decomposition

Reaction

DisplacementReaction


29

Combination Reaction

A + B C

2Al + 3Br2 2AlBr3

0 0 +3 -1


More than one reactant, single product

+2 +1


30


2KClO3 2KCl + 3O2

C A + B

+1 +5 -2 +1-1 0

Decomposition Reaction

Single reactant, more than one product


31

Displacement Reaction

A + BC AC + B

Cl2 + 2KBr 2KCl + Br2

Halogen Displacement0 +1 0 -1

-10 -1 0

Halogen Displacement


One element displaces another from a compound


32


A + BC AC + B

TiCl4 + 2Mg Ti + 2MgCl2

Metal Displacement

4.4

0 +2 0 +2

0+4 0 +2

Metal Displacement



33


A + BC AC + B

Sr + 2H2O Sr(OH)2 + H2 Hydrogen Displacement


0 +1 +2 0

+10 0 +3

Hydrogen Displacement


34


A + BC AC + B

TiCl4 + 2Mg Ti + 2MgCl2

Metal Displacement

4.4

0 +2 0 +2

0+4 0 +2

Metal Displacement



Ca2+ + CO32- CaCO3(s)

NH3 + H+ NH4+

Zn + 2HCl ZnCl2 + H2

Ca + F2 CaF2

Precipitation

Acid-Base

Redox (H2 Displacement)

Redox (Combination)

Classify the following reactions.

Redox reaction36

What is redox titration?A TITRATION WHICH DEALS WITH A REACTION INVOLVING OXIDATION AND REDUCTION OF CERTAIN CHEMICAL SPECIES.

What is a titration?The act of adding standard solution in small quantities to the test solution till the reaction is complete is termed titration.

Redox reaction37

Oxidation NumbersOxidation Numbers•The oxidation

numbers of atoms in an ion add up to the

charge on the ion .

F-1

O-2

H+1

Cl-1

Oxidation state of N in NH4

+?

-337 Redox reaction

Redox reaction38

Problem 12-5: Redox Titration- I

Volume (L) of KMnO4 Solution

Moles of KMnO4

M (mol/L)

Molar ratioin redox rxn.

Chemical Formulas

Moles of CaC2O4

Problem: Calcium Oxalate was precipitated from 1.00 mL blood by the addition of Sodium Oxalate so the Ca2+ conc. in the blood could be determined. This precipitate wasdissolved in a sulfuric acid solution,which then required 2.05 mL of 4.88 x 10-4 M KMnO4 to reach the endpoint via the rxn. of Fig. 4.14. a) Calculate the moles of Ca2+.b) Calculate the Ca2+ conc. in blood.Plan: a) Calculate the moles ofCa2+ in the H2SO4 solution (and blood sample).b) Convert the Ca2+ conc.into units of mg Ca2+/ 100 mL blood.

Moles of Ca+2

a)

b)

c)

Redox reaction39

Equation:2 KMnO4 (aq) + 5 CaC2O4 (aq) + 8 H2SO4 (aq) 2 MnSO4 (aq) + K2SO4 (aq) + 5 CaSO4 (aq) + 10 CO2 (g) + 8 H2O(l)

Problem 12-5: Redox Titration - Calculation - II

a) Moles of KMnO4

b) Moles of CaC2O4

c) Moles of Ca+2

Redox reaction40

Problem 12-5: Redox Titration - III

Moles of Ca2+/ 1 mL of blood

Moles of Ca2+/ 100 mL blood

Mass (g) of Ca2+/ 100 mL blood

Mass (mg) of Ca2+ / 100 mL blood

multiply by 100 a) Calc of mol Ca2+ per 100 mL

M (g/mol) b) Calc of mass of Ca2+ per 100 mL

1g = 1000mg c) convert g to mg!

Redox reaction41

Titration of Oxalic acid Vs KMnO4

Primary standard

Secondary standard

16 H+(aq) + 2 MnO4-(aq) + 5 C2O4

-2(aq) 2 Mn+2(aq) + 10 CO2(g) + 8 H2O(l)

5 C2O42- ions are oxidized by 2 MnO4

- ions to 10 CO2 molecules. Conversely 2 MnO4

- is reduced by 5 C2O42-

ions to 2Mn2+ ions.

Redox reaction42

Well done!

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Redox reaction1 ANALYTICAL CHEMISTRY Chem. 243 Redox titration Chapter 6.

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