redox reaction1 analytical chemistry chem. 243 redox titration chapter 6
TRANSCRIPT
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.
Oxidation-Reduction Reactions
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
Oxidation-Reduction Reactions
Redox reaction7 Redox reaction7
LEOLEO the lion says the lion says GERGER!!oossee
lleeccttrroonnss
xxiiddaattiioonn
aaiinn
lleeccttrroonnss
eedduuccttiioonn
GER!GER!
Oxidation-Reduction Reactions
Na Na+ + e- Cl + e- Cl -
Negative charge represents electron richness
Positive charge represents electron deficiency
Redox reaction8 Redox reaction8
Oxidation-Reduction Reactions
(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
Redox reaction9 Redox reaction9
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-
Redox reaction10 Redox reaction10
Redox reaction11 Redox reaction11
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-
Oxidation-Reduction Reactions
Redox reaction12 Redox reaction12
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
Oxidation-Reduction Reactions
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
Redox reaction14 Redox reaction14
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.
Redox reaction15 Redox reaction15
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
Redox reaction19 Redox reaction19
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
Redox reaction20 Redox reaction20
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
Redox reaction21 Redox reaction21
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
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 Mg in MgCl2?
+225 Redox reaction
Redox reaction26
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 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
chemical reaction in aqueous solution
29
Combination Reaction
A + B C
2Al + 3Br2 2AlBr3
0 0 +3 -1
Types of Oxidation-Reduction Reactions
More than one reactant, single product
+2 +1
chemical reaction in aqueous solution
30
Types of Oxidation-Reduction Reactions
2KClO3 2KCl + 3O2
C A + B
+1 +5 -2 +1-1 0
Decomposition Reaction
Single reactant, more than one product
chemical reaction in aqueous solution
31
Displacement Reaction
A + BC AC + B
Cl2 + 2KBr 2KCl + Br2
Halogen Displacement0 +1 0 -1
-10 -1 0
Halogen Displacement
Types of Oxidation-Reduction Reactions
One element displaces another from a compound
chemical reaction in aqueous solution
32
Displacement Reaction
A + BC AC + B
TiCl4 + 2Mg Ti + 2MgCl2
Metal Displacement
4.4
0 +2 0 +2
0+4 0 +2
Metal Displacement
Types of Oxidation-Reduction Reactions
chemical reaction in aqueous solution
33
Displacement Reaction
A + BC AC + B
Sr + 2H2O Sr(OH)2 + H2 Hydrogen Displacement
Types of Oxidation-Reduction Reactions
0 +1 +2 0
+10 0 +3
Hydrogen Displacement
chemical reaction in aqueous solution
34
Displacement Reaction
A + BC AC + B
TiCl4 + 2Mg Ti + 2MgCl2
Metal Displacement
4.4
0 +2 0 +2
0+4 0 +2
Metal Displacement
Types of Oxidation-Reduction Reactions
Redox reaction35 Redox reaction35
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!