Redox and electrode potentials

Question 1

What is oxidation?

Answer 1

Loss of electrons
Increase in oxidation no
Gain of oxygen
Loss of hydrogen

Question 2

What is reduction?

Answer 2

Gain of electrons
Decrease in oxidation no
Loss of oxygen
Gain of hydrogen

Question 3

Oxidation energy rules

Answer 3

Uncombined element, 0
Combined hydrogen, 1+
Combined oxygen, 2-
Ion of element, ionic charge

Question 4

Oxidising agents and reducing agents

Answer 4

Remove electrons from species being oxidized, reduced itself and vice versa

Question 5

Construction of redox equations with half equations

Answer 5

Write reduction, oxidation half equations.
Balance electrons so both equations have the same no
Add equations together, balance remaining atoms

Question 6

Construction of redox equations using oxidation nos

Answer 6

Assign oxidation nos to identify atoms that change oxidation nos
Only balance species that maintain elements that have changed oxidation no (+6 -6)
Add 2 equations together and balance any remaining atoms

Question 7

Predicting products of redox reactions

Answer 7

Water often forms during aq redox

H+, OH- can be formed too

Question 8

Writing half equations

Answer 8

Use info given
Assign oxidation nos
Balance electrons
Balance remaining atoms, predict further products

Question 9

Manganate(VII) titration reduction equation

Answer 9

MnO4-(aq) + 8H+(aq) + 5e- => Mn2+(aq) + 4H2O(l)

Question 10

Manganate(VII) titration

oxidation equation

Answer 10

Fe2+(aq) => Fe3+(aq) + e-

Question 11

Overall manganate(VII) titration equation

Answer 11

MnO4-(aq) + 8H+(aq) + 5Fe2+(aq) => Mn2+(aq) + 5Fe3+(aq) + 4H2O(l)

Question 12

Manganate(VII) titration method

Answer 12

MnO4- ions are reduced, reducing agent must be oxidized
Standard solution of KMnO4, is added to the burette
Using a pipette, add a measured volume of solution being analyzed to conical flask
Add excess of dilute sulphuric acid as a source of H+
This is a self indicating reaction
During the titration, Mn(VII) reacts and decolourises as it is being added, indicates an excess of MnO4- ions
When the pink color remains for 10 seconds, the end point has just been reached
Repeat until 2 concordant tires have been obtained