Redox and Electrode Potentials Word Stimulants

Question 1

Oxidising agent

Answer 1

Takes electrons to atom being oxidised

Contained atom being reduced

Question 2

Reducing agent

Answer 2

Adds electrons to atom being reduced

Contains atom being oxidised

Question 3

Half equations

Answer 3

Number of electrons lost = number of electrons gained

Question 4

Overall redox equation from half equation

Answer 4

Balance by making electrons same on each side
Cancel out electrons and common species
Combine half equations

Question 5

Overall redox equation from oxidation numbers

Answer 5

Increase in oxidation no = decrease in oxidation numbers
Balance oxidation numbers
Balance remaining atoms and cancel out common species

Question 6

Manganate (VII) redox titrations

Answer 6

Reducing agent titred with oxidising agent
Used for analysing reducing agents (reduces MnO4- to Mn2+)
Acidified manganate (VII) = oxidising agent

Question 7

Potassium Manganate (VII)

Answer 7

KMnO4
Added to burette
Reducing agent - pipette - conical flask + dilute H2SO4 (supply H+)
Added to flask : deep purple > colourless
End point : colourless > permanent pink (indicates excess MnO4-)
Self indicating
Replaced with other oxidising agents (H+/Cr2O7^2-)

Question 8

Modifications to other redox reactions

Answer 8

Depend on oxidising agent
Reducing agent being analysed
Colour change

Question 9

Iron (II) Manganate (VII)

Answer 9

Iron compound - reducing agent

Question 10

Iodine/thiosulfate redox reactions

Answer 10

Used to analyse oxidising agents (eg Cu (II) ions)
Oxidising agent (iodide ions oxidised to iodine) + excess iodide ions
2I-(aq) > I2(aq) + 2e-

Question 11

Iodide titrated with S2O3^2-(aq)

Answer 11

Iodine - reduced
S2O3^-2 - oxidised
2S2O3^-2 + I2 > 2I- + S4O6^2-

Question 12

Iodine/thiosulfate redox reaction method

Answer 12

Standard solution of Na2S2O3 added to burette
Oxidising agent pipette to conical flask
Excess KI(aq) added
2I- > I2 + 2e-
Na2S2O3 added from burette > flask
End point approaches : yellow-brown > pale straw colour
+ Starch indicator : pale straw colour > blue/black
End point : Blue/black > colourless (all I2 reacted)

Question 13

Half cell

Answer 13

Contains chemical species present in redox half equation

Question 14

Metal/metal ion half cell

Answer 14

Metal Rod
Solution of metal ion
Zn^2+ + 2e- <=> Zn

Question 15

Ion/ion half cell

Answer 15

Solutions of ions of same element - different oxidation states
Inert platinum electrode
Fe^3+ + e- <=> Fe^2+

Question 16

Electrode potential

Answer 16

Tendency for electrons to be gained and for reduction in half cell