Chimie Redox

Question 1

What is oxidation number?

Answer 1

a no. assigned to an atom in substance to show state of oxidat n

Question 2

Define redox reactions

Answer 2

electron transfer react n where both oxidat n and reduct n occur concurrently

Question 3

Define disproportionation reaction

Answer 3

Redox rxn where same element in same rxt is oxidised and reduced concurrently

Question 4

H2O2 can act as…? Give the equation for the reaction

Answer 4

Both oxidising and reducing agent

oxidise: H2O2 ->O2
reduce: H2O2 -> H2O

Question 5

How to determine relative strengths of oxidising and reducing agents?

Answer 5

If both substance A and B are oxidising/reducing agents, and A oxidises/reduces B, A is a stronger oxidising/reducing agent than B

Question 6

What is the pneumonic for constructing half equations?

Answer 6

For acidic mediums,
Apple Of His Eye (AOHE)
For basic mediums, add OH- to both sides of eq n to neutralise H+ ions

(ensure to simplify the eq n)

Question 7

What must you do when constructing full redox eq n using half eq n?

Answer 7

No. of electrons lost = no. of electrons gained

Question 8

I2 + 2S2O3²- –> ?
What is the colour change?

Answer 8

I2 + 2S2O3-² –> S4O6²- + 2I-

Brown to yellow to colourless
(when starch is added when yellow, turns blue-black, then colourless)

Question 9

How to determine NEW Oxidation Number from data? (Hint: What r the steps?)

Answer 9

Step 1:
Establish mole ratio btw 2 rxts (eg nA=mB)
Step 2:
Establish mole ratio btw no of electrons transferred and known rxt using half eq n (eg nA=pe-)
Step 3:
Combine mole ratio in steps 1 and 2 (eg nA=mB=pe-)
Step 4:
Determine amt of electrons transferred/mol of unknown rxt (eg B=p/m e-
Step 5:
This no of moles of electrons gained or lost can then be used to find og or final oxidation number (eg new oxidation number = +3+(-2) = +1)