Redox systems

What is oxidation?

Loss of electrons or increase in oxidation number or gain of O2 / loss of H

What is an oxidising agent?

the species that is reduced in a reaction and causes another species to be oxidised so accepts electrons

What is reduction?

gaining of electrons or decrease in oxidation number or loss of O2 / Gain of H

What is a reducing agent?

the species that is oxidised in a reaction and causes another species to be reduced so donates electrons

How do you form the overall redox equation?

1. Identify the separate half equations (If the O is unequal add H2O, if H is unequal add H+, then if the charge isn’t equal add e-s)

2. Balance the electrons so both half equations have same number

3. Add half equations together

4. Cancel out electrons and other compounds that are equal

What is acidified dichromate ions (Cr₂O₇^2-) reduced to in a redox reaction?

2Cr³⁺

What is the colour change when Cr₂O₇^2- is reduced to 2Cr³⁺?

Orange → green

What is acidifed mangnate ions (MnO₄^-) reduced to in a redox reaction?

Mn²⁺

What is the colour change when MnO₄^- is reduced to Mn²⁺?

Purple → colourless

What do redox titrations determine?

the amounts of species being oxidised or reduced

Why don’t redox titrations need an indicator?

redox titrations involve a species that self-indicates so change colour between oxidation states

Half equation for reduction of I₂ and colour change:

I₂ (blue / black)→ 2I^- (blue / black DISAPPEARS) + 2e^-

What needs to be present so I₂ can be reduced?

S₂O₃^2- ions

What is thiosulfate ions (S₂O₃^2-) reduced to?

S₄O₆^2-

What is iodate ions (IO₃^- ) oxidised to and colour of product?

3I₂ (red / brown solution)

What does iodate ions need to be added to in order to be oxidised?

I^- ions