Chapter 6. Electrochemistry

Question 1

What is a redox reaction?

Answer 1

A redox reaction is one where reduction and oxidation have taken place together

Question 2

Define oxidation

Answer 2

1. The loss of electrons i.e e.g. Zn –> Zn²⁺ + 2e^-
2. The increase in oxidation number

Question 3

The oxidation number rules

Answer 3

1. the oxidation number of any uncombined element is zero i.e Zn Na O₂
2. In compounds many atoms or ions have fixed oxidation numbers
   -Group 1 - +1
   -Group 2 - +2
   -Fluorine - -1
   -Hydrogen - +1 (except in metal hydrides such as NaH where it is -1)
   -Oxygen is -2(except in peroxides where it is -1 and F²0 where it is +2)
   -Aluminium - +3
   -Chlorine - -1(except in compounds with F and O where it is positive)
3. In a monoatomic ion the oxidation number of an element is always the same as the charge like Cl^-
4. Sum of oxidation numbers in a compound must add up to zero
5. Sum of oxidation numbers in an ion is equal to the charge on that ion6. In either a compound or an ion, the more electronegative element is given the negative oxidation number

Question 4

Note

Answer 4

Make sure you know how to balance equations using oxidation numbers. In dispropotionation reactions aswell

Question 5

Note

Answer 5

Make sure you know how to write half equations and ionic equations

Question 6

What are oxidising and reducing agents

Answer 6

oxidising agents are electron acceptors and reducing agents are electron donors

Question 7

Colours of copper oxides

Answer 7

Copper 2 - black
Copper 1 - red

Question 8

What is a dispropotionation reaction?

Answer 8

A reaction in which the same elementis both reduced and oxidised