[4.3] redox

Question 1

what is a redox reaction?

Answer 1

a reaction involving both reduction and oxidation processes

Question 2

what are roman numerals used to indicate?

Answer 2

the oxidation number of an atom that can exist in more than one oxidation state

• names with roman numbers are called systematic names eg. iron (iii) oxide

Question 3

which one of the two atoms carries the negative oxidation number?

Answer 3

the more electronegative one

Question 4

how can oxidation be described? [4]

Answer 4

• addition of oxygen
• loss of hydrogen
• loss of electrons
• increase in oxidation number

Question 5

how can reduction be described? [4]

Answer 5

• loss of oxygen
• addition of hydrogen
• gain of electrons
• decrease in oxidation number

Question 6

what is an oxidising agent? [3]

Answer 6

• oxide other species
• accept electrons
• are themselves reduced

Question 7

what is a reducing agent? [3]

Answer 7

• reduce other species
• donate electrons
• are themselves oxidised

Question 8

how do you write half equations?

Answer 8

break things down into charges

• CuO + Mg -> MgO + Cu
• (Cu²⁺ + O²⁻) + Mg -> (Mg²⁺ + O²⁻) + Cu
• Mg -> Mg²⁺ + 2e⁻ (oxidation)
• Cu²⁺ + 2e⁻ -> Cu (reduction)

Question 9

how do you write a redox equation from a half equation?

Answer 9

1. balance the electrons (eg. x2 on one equation, x3 on the other)
2. add and cancel electrons after putting the two equations together
3. cancel any species that are on both sides of the equation

Question 10

how do you balance a redox equation using the oxidation number?

Answer 10

1. write an equation using the information provided
2. assign oxidation numbers to identify the atoms that change their oxidation number
3. balance only the species that contain the elements that have changed their oxidation number (balance number of electrons)
4. balance any remaining atoms