Mr Cole Chemistry

Introduction to Redox Questions

Intro to Redox

Redox Worksheet

Definitions

Define the following terms:
a) Oxidation

The loss of electrons.

b) Reduction

The gain of electrons.

c) Oxidising agent

The substance that gains/accepts electrons from a reducing agent in a redox reaction.

d) Reducing agent

The substance that loses/donates electrons to an oxidising agent in a redox reaction.

Trends & Reactions

Oxygen can react with Period 2 and Period 3 elements. When oxygen reacts with fluorine it forms OF2, and when it reacts with phosphorous it forms P4O10. In each case, state which element is reduced and which is oxidised.
O2 + 2F2 → 2OF2
  • The oxygen is oxidised.
  • The fluorine is reduced.
P4 + 5O2 → P4O10
  • The phosphorous is oxidised.
  • The oxygen is reduced.
State and explain the trend in oxidising power of the halogens as you go down the group.
  • The oxidising power decreases as you go down the group.
  • As you go down the group, the distance between the nucleus and the outer shell electrons increases.
  • The shielding also increases.
  • This reduces the strength of the electrostatic force of attraction between the nucleus and any incoming electrons.
  • This means that they are less good at attracting electrons to their outer shell.
State and explain the trend in oxidising power of Period 2 elements as you go across the period.
  • The oxidising power increases.
  • The number of shells remains the same but the number of protons increases.
  • This results in the same amount of shielding, but a decreased distance between the nuclei and the outer shell.
  • This means that the electrostatic force of attraction increases as you go across the period.
  • This results in an increased ability to attract electrons (oxidising power).

Identifying Redox Reactions

For each of the following reactions, state whether they are a redox reaction and, in the cases that they are, explain why.
a)
H2SO4 + 2NaOH → Na2SO4 + 2H2O
  • No
  • Nothing changes oxidation state (Neutralisation reaction).
b)
MgCl2 + 2Na → 2NaCl + Mg
  • Yes
  • Magnesium is reduced (Mg2+ → Mg0).
  • Sodium is oxidised (Na0 → Na+).
c)
Cl2 + H2O → HCl + HClO
  • Yes
  • Chlorine is oxidised (0 → +1 in HClO).
  • Chlorine is reduced (0 → -1 in HCl).
  • This is a disproportionation reaction.
d)
2MnO4– + 6H+ + 5H2O2 → 2Mn2+ + 8H2O + 5O2
  • Yes
  • Manganese is reduced (Mn+7 in MnO4– → Mn2+).
  • Oxygen is oxidised (O-1 in H2O2 → O0 in O2).
e)
Na2SO4 + Ba(OH)2 → BaSO4 + 2NaOH
  • No
  • Nothing changes oxidation state (Precipitation reaction).
f)
CH4 + 2O2 → CO2 + 2H2O
  • Yes
  • Carbon is oxidised (-4 → +4).
  • Oxygen is reduced (0 → -2).
g)
H2O2 → H2O + O2
  • Yes
  • Oxygen is reduced to H2O (-1 → -2).
  • Oxygen is oxidised to O2 (-1 → 0).
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