U3AOS1 Topic 5: Redox Basics

What is Redox?

Redox reaction involves the transfer of electrons 

When breaking the word down, red - stands for reduction and ox - stands for oxidation

Reduction cannot occur without oxidation occurring simultaneously and vice versa

Reduction is the gain of electron(s)

Oxidation is the loss of electron(s)

Now where does the electron gained during reduction come from? It can’t just magically appear

It comes from the species undergoing oxidation

Hence, both reduction and oxidation must occur together

Remember how depending on the group that the element sits in, the valence electron number can be determined (exclusive of transition metals from groups 3 to 12)

Eg. Sodium (Na) is in group 1 therefore has 1 valence electron, Fluorine (F) is in group 17 therefore has 7 valence electrons

All elements ‘try’ to have a full valence shell of 8 electrons as per the octet rule. Thus, gaining stability therefore halogens (group 17) gain an electron via reduction to become an anion whilst alkali metals (group 1) lose an electron via oxidation to become a cation.

Half equations

Half equations only represent either oxidation or reduction, not both at the same time.

Oxidation:

Ag(s) →Ag3+(aq) + 3e- Check if e-  is on right side of equation to verify oxidation

2Cl-(aq) →Cl2(g) + 2e-

Reduction:

Na+(aq) + e- →Na(s) Check if e- is on left side of equation to verify reduction

Br2(l) +2e- → 2Br-(aq)

Normal tip: Ensure the charges are balanced on both sides, as you can see the net charge on left hand side is 0 and on the right it's also 0 (+3-3=0)

Source: (JavaLab - Activity Series of Metals, https://javalab.org/en/activity_series_of_metals_en/)