Redox reactions

Question 1

What is oxidation?

Answer 1

• *O**xidation
• *I**s
• *L**oss of electrons.

Oxidation state increases; number goes up.

Gain of oxygen,
Loss of hydrogen.

Question 2

What is an oxidising agent?

Answer 2

• Oxidising agents are electron acceptors.
• They themselves are reduced (gain electrons) whilst oxidising the other substance (taking electrons away).

Question 3

What is reduction?

Answer 3

• *R**eduction
• *I**s
• *G**ain of electrons.

Oxidation state decreases; number goes down.

Loss of oxygen,
Gain of hydrogen.

Question 4

What is a reducing agent?

Answer 4

• Reducing agents are electron donors.
• They themselves are oxidised (lose electrons) whilst reducing the other substance (giving electrons to them.

Question 5

State the oxidation states of the following:

• Hydrogen, H
• Group 1 compounds
• Group 2 compounds
• Oxygen, O
• Fluorine, F
• Chlorine, Cl

Answer 5

Oxidation states are the number of electrons lost or gained relative to the normal amount
of electrons for that atom.

• Hydrogen, H: +1 (except in metal hydrides such as NaH where it is -1)
• Group 1 compounds: Always +1
• Group 2 compounds: Always +2
• Oxygen, O: -2 (except in peroxides and compounds with F, where it is -1 and +2 in OF₂)
• Fluorine, F: Always -1
• Chlorine, Cl: -1 (except in compounds with F and O, where it has the corresponding +ve value)

In a compound the most electronegative element always has a negative oxidation state.

Question 6

How do you balance a redox equation?

Answer 6

• *A**toms (balance, but don’t do H or O)
• *O**x. No. (write them out)
• *E**lectrons (add to relevant side)
• *B**alance charge with H+ (if in acid, OH^- if alkali)
• *H**₂O (add to other side to balance H’s and O’s)
• *C**heck
• *A**ll
• *O**tters
• *E**at
• *B**acon Cobs
• *W**ith
• *C**heese

Half equations

Equations which show elements losing or gaining electrons such as Cu to Cu2+

Cu > Cu²⁺ + 2e^-

Redox Equations

Using two half equations already worked out, you can produce a full equation including all
charges and elements but without electrons, such as the reaction between copper and
cold dilute nitric acid

3Cu + 8H⁺ + 2NO₃- > 3Cu²⁺ + 2NO + 4H₂O

Question 7

How do you form an ionic equation?

HCl + NaOH > NaCl + H₂O