ELECTROCHEMISTRY
The study of relationship between electricity and chemical reactions,
focusing on processes where electrons are transferred.
What is a redox reaction ekse?
A redox reaction is a chemical process where 1 substance loses electrons
(oxidised) and another gains those same electrons (reduced). Always
happen together.
OXIDATION NUMBERS (ON)
Used to track electron movement.
The top Golden Rules:
1. Atoms in their standard (elemental) form (O_2 (G) or Zn (s))
2. Monatomic ions ON = ions charge (Na+=+1; O2- = -2)
3. The sum Sum of ONs in neutral compound = 0. In polyatomic ion,
it = ions charge
4. Special agents:
a. Hydrogen Usually +1 (except in metal hydrides like NaH,
where it's -1).
b. Oxygen Usually -2 (except in peroxides like H₂O₂, where it's
-1).
c. Fluorine (F): Always -1.
How to solve for an unknown Oxidation No.:
Example: Find Mn's ON in MnO₄⁻.
Step:
1. Oxygens ON = -2, so 4*-2=-8
2. Total charge of ion = -1
3. Set up equation (ON of Mn) + (-8) =-1 -1+8 = ON of Mn
4. Solve and see; Mm = +7
Oxidation
Is
Loss
Reduction
Is
Gain
, Now, there’s agents (reducing and oxidizing agent)
A reducing agent (RA) gets oxidized while an oxidizing agent (OA)
gets reduced
Les do example: Zn(s) + 2H⁺(aq) → Zn²⁺(aq) + H₂(g)
Determine the RA and the OA.
Zn is the reducing agent as it loses electrons (gets oxidised)
H+ is the oxidising agent as it gains an electron and is reduced. (+1
0)
BALANCING REDOX REACTIONS:
Half-reaction method:
Split overall reaction in 2 half-reactions. 1 for Ox and 1 for Red
Step:
1. Assign Oxidation Numbers. Identify what is oxidized and reduced.
2. Write Half-Reactions
3. Balance each half-reaction
a. Balance all atoms except for H and O
b. Balance O by adding H₂O.
c. Balance H by adding H⁺.
d. Balance charge by adding electrons.
i. Ox Electrons are a product (lost electrons)
ii. Red Electrons are a reactant (gained electrons)
4. Equalise the electrons. Multiply the half-reactions by integers so
electrons gained = electrons lost
5. Add the half-reactions, combining the half-reactions will cancel out
the electrons (and anything else that appears on both sides.
6. Check to see if mass as well as charge are balanced.
Lets look at balancing in basic solution
Step:
1. Balance reaction as if it were in acidic solution (using the steps
above, with H⁺ and H₂O).
2. Add an equal number of OH⁻ ions to both sides of the equation
to neutralize all the H⁺ ions.
3. Combine H⁺ and OH⁻ on the same side to form H₂O.
4. Cancel any duplicate H₂O molecules.
The study of relationship between electricity and chemical reactions,
focusing on processes where electrons are transferred.
What is a redox reaction ekse?
A redox reaction is a chemical process where 1 substance loses electrons
(oxidised) and another gains those same electrons (reduced). Always
happen together.
OXIDATION NUMBERS (ON)
Used to track electron movement.
The top Golden Rules:
1. Atoms in their standard (elemental) form (O_2 (G) or Zn (s))
2. Monatomic ions ON = ions charge (Na+=+1; O2- = -2)
3. The sum Sum of ONs in neutral compound = 0. In polyatomic ion,
it = ions charge
4. Special agents:
a. Hydrogen Usually +1 (except in metal hydrides like NaH,
where it's -1).
b. Oxygen Usually -2 (except in peroxides like H₂O₂, where it's
-1).
c. Fluorine (F): Always -1.
How to solve for an unknown Oxidation No.:
Example: Find Mn's ON in MnO₄⁻.
Step:
1. Oxygens ON = -2, so 4*-2=-8
2. Total charge of ion = -1
3. Set up equation (ON of Mn) + (-8) =-1 -1+8 = ON of Mn
4. Solve and see; Mm = +7
Oxidation
Is
Loss
Reduction
Is
Gain
, Now, there’s agents (reducing and oxidizing agent)
A reducing agent (RA) gets oxidized while an oxidizing agent (OA)
gets reduced
Les do example: Zn(s) + 2H⁺(aq) → Zn²⁺(aq) + H₂(g)
Determine the RA and the OA.
Zn is the reducing agent as it loses electrons (gets oxidised)
H+ is the oxidising agent as it gains an electron and is reduced. (+1
0)
BALANCING REDOX REACTIONS:
Half-reaction method:
Split overall reaction in 2 half-reactions. 1 for Ox and 1 for Red
Step:
1. Assign Oxidation Numbers. Identify what is oxidized and reduced.
2. Write Half-Reactions
3. Balance each half-reaction
a. Balance all atoms except for H and O
b. Balance O by adding H₂O.
c. Balance H by adding H⁺.
d. Balance charge by adding electrons.
i. Ox Electrons are a product (lost electrons)
ii. Red Electrons are a reactant (gained electrons)
4. Equalise the electrons. Multiply the half-reactions by integers so
electrons gained = electrons lost
5. Add the half-reactions, combining the half-reactions will cancel out
the electrons (and anything else that appears on both sides.
6. Check to see if mass as well as charge are balanced.
Lets look at balancing in basic solution
Step:
1. Balance reaction as if it were in acidic solution (using the steps
above, with H⁺ and H₂O).
2. Add an equal number of OH⁻ ions to both sides of the equation
to neutralize all the H⁺ ions.
3. Combine H⁺ and OH⁻ on the same side to form H₂O.
4. Cancel any duplicate H₂O molecules.
