Balancing Redox Reactions

A reaction in which a reducing agent loses electrons while it is oxidized and the oxidizing agent gains electrons while it is reduced is called as redox (oxidation – reduction) reaction. An unbalanced redox reaction can be balanced using this calculator.

Calculator of Balancing Redox Reactions

Redox Reaction is a chemical reaction in which oxidation and reduction occurs simultaneously and the substance which gains electrons is termed as oxidizing agent.
Refer the following table which gives you oxidation numbers.

Table of Common Ions

Positive Ions

Valency 1		Valency 2		Valency 3
Lithium	Li⁺	Magnesium	Mg²⁺	Aluminium	Al³⁺
Sodium	Na⁺	Calcium	Ca²⁺	Iron III	Fe³⁺
Potassium	K⁺	Strontium	Sr²⁺	Chromium	Cr³⁺
Silver	Ag⁺	Barium	Ba²⁺
Hydronium	H₃O⁺	Copper II	Cu²⁺
Hydrogen	H⁺	Lead II	Pb²⁺
Ammonium	NH₄⁺	Zinc	Zn²⁺
Copper I	Cu⁺	Manganese II	Mn²⁺
Mercury I	Hg⁺	Iron II	Fe²⁺
		Tin II	Sn²⁺

Negative Ions

Valency 1		Valency 2		Valency 3
Fluoride	F^–	Oxide	O^2-	Phosphate	PO₄^3-
Chloride	Cl^–	Sulphide	S^2-
Bromide	Br^–	Carbonate	CO₃^2-
Iodide	I^–	Sulphate	SO₄^2-
Hydroxide	OH^–	Sulphite	SO₃^2-
Nitrate	NO₃^–	Dichromate	Cr₂O₇^2-
Bicarbonate	HCO₃^–	Chromate	CrO₄^2-
Bisulphate	HSO₃^–	Oxalate	C₂O₄^2-
Nitrite	NO₂^–	Thiosulphate	S₂O₃^2-
Chlorate	ClO₃^–	Tetrathionate	S₄O₆^2-
Permanganate	MnO₄^–	Monohydrogen Phosphate	HPO₄^2-
Hypochlorite	OCl^–
Dihydrogen Phosphate	H₂PO₄^–

Example: 1

Balance the given redox reaction:

H₂⁺ + O₂^2- -> H₂O

Considering the equation above, we have 2 hydrogen (H) with the total charge +1[Refer the charges of the elements in the above table] and 2 oxygen (O) with the total charge -2 on the L.H.S and 2 hydrogen (H) with total charge +2 and only 1 oxygen (O) with the total charge -2 on the R.H.S. Hence with the unequal number of oxygen molecule charges, the chemical equation is said to be unbalanced.

How to balance an unbalanced chemical equation?

Let us learn here how to balance the above unbalanced equation using half reaction method with step by step procedure.

Given,

H⁺¹₂ + O^-2₂ -> H⁺¹₂ O^-2

To balance the unbalanced oxygen molecule charges, we add 2 in front of the product on R.H.S.
We get,

H⁺¹₂ + O^-2₂ -> (2) H⁺¹₂ O^-2

Now, we have 2 Oxygen’s with the total charge -2 but 4 Hydrogen’s with the total charge +4 on the R.H.S.
In order to balance the same, we add an another 2 in front of Hydrogen on the L.H.S

(2) H⁺¹₂ + O^-2₂ -> (2) H⁺¹₂ O^-2

Now, the equation is balanced with 4 Hydrogen’s (H) with total charge +4 and 4 Oxygen’s with total charge -4 on both sides.

Example: 2

Cr⁺³ + Cl^-1 = Cr⁺³ + Cl^-1₂

Considering the equation above, we have 1 chromium (Cr) with the total charge +3[Refer the charges of the elements in the above table] and 1 chloride (Cl) with the total charge -1 on the L.H.S and 1 chromium (Cr) with total charge +3 and only 2 chloride(Cl) with the total charge -1 on the R.H.S. Hence with the unequal number of oxygen molecule charges the chemical equation is said to be unbalanced.

How to balance an unbalanced chemical equation?

Let us learn here how to balance the above unbalanced equation with step by step procedure.

Given:

Cr⁺³ + Cl^-1 = Cr⁺³ + Cl^-1₂

To balance the unbalanced chloride molecule charges, we add 2 in front of the chloride on L.H.S.
We get,

Cr⁺³ + (2)Cl^-1 = Cr⁺³ + Cl^-1₂

Now, the equation is balanced with 2 Chloride’s (Cl) with total charge -2 and 3 Chromium’s with total charge +3 on both sides.
This is how the redox equations are balanced.

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