Oxidation State Calculator for Compounds, Ions, and Redox Analysis

Calculator input

Enter the chemical formula without charge signs, choose the element to solve, add the overall ion charge, and provide any special known values when needed.

Chemical Formula

Supports parentheses, brackets, and hydrates like CuSO4·5H2O.

Target Element

Enter the element whose oxidation state must be solved.

Overall Charge

Use 0 for neutral compounds, +1 for NH4+, -2 for Cr2O7²⁻.

Known Oxidation States

Use commas, semicolons, or new lines. Example: Cl=-1, O=-1.

Use Common Rules

Apply defaults like O = -2, H = +1, F = -1, Group 1 = +1, Group 2 = +2

Example data table

Formula	Target	Charge	Known States	Expected Result
H2SO4	S	0	H=+1, O=-2	S = +6
KMnO4	Mn	0	K=+1, O=-2	Mn = +7
NH4	N	+1	H=+1	N = -3
Cr2O7	Cr	-2	O=-2	Cr = +6
Fe2O3	Fe	0	O=-2	Fe = +3

Formula used

Core relation: the sum of all atomic oxidation contributions equals the total charge on the species.

Σ(n_i × OS_i) = Q

Here, n_i is the atom count, OS_i is the oxidation state of each element, and Q is the overall charge.

For one unknown target element x:

x = (Q − Σ known contributions) / number of target atoms

Example for sulfate sulfur in H₂SO₄: 2(+1) + x + 4(-2) = 0, so x = +6.

How to use this calculator

Type the formula without adding plus or minus signs at the end.
Enter the symbol of the element you want to solve.
Set the overall charge. Use zero for neutral molecules.
Keep common rules checked for standard compounds and simple ions.
Add overrides for special cases like peroxides, superoxides, hydrides, or unusual halogen values.
Press the calculate button to show the result above the form.
Review the equation, contribution table, and graph for verification.
Download the result as CSV or PDF for study records.

Eight FAQs

1. What does oxidation state mean in chemistry?

Oxidation state is the formal charge an atom would have if bonding electrons were assigned by standard bookkeeping rules. It helps track electron transfer, redox changes, and charge balance in compounds and ions.

2. Why can oxidation state differ from actual ionic charge?

Oxidation state is a formal accounting tool, not always a measured charge. Covalent compounds often share electrons, so real charge distribution can differ from the oxidation number used in balancing and analysis.

3. Why does oxygen usually have an oxidation state of -2?

Oxygen is highly electronegative and commonly takes two electrons in formal assignments, giving -2. Important exceptions include peroxides, superoxides, and compounds with fluorine, where oxygen can differ.

4. Why does hydrogen sometimes become -1?

Hydrogen is usually +1 with nonmetals, but in metal hydrides it is assigned -1. The bonding partner matters, so special cases should be entered through the known-state override field.

5. Can this calculator solve every compound automatically?

Not always. If more than one non-target element has an unknown value, extra information is needed. Add known oxidation states manually for special or ambiguous compounds to complete the calculation.

6. What does a fractional result mean?

A fractional output often indicates an average oxidation state, common in mixed-valence systems or formulas that summarize several atomic environments. The formal average is still useful for balancing and interpretation.

7. How should I enter polyatomic ions?

Enter the plain formula and place the total ion charge in the charge field. For example, use NH4 with charge +1 or Cr2O7 with charge -2. Do not place charge signs inside the formula box.

8. Why is an equation shown with the answer?

The displayed equation makes the result transparent. You can inspect each element’s contribution, verify the charge balance manually, and confirm that the solved oxidation state follows the bookkeeping rules correctly.