Determine oxidation states of elements in any chemical compound. Enter a formula and get step-by-step oxidation number assignments using standard IUPAC rules.
Enter a chemical formula (e.g. H2O, KMnO4, SO4^2-) and click Calculate to determine oxidation numbers for each element.
Water is the most common solvent on Earth. Oxygen has a higher electronegativity than hydrogen, so oxygen pulls electrons toward itself.
H: +1 (ร2) O: โ2
Check: 2(+1) + (โ2) = 0 โ
A powerful oxidizing agent. Manganese exhibits its highest common oxidation state.
K: +1 Mn: +7 O: โ2 (ร4)
Check: (+1) + (+7) + 4(โ2) = 0 โ
A common oxidizing agent used in organic chemistry. Chromium is in its +6 oxidation state.
Na: +1 (ร2) Cr: +6 (ร2) O: โ2 (ร7)
Check: 2(+1) + 2(+6) + 7(โ2) = 0 โ
A polyatomic anion with a 2โ charge. Sulfur exhibits a +6 oxidation state.
S: +6 O: โ2 (ร4)
Check: (+6) + 4(โ2) = โ2 = Charge โ
An orange-colored ion used in redox titrations. Chromium is in its +6 state.
Cr: +6 (ร2) O: โ2 (ร7)
Check: 2(+6) + 7(โ2) = โ2 = Charge โ
Oxidation numbers (or oxidation states) are bookkeeping numbers assigned to atoms in chemical compounds. They represent the hypothetical charge an atom would have if all bonds were purely ionic. They are essential for understanding redox reactions, balancing half-reactions, and predicting chemical behavior.
The calculator applies the following IUPAC-standard rules in order:
H2O, KMnO4, SO4^2-)SO4^2- for sulfate, NH4^+ for ammonium)Oxidation numbers (also called oxidation states) are a bookkeeping system used in chemistry to keep track of electron transfers in chemical reactions. They represent the hypothetical charge an atom would have if all bonds in a compound were completely ionic. This concept is fundamental to understanding redox (reduction-oxidation) reactions, which are among the most important types of chemical reactions.
The concept was developed to help chemists understand and predict how electrons move during chemical reactions. By assigning oxidation numbers, you can determine which atoms are oxidized (lose electrons, oxidation number increases) and which are reduced (gain electrons, oxidation number decreases) in a reaction.
Oxidation numbers are essential tools in many areas of chemistry:
The calculator uses the following systematic approach to assign oxidation numbers. These rules are applied in order of priority, with later rules only applying to elements not already assigned.
The most important check: ฮฃ (count ร oxidation number) = overall charge. For neutral compounds this equals 0. For ions, it equals the ion charge. This allows the calculator to solve for unknown oxidation numbers algebraically.
Understanding common patterns helps predict oxidation numbers quickly:
In most contexts, the terms "oxidation number" and "oxidation state" are used interchangeably. Strictly speaking, oxidation number is the formal charge assigned using a specific set of rules (the one used by this calculator), while oxidation state can be determined experimentally. However, for the vast majority of compounds, they give the same values.
Yes, some compounds have fractional oxidation numbers. For example, in FeโOโ (magnetite), iron has an average oxidation state of +8/3, which corresponds to a mix of Feยฒโบ and Feยณโบ ions. Similarly, in superoxides like KOโ, oxygen has an oxidation number of โยฝ. Fractional oxidation numbers indicate electron delocalization or mixed oxidation states.
The calculator accepts charge notation using the caret (^) symbol. For example, enter SO4^2- for sulfate, NO3^- for nitrate, or NH4^+ for ammonium. The calculator automatically detects the charge and ensures the sum of all oxidation numbers equals that charge. You can also use ^{2-} or (2-) notation.
Oxygen typically has an oxidation number of โ2 because it is highly electronegative and usually gains two electrons to achieve a full octet. However, in peroxides (like HโOโ), each oxygen is bonded to another oxygen, resulting in a โ1 oxidation state. In superoxides (KOโ), it's โยฝ. In oxygen difluoride (OFโ), fluorine is more electronegative, so oxygen has a +2 oxidation state.
Transition metals can have multiple oxidation states, but the correct one in a given compound is determined by the other elements present. For example, in FeClโ, chlorine's โ1 charge (ร3) tells us iron must be +3. In FeO, oxygen is โ2, so iron is +2. The calculator determines the oxidation state by applying the rules in order and solving for unknowns algebraically based on the overall charge.
Oxidation numbers are used in countless applications: balancing redox equations in chemistry labs, designing batteries and fuel cells, understanding corrosion and rust prevention, analyzing water quality (e.g., determining the oxidation state of iron or manganese in water), pharmaceutical drug synthesis, catalytic converters in cars, and even in biological systems like cellular respiration and photosynthesis where electron transfer is fundamental.
โ ๏ธ Important Note: While this calculator provides accurate oxidation number assignments for educational and general purposes, some complex compounds (especially organometallics and cluster compounds) may have ambiguous or non-standard oxidation states. Always consult authoritative references for critical applications. This tool is for reference and learning โ consult professional chemistry resources for specialized work.