![]() They oxidise others, themselves are reduced & gain electrons. States except zero in free stateĪ reaction in which oxidation & reduction occur simultaneously. Actually, Fe 3O 4 is made up of equimolar quantity of FeO and Fe 2O 3.Ĭommon oxid. ![]() This is the average oxidation state of Fe in Fe 3O 4. Thus, oxidation state of Fe in Fe 3O 4 is +8/3. (f) Let the oxidation state of Fe in Fe 3O 4 be x. Thus, oxidation state of Fe in Fe 2O 3 is +3. ![]() (e) Let x be the oxidation state of Fe in Fe 2O 3. Thus, oxidation state of Cr in Cr 2 O 7 2 − is +6. (d) Let the oxidation state of Cr in Cr 2 O 7 2 − be x. Thus, oxidation state of Mn in KMnO 4 is + 7. (c) Let the oxidation state of KMnO 4 be x. Thus, oxidation state of N in NO 3 − is + 5. (b) Let x be the oxidation state of N in NO 3 −. Thus, oxidation state of N in NO 2 + is +5. (a) Let the oxidation state of N in NO 2 + be x. Illustration: Calculate the oxidation state of the underlined atoms in the given species. (xii) The sum of oxidation number of all the atoms in a molecule should be zero and in an ion equal to its charge. (xi) Oxidation number of a molecule as a whole is zero. (x) Oxidation number of an ion is equal to its charge. (ix) Oxidation number of alkaline earth metals in their compounds is + 2. (viii) Oxidation number of alkali metals in their compounds + 1. (vii) Oxidation number of O is – 2 in its compounds, but in F 2O it is + 2 and in peroxides it is – 1 and – 0.5 in K O 2. (vi) Oxidation number of H in its compounds is + 1, except in metal hydrides where it is – 1. (v) Oxidation number of F in compounds is – 1. (iv) Oxidation number of mono-atomic ions is equal to the algebric charge on them. (iii) Oxidation number of atoms in homo-nuclear molecules is zero. (ii) Oxidation number of allotropes is zero. (i) Oxidation number of free elements or atoms is zero. There are certain set of rules used to assign oxidation states in polyatomic molecules: To calculate the oxidation state of an element in a molecule you need not always know the structure of the molecule. This is because O–O bond can not be assumed to be ionic as both the atoms have the same electronegativity. Considering each O–H bond to be ionic both the oxygen atoms acquire a charge of -1 and both the H, +1. On the other hand, in H 2O 2 there are two O–H bonds and one O–O bond. This is because oxygen is more electronegative than hydrogen. If we assume both the O–H bonds to be completely ionic, then each H would possess a charge of +1, while O possess a charge of –2. For example in H 2O there are two O–H bonds. Therefore, the Oxidation State (O.S.) or Oxidation Number (O.N.) is defined as the charge, an atom would have in a molecule if all the bonds associated with this atom in the molecule are considered to be completely ionic. But in covalent molecules, the charge on an atom would be so small that sometimes it becomes impossible to calculate the exact charge on each atom of a molecule. Therefore the oxidation state of Na in NaCl is +1 and that of Cl- is – 1. ![]() For example in NaCl, Na exists as Na+ and Cl exists as Cl. For ionic species, the charge on each ion is said to be the oxidation state for that atom. To describe these changes, the concept of oxidation state becomes necessary. There are several chemical reactions in which oxidation – reduction takes place. There are some operational rules to determine oxidation number.Ĭalculation of Oxidation State / Oxidation Number It may be a whole number or fractional, it depends on nature of compound in which it is present. If all the polar covalent bonds of molecule are assumed to be 100% ionic then the charge appeared on corresponding atoms is known as their oxidation states. It is the charge which an atom appears to have when it is in combination.
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