Redox Reaction
Redox Reaction
Introduction
The redox reaction is related to gain or loss of electrons. A reaction in which oxidation and reduction takes place simultaneously is called redox reaction. This chapter deals with problems based on redox reactions, oxidation number, and balancing of redox reactions by ion, electron method, and oxidation number method.
Oxidation Reactions
Oxidation is defined as the addition of oxygen/electronegative element to a substance or removal of hydrogen/ electropositive element from a substance.
2Mg(s) + O2(g) ⟶ 2MgO(s)
Mg(s) + Cl2(g) ⟶ MgCl2(s)
Reduction Reactions
Reduction is defined as the removal of oxygen/electronegative elements from a substance or the addition of hydrogen or electropositive elements to a substance.
2FeCl3(aq) + H2(g) ⟶ 2FeCl2(aq) + 2HCl(aq)
2HgO(s) ⟶ 2Hg(l) + O2(g)
Oxidation Number or Oxidation State
The oxidation number for an element is the arbitrary charge present on one atom when all other atoms bonded to it are removed. For example, if we consider a molecule of HCl, the Cl atom is more electronegative than the H-atom, therefore, the bonded electrons will go with a more electronegative chlorine atom resulting in the formation of H+ and Cl– ions. So, the oxidation numbers of H and Cl in HCl are +1 and –1 respectively.
The following points are important to determine the oxidation number of an element.
1. The oxidation number of an atom in pure elemental form is considered to be zero. e.g., H2, O2, Na, Mg.
2. The oxidation number of any element in a simple monoatomic ion will be equal to the charge on that ion, for example, the oxidation number of Na in Na+ is +1.
3. The oxidation number of fluorine in its compound with other elements is always -1.
4. The oxidation number of oxygen is generally -2 but in the case of peroxide (H2O2), oxygen has an oxidation number of -1. In a compound OF2, the oxidation number of oxygen is +2.
5. The oxidation number of alkali metals (Na, K) and alkaline earth metals (Ca, Mg) are +1 and +2 respectively.
6. The oxidation number of halogens is generally -1 when they are bonded to less electronegative elements.
7. The oxidation number of hydrogen is generally +1 in most of its compounds but in the case of metal hydride (NaH, CaH2) the oxidation number is hydrogen is -1.
8. The algebraic sum of the oxidation numbers of all the atoms in a neutral compound is zero. In an ion, the algebraic sum of the oxidation number is equal to the charge on that ion.
Redox Reaction
Rest notes are available in the PDF attached
