Oxidation
It is a process that involves the loss of electrons by the atoms or ions.
Reduction
It is a process that involves the gain of electrons by the atoms or ions.
Any reaction, in which the electrons are exchanged between atoms or ions, represents a simultaneous process of oxidation and reduction and is called as a Redox Reaction.
In a Redox Reaction, the species that loses electron (i.e., gets oxidised) is known as reducing agent or reductant, (since it causes reduction of other species), the species which accepts electrons from reductant (i.e., gets reduced) is known as oxidising agent or oxidant (as it causes oxidation of other species).
Oxidation State (O.S.): It refers to the hypothetical charge on atoms in a compound if all the bonds were assumed to be 100% ionic.
Oxidation state, many times, is also referred to as Oxidation Number.
This means oxidation number of an element in a compound is equal to the oxidation state of that element multiplied by total atoms of that element in a particular compound.
(i) In ionic compounds, it is simply the charge on corresponding cation and anion which is expressed as the oxidation state of that particular element. For example, the oxidation state of potassium and chlorine in potassium chloride (KCl) is simply +1 and –1 respectively as KCl is treated as K+Cl–.
Refer to the following examples where oxidation states are written above the atoms:
+2-1 | +2-2 | +3-1 | +1+6-2 |
MgCl2 | CaS | AlCl3 | K2SO4 |
NOTE: (a) In MgCl2 and AlCl3, -1 is the oxidation state of Cl.
(b) In each of the cases, the sum of oxidation number of all atoms of all kinds is equal to zero since the compound is neutral.
(ii) In Covalent Compounds, it is not so easy to assign oxidation state of an atom. In order to simplify the concept, we are going to define a set of rules which would enable us to assign oxidation state to every element in any compound.
Rules for Assigning Oxidation State (O.S.) and Oxidation Number (O.N.):
The algebraic sum of the oxidation number of all atoms in a neutral compound is equal to 0. The algebraic sum of the oxidation numbers of all atoms in an ion (like PO43-) is equal to charge on the ion.
The oxidation states of Alkali Metals (Group IA) is +1 in all of their compounds and that of Alkaline Earth elements (Group IIA) is +2 in all of their compounds.
Hydrogen in almost all of its compounds is assigned an oxidation state of +1. The exception occurs when hydrogen forms compounds with strong metals like KH, NaH, MgH2, CaH2, etc. In all of these, the oxidation state of hydrogen is -1.
Oxygen in almost all of its compounds is assigned an oxidation state of -2. But in certain compounds like Peroxides(H2O2), the oxidation state of oxygen is -1. Another exception is OF2, where O.S. is +2. O2F2, where O.S. is +1 and KO2 in which O.S. is -1/2.
Fluorine is most electronegative element and is assigned an O.S. of -1, in all its compounds. For other halogens, O.S. is generally -1 except when they are bonded to a more electronegative halogen or oxygen. O.S. of iodine in IF7 is +7, O.S. of chlorine in KClO3 is +5.
Generally, an element with greater electronegativity is assigned -1 by hypothetical breaking of one covalent bond.
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JEE MAIN | Redox Reaction and Electrochemistry |
Which of the following substances is oxidised in the following reaction:
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Select the redox change in the following reaction
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Oxidants are substances which
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In which compound does Vanadium have an oxidation number of +4?
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Which of the following is reduced in the following reaction?
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Select the type of redox change in the following reaction:
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Reductants are substances which
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When KMnO4 acts as an oxidising agent and ultimately forms then the number of electrons transferred in each case respectively is
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Which of the following is a redox reaction?
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Which of the following chemical reactions depict the oxidising behaviour of ?
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Arrange in increasing order of oxidation number of N:
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Identify the oxidation number of V in ions respectively.
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Arrange the following in increasing order of oxidation number of Fe:
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Determine the oxidation numbers of the following:
N atoms in , Fe in and Cr in
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The correct order of the oxidation states of nitrogen in and is :
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What is the oxidation number of Cr in ?
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What is the oxidation number of Cr in ?
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What is the oxidation number of Ba in ?
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Which of the following metal has more oxidation number in ?
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What is the oxidation number of Na in NaH?
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Find the O.N. of Ca in ?
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What is the O.N. of Cl in ?
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What is the oxidation number of CI in CIF?
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The oxidation number of potassium in respectively is :
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Which of the following reactions is a redox reaction?
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Identify the process in which change in the oxidation state is five :
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In polythionic acid, the oxidation state(s) of sulphur is/are :
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Consider the following reduction processes
The reducing power of the metals increases in order:
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In reaction with stronger oxidizing agents like KIO4, hydrogen peroxide oxidizes with the evolution of O2The oxidation number of I in KIO4 changes to __________.
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Experimentally it was found that a metal oxide has formula M0.98O.Metal M, is present as M2+and M3+ in its oxide. Fraction of the metal which exists as M3+ would be:
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What is the oxidation number of P in P4?
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What is the sum of the oxidation numbers of all the atoms in ?
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Find the oxidation number of the atom in ?
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What is the oxidation state of in
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For an ideal gas, number of moles per litre in terms of its pressure , gas constant and temperature is
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Arrange the following species in decreasing order of oxidation numbers:
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The possible oxidation state of oxygen is
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In which of the following molecule nitrogen has highest oxidation state ?
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Oxidiation states of P in and are respectively
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In Chromyl chloride, the oxidation state of chromium is (+) ______.
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Which element undergoes oxidation as well as reduction in the following reaction?
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The average oxidation states of sulphur in and are:
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Match the following:
Compound(atom) | Oxidation State of Atom |
(I) | (A) +1 |
(II) | (B) -1 |
(III) | (C) +2 |
(IV) | (D) +7 |
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The oxidation number of Mn in is :
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Arrange the following compounds based on increasing oxidation state:
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In the reaction , the species that is oxidised and the species that is reduced is:
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Match the following:
compound | oxidation state |
(I) | A) +6 |
(II) | B) +1 |
(III) | C) -2 |
(IV) | D) +4 |
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Match the following:
compound | oxidation state |
(I) | A) +2 |
(II) | B) +7 |
(III) | C) +6 |
(IV) | D) +4 |
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For the reaction:
What is the oxidation state changes of Sulphur?
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What is the oxidation state of sulphur in Dithionic acid and sulfoxylic acid?
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Which of the following is a self-indicator?
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Eriochrome T is not used as an indicator for which of the following metals?
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Which of the following species do not disproportionate?
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What is the oxidation state of in and in ?
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What are the two oxidation states present in ?
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For the reaction: , what is the oxidation half reaction?
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Which of the following compounds exhibit a oxidation state for oxygen?
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What is the oxidation State of nitrogen in ?
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Match the following with the oxidation state of chlorine:
Compound | Oxidation state |
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What are the two oxidation states in thiosulfurous acid?
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What is the oxidation state of nitrogen in peroxynitrous acid?
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Metaboric acid dehydrates to form pyroboric acid. What is the change in oxidation state change?
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Hypophosphate salts on standing in air convert into pyrophosphates. What is the change in oxidation state?
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How many of these oxoacids have sulphur in oxidation state?
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Which of the following sulfur oxoacids has sulfur in 0 oxidation state?
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Metaperiodic acid reacts with hot water to give
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Match the following:
Compound | Oxidation State |
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III) | C) |
IV) | D) |
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Which of the following oxoacids have phosphorus in oxidation state?
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What is the oxidation state of in Ruthenic acid?
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Arrange the following oxoacids based on increasing oxidation state:
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$\mathrm{Br}_2+\underset{\text { hot }+ \text { conc. }}{\mathrm{NaOH}} \longrightarrow \mathrm{NaBr}+X+\mathrm{H}_2 \mathrm{O}$
Sum of stoichiometric coefficients of $\mathrm{Br}_2\: \: \&\: \: \mathrm{NaOH}$ in balanced equation is.
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From the given list, the number of compounds with +4 oxidation state of Sulphur is _________ .
$\mathrm{SO}_3, \mathrm{H}_2 \mathrm{SO}_3, \mathrm{SOCl}_2, \mathrm{SF}_4, \mathrm{BaSO}_4, \mathrm{H}_2 \mathrm{~S}_2 \mathrm{O}_7$
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Which of the following cannot function as an oxidising agent?
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In chromyl chloride test for confirmation of $\mathrm{Cl}^{-}$ion, a yellow solution is obtained. Acidification of the solution and addition of amyl alcohol and $10 \% \mathrm{H}_2 \mathrm{O}_2$ turns organic layer blue indicating formation of chromium pentoxide. The oxidation state of chromium in that is :
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The oxidation number of iron in the compound formed during brown ring test for $\mathrm{NO}_3^{-}$ion is_________.
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Reduction potential of ions are given below:
$\begin{array}{ccc}\mathrm{ClO}_4^{-} & \mathrm{IO}_4^{-} & \mathrm{BrO}_4^{-} \\ \mathrm{E}^{\circ}=1.19 \mathrm{~V} & \mathrm{E}^{\circ}=1.65 \mathrm{~V} & \mathrm{E}^{\circ}=1.74 \mathrm{~V}\end{array}$
The correct order of their oxidizing power is.
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In the reaction of potassium dichromate, potassium chloride and sulfuric acid (conc.), the oxidation state of the
chromium in the product is (+) ________ .
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In acidic medium, $\mathrm{K}_2 \mathrm{Cr}_2 \mathrm{O}_7$ shows oxidizing action as represented in the half reaction. $\mathrm{Cr}_2 \mathrm{O}_7^{2-}+\mathrm{XH}^{+}+\mathrm{Ye}^{-} \rightarrow 2 \mathrm{~A}+\mathrm{ZH}_2 \mathrm{O}$
$\mathrm{X}, \mathrm{Y}, \mathrm{Z}$ and $\mathrm{A}$ respectively are :
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A less obvious example of electron transfer is realised when hydrogen combines with oxygen to form water by the reaction: