"Unlock Success with Comprehensive Study Notes!
Are you tired of sifting through endless textbooks and lecture notes? Do you wish you had a reliable resource to help you ace your exams and assignments? Look no further! I'm offering meticulously crafted study notes that cover the key concepts, in...
INTRODUCTION
The process in which it involves the loss of
electrons by the atoms or ions is termed as Concept Ladder
Oxidation.
One of the most important
The process in which it involves the gain of
processes that occurs
electrons by the atoms or ions is termed as
in living organisms is
Reduction.
photosynthesis, which
Those reactions, in which reduction and oxidation
consists of a series of
takes place simultaneously is called a Redox
oxidation-reduction
Reaction. The species that lose electrons (i.e.,
reactions.
gets oxidised) is known as reducing agent or
reductant, the species which accepts electrons
from reductant (i.e., gets reduced) is known as
oxidising agent or oxidant.
Ex.
Mg + Zn2+ → Mg 2+ + Zn is a redox reaction.
0 2+ Rack your Brain
Oxidation : Mg
→ Mg + 2e−
0
+2 Why this reaction is not redox
Reduction : Zn + 2 e−
→ Zn
reaction?
Mg causes reduction of Zn2+, so it is Reductant. NaOH +HCl → NaCl +H2O
Zn2+ causes oxidation of Mg, so it is Oxidant.
Oxidation Number (O.N.) : It refers to the total
charge on all atoms of same kind in a compound.
Oxidation State (O.S.) : It refers to the charge per
atom of all atoms of same kind in a compound.
In a compound O.N. of an element is equal to
oxidation state of that element multiplied by total
Previous Year’s Questions
atoms of that element in particular compound.
Hot concentrated sulphuric acid
(i) In ionic compounds, it is simply the
is a moderately strong oxidizing
charge on corresponding cation and anion
agent which of the following
which is expressed as oxidation state
reactions does not show oxidizing
of that particular element. For example,
behaviour
oxidation state of potassium and chlorine
[NEET]
in potassium chloride (KCl) is simply +1 and
(1) Cu + 2H SO
→ CuSO + SO2 + 2H2O
–1 respectively as KCl is treated as K+Cl–.
2 4 4
(2) S + 2H2SO4 → 3 SO2 + 2H2O
Refer to following examples where oxidation
Redox Reactions
(3) C + 2H2 SO 4
→ CO2 + 2 SO2 + 2H2O
states are written above the atoms :
(4) CaF2 + H2SO4 → CaSO4 + 2HF
1.
, +2 −1 +2 − 2 +3 − 1 +2 − 2 +1 − 1 +1 +6 − 2
Mg Cl 2 Ca S Al Cl 3 Ca O Na F K2S O4
(ii)
In Covalent Compounds, it is not 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 of every element
in any compound.
Rules for Assigning Oxidation state (O.S.) and
Concept Ladder
Oxidation Number (O.N.)
(i) Any element in elemental state is assigned When a covalent bond
an oxidation state of zero. For example: O.S. forms between two
of H, P, S, O, Fe, Br in H2, P4, S8, O2, Fe, Br2 is atoms with different
equal to 0. electronegativities the
(ii) The oxidation state of any cation or anion shared electrons in the
(of form A+ or B–) is equal to the magnitude bond lie closer to the more
of its charge. For example: O.S. of Ca in Ca2+ electronegative atom: The
= +2, O.S. of Al in Al3+ = +3, O.S. of Cl in Cl– = oxidation number of an
–1 and so on. atom is the charge that
(iii) (a) The algebraic sum of the oxidation results.
number of all atoms in neutral
compounds is equal to 0.
(b) The algebraic sum of the oxidation
numbers of all atoms in an ion (like
PO34− etc.) is equal to the ion’s charge.
(iv)
The oxidation state of Alkali Metals (Group
IA) is +1 in all of their compounds and that
of Alkaline Earth elements (Group IIA) is +2 Rack your Brain
in all of their compounds.
(v) Hydrogen in almost all of its compounds Find out the oxidation state of
is assigned an oxidation state of +1. The phosphorous in H3PO4 and H3PO3?
exception occurs when hydrogen forms
compounds with strong metals (metallic
hydrides). For example: KH, NaH, MgH2,
Redox Reactions
CaH2 etc. In all of these, the oxidation state
of hydrogen is –1.
2.
,(vi)
Oxygen in almost all of its compounds is
assigned an oxidation state of –2. In a class
of compounds, Peroxides, oxidation state of
oxygen is –1, for example : H2O2, Na2O2 etc.
Another exception is OF2, where O.S. is +2. Concept Ladder
O2F2, where O.S. is +1 and KO2 in which O.S.
1
is − . The same element can
2
have different oxidation
(vii)
Fluorine is most electronegative element state in same molecule.
and is assigned an O.S. of –1, in all its Example :
compounds. For other halogens, O.S. is oxidation state of carbon
generally –1 except when they are bonded to (C) in C3O2.
a more electronegative halogen or oxygen.
O.S. of iodine in IF7 is +7, O.S. of chlorine in
KClO3 is +5.
Concept of Fractional Oxidation State
Fractional O.S. is the average oxidation state
of the element under examination, and it means Rack your Brain
that the element for which fractional O.S. is
realized is present in different oxidation states.
Find the oxidation number of Cl
in ClO4-?
Structure of the species C3O2, Br3O8 and S4O62−
reveal the following bonding situations :
The elements marked with asterisk in the
above examples will exhibit different oxidation
state from the remaining atoms of the same
Redox Reactions
element in each of the species. This means that
in C3O2, two carbon atoms are present in +2
oxidation state each, whereas the third one is
3.
, present in 0 oxidation state and the average is
4/3. Likewise in Br3O8, each of the 2 terminal Br
atoms are present in +6 O.S. and the middle Br
atom is present in +4 O.S. and the average is 16/3.
In the same manner, in the species S4O62− is 2.5,
Concept Ladder
whereas the reality being +5, 0, 0 and +5 O.N.
respectively for each S atom. Some other Decomposition reactions
examples of the compounds are Pb3O4, Fe3O4, happen all around us, but
Mn3O4, which are mixed oxides having the metal we often don’t notice them.
in fractional oxidation state. However, the The decomposition of
oxidation states may be in fraction as in O2+ and O2− carbonic acid in soft drinks,
where it is +1/2 and –1/2 respectively. which can be represented
by the chemical equation
Analysis of a Redox Reaction H2CO3 → H2O + CO2
Consider the following Redox Reaction:
CusO4 + Pb
PbSO4 + Cu
1. Assign oxidation state of each atom.
+2 +6 −2 0 +2 +6 −2 0
Cu S O4 + Pb
→ Pb S O4 + Cu
Rewriting the equation as two equations
(oxidation and reduction) as follows :
Reduction : Cu2+ + 2e−
→ Cu0 ( gaining 2e )
−
Oxidation : Pb0
→ Pb2+ + 2e− (losing 2e )
−
We can now re-define oxidation and
reduction as follows :
Oxidation is an increase in oxidation state
and reduction is a decrease in oxidation
Rack your Brain
state.
The reaction 2Pb(NO3)2 →
Types of Redox Reaction 2PbO + 4NO2 + O2 is a type of
1. Combination reactions _______reaction?
It may be denoted in the manner :
A + B → C
All combustion reactions, which make use
of reactions involving elements other than
Redox Reactions
dioxygen as well as elemental dioxygen, are
redox reactions. Some important examples
of this category are :
4.
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card or Stuvia-credit for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller zsstudynotes. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for $6.49. You're not tied to anything after your purchase.
