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CHAPTER NO. 6 - REDOX ~F:ACTION

Classical DEFINITIONS:

1. Oxidation is defined as;

• addition of oxygen
• addition of electronegative e?ement
• removai of hydrogen·
• re1noval of electropositive element
• loss of electrons by any species (electron donor)

u. Reduction is defined as;

• removal of oxygen •
• removal of electronegative element
• addition of hydrogen .·
• addition of electropositive element
• gain of electrons by any species (electron acceptor)

a1. Oxidant/oxidi zing agent is .defined as; .

A reagent/substa nce which itself undergoes reduction. and causes oxidation· ofanother specit!s is -
called oxidant or oxidizing agent. This is an electron acceptor.

iv. Reductant/Re ducinl! agent is d~lincd as;

. .
A reagent/substa nce which· itsdf undergoes oxidation and causes reduction of another species is
called reductant or·reducing ~g.~nt. This is an electron donor.

v. Redox Reaction is defined as:

A chen1ical reaction, in which one of the· reactant undergoes oxidation wh~reas the other reactant
undergoes reduction SIMULTANEOUSL v:

Definitions on the basis of electron transfer

•• · i. •Oxfdation: It. is defmed as

•On·e OT rrt(>re 4 (!)~cffon's: I ,• ; .f f
aprocess in ,which an atom~ ion or group of atoms donates (or loses)
•. \ ... • • . , • : . • • • .-., •

~-; .·,.,;:li ..... • •·:• . . ,-;•

.It is aJso caJled ·de-electro1~ation.

'
ii. Reduction: It is defined as a process in which an atom, ion or group of~·Homs accepts (or
gains) one or mor·e e)ectrons. .. .
.. . .. )

It is also called electronation

iii. Oxidising agent: It is dl'linl?d ,1s·.1 substance which rn:cepts one or more electrons and
oxidises the other substance. Itself' undcn!.o~s reduction. '-

iv.rz.educin!.! aucnt: It is c.klincd .is ,1 :-,uhstancc

'- '- . which du11:.lles one or more electrons ;ind reduces
other substances. Itself urnkrgoL'S u.,id,ition.
 ..

y. Rcdox rcnctio
n: 1t is de lined ·as . lion which on
ckclmn w hl!reas the other achem
one
ical reac ULin e
TANEOUSLoy(.th~ r~uclant donates
accepts electron •.
()XIDATION SIM
NUMBER •
· ·
0:xH.\ntifmNu
mbero•fanelem .
carn•cs: ,,sstum. entmacompoun d • \ 1·111ed as th
ng complete el is le . ' e number o f electrica
Definitions in
. ectron trans,rer m
• th •a
e c, • covalent bon d•.
sc ol- l char •
ges,t
terms of oxidat . •
ion number- • . .
i. Oxidatio n - An increase
in the oxidation
ii. Reduction number of an cl
-Adecrease in the
oxidation numbe
ement'in a giv
en Subslance.
iii. Oxidisirig , r of an element in
. ag a given sub 5lc
g.i,·en substan e n t- A substance which increa 1ncc.
ce, and itself u
ndergoes decrea ses their oxidation number o
se in oxidation f
iv. Reducing
a g e n t- A subst number of a co an element in a
substance. an ance that decrea n stituent element.
d itself underg ses the oxidatio
oes an increase n
v. Redox Rea in the oxidation numb(!r o f an element in a
number of a con gi\'e
,v h e re a s that
ction - It is def
ined as the reac stituent elemen n
of other decreas tion t.
es SIMULTAN in which oxidation number
RLILES FOR EOUSLY. o f one atom in
M U L A creases
ELEMENT T E D .TO DETERMIN
E THE OXIDA
TION NUMB
\ . ••1h ER OF AN
e oxidation n
o r each atom umber o f ea~h atom of an el
m H2 , C h , Ss, ement in free
03, P4 , Ca, C, state( uncon~b
etc. ined fo.rm) is zero
.. ·1 h.: n~id . e.g.
ation number •
• :\ lk a li m.:w o f an atom in a
ls have oxidat moi1oatomic io
ion number+ n is equal to it
_.\ lkali ..:arth f-in all their co s charg~.
metals have o mpounds. e.g
.-\ I is t \ ll1sid xidation ·num . NaCl. KCi.
ered to h a v e + ber +2 in all th etc.
3 a~ its oxidat eir compound
ion number in s. e.g.. MgCl:
all its con,pou .C aCO::. etc .
:;_ T h e oxid nds.
ation number •
,•.-:xhibit oxid f i5 -1 in·all its
ation number compoun<ls. T
o f -1 in their he other halog
l Io w e v e r in halid..: compoun ens Cl, Br an
compovnds in ds . e. d I usually
1;rn mlwr o f hP
w hich halogens g . NaCl, NH~Br.
.loge C l, i:3 H F . etc.
co. n h~ve.· ~0s1is.+ 1. e.g ..- BO Cl, ~Ch, aw. e.lt.Ll:i are bonded t<i :,;1;.8 ,m, Q>tiealten M
r and
-L T h e oxid ,l c :\ ~ O Y \ 'l"
\Umbe:r -+ I'
°)O ~ oLve C1C..- ;;
ation number - a.l •-rn t,M.I
o f O is usually :+ 3 , -+ S , + 1 . ', ·J:"
1: :xcrpt in peroxide -2 in all of its
compounds. e.
or peroxide io g. CaO, etc •
Oxidation n n where it !::-is
umb oxid
:t-n· .S ~ e 1 ' er o f O is +2 in OF_2 since !lu~ri ation number of -1. E.g. H iO i
: -, . I h e ,):,; id cl
O.'~..f e.-\ lK
Ot) '. 0 -j .\ d o .tne.0is 1~1ore el_ectronegative. . f
al inn number
1>
0

o f H~tom ,s ei 'Yl' .' Y l~ m b t t'

\\.h1..·n ,·h~ I
I-atom is bond
ed
ther+ I or -1. o t.A ,. r/ z_..
\\ h1..·n ill..: to metals, its oxid
1 I-atom is bonded to a1ion 1hnnber
is .. \ e.g. LiH
non metal~:. ils
oxid.11icH1 n~1m
(,. I 1\1..' ;1 I~1 I ., · . ·ti , o f o ber is +I e.g. C
..· 11 di<.: S 11 xidation num al·I~. H~O
• bers t) I' .1ll lh1:
:, in m s in a ll\
!utrnl molecul
7 1 h1..· ;ii ~1.·hr:11<..:. sl. f tP , idation
l! is /.FRO.
ll ll o • numbe1 ~ nl ' :di lh
l· .11n111s in
a pnl~ at om i< .:
ion is l.'qu.d 1,,
.·1 111
 charge of the ion. c .g. co/· i.e. X +3(-2) = -2

8. The algebraic sum of oxidation numbers of all the atoms in a molecule of a compound is equal
toZERO. e.g. C:1-1 2Ch i.e. X+2(+1)+2(-1)=0

Calculate the oxidation number of the underlined atoms in the foJlowing:-

NalfilQ3 MnO./- ~40/· K 2~◄ NaCN

Calculate oxidation Number of the following:-

l) Mn in Mn203 KMn04 MnO Mn(OH )i

2) N m N02 KN03 NH3 NH.,OH N2 NO

3) S m Na2S-10K sot s, H2S H2SO"

4) Cr tn K2Cr201 Cr(OHh K2Cr04

5) Cl tn HOCI HCI Ch NaCIO•