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ELECTROLYSIS
CHAPTER 11
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ELECTROLYSIS
The chemical change that takes place when
an electric current passes through a molten or
aqueous electrolyte .
ELECTROLYTE
A compound which when molten or dissolved
in aqueous solution conducts an electriccurrent and is decomposed in the process.
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ELECTRODE
A metal or graphite rod by which thecurrent enters or leaves an electrolyte.
ANODE ( +)
The positive electrode from which electrons
leave the electrolyte.
CATHODE (-)
The negative electrode from which electrons
enter the electrolyte.
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ANION
A negatively charged ion which isattracted to the positively chargedelectrode, the
anode.
CATION
A positively charged ion that isattracted to the negatively chargedelectrode, the cathode.
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Electrolysis of molten lead (II)
bromide
Electrolyte: PbBr !l"
#ons present: Pb $ % Br &
'sing graphite electrodes:
At the cathode: Pb $ $ e Pb
At the anode: Br & Br $ e
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Electrolysis of a binary electrolyte .
Step 1.Break the ionic compound into its ions. X m+ and Y n -
X m+ is call the Cation
Y m- is call the Anion.
Step 2
When the switch is on , the
(ation will mirate to (athode and accept ! electrons "rom the #atter$.
%&eduction occurs'
Anion will mirate to Anode to donate ( electrons %o)idation occurs'
* *lectrol$sis o" molten (aCl
Cathode (a++ e (a or 2(a++ e 2(a
Anode Cl- Cl+ e
r 2Cl- 2Cl+ 2e
ence oerall )a$$ (l& )a $ (l
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Electrolysis of dilte sl!hric acid
Electrolyte: *+,- !aq"% equivalent to acidified water
#ons present: * $ % +,- & from acid
* $ % ,* & from water
'sing platinum electrodes:
At the cathode: * $ ions migrate to it.
* $ $ e *
At the anode: +,- & and ,* & ions migrate to it.
,* & ions preferentially discharged because of its lower
position in the E(+.
- ,* & !aq" *, !l" $ , !g" $ -e
http://c/Documents%20and%20Settings/S1313757I/Desktop/formal%20laptop/chem%20bank/Electrolysis/WATER2.AVIhttp://c/Documents%20and%20Settings/S1313757I/Desktop/formal%20laptop/chem%20bank/Electrolysis/WATER2.AVI
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Electrolysis of dilte sl!hric acid
Note
concentration of acid
increases
products are equia!ent to
t"ose o#tained #$e!ectro!$sis of %ater
o!u&e of o'$en as to" dro en as o#tained is 1 *
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Electrolysis of concentrated hydrochloric aci
Electrolyte:
#ons present:
*(l !aq"
* $ % (l & from *(l
* $ % ,* & from *,
'sing graphite electrodes:
At the cathode: * $ ions migrate to it.
* $ $ e *
At the anode: (l & and ,* & ions migrate to it.
(l & ions preferentially discharged due to higher concentration.
(l & & e (l
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Electrolysis of dilte sodim chloridesoltion
Electrolyte: )a(l !aq"
#ons present: )a $ % (l & from )a(l
*$
% ,*&
from *,
'sing graphite electrodes:
At the cathode: )a $ and * $ ions migrate to it.
*$ ions preferentially discharged
due to its lower position in the E(+.
* $ $ e *
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At the graphite anode: (l & and ,* & ions
migrate to it.
,* & preferentially discharged due to its lower
position in E(+.
- ,* & !aq" *, !l" $ , !g" $ -e
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Electrolysis of concentratedsodim chloride soltion
Electrolyte: )a(l !aq"
#ons present: )a $ % (l & from )a(l
* $ % ,* & from *,
'sing graphite electrodes:
At the cathode: )a $ and * $ ions migrate to it.
*$ ions preferentially dischargeddue to its lower position in the E(+.
* $ $ e *
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If &ercur$ cat"ode is used
"a # and $ # ions migrateto it%
"a # is !referentially
discharged% "a # # e "aThe sodim forms a dilte amalgam &ithmercry%The amalgam is led into iron tan's containing&ater &here it decom!oses to !rodce sodim
hydroide hydrogen and mercry%
)a*g !l" $ *,!l" )a,*!aq" $ *!g" $ *g!l"
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In the indstrial !rocess
unreacted sodiu& c"!oride cr$sta!!ised out !eain#e"ind a concentrated so!ution of sodiu&"$dro'ide,
T"e concentrated sodiu& "$dro'ide so!ution ist"en eaporated to dr$ness to $ie!d sodiu&"$dro'ide pe!!ets,
T"ese pe!!ets are used to &ae soap #$ reaction%it" eeta#!e oi!,
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At the graphite anode: (l & and ,* & ions
migrate to it.
(l & ions preferentially discharged due to higher
concentration.
(l&
& e (l
C"!orine is o#sered as areenis"-$e!!o% as around t"e
anode,
C"!orine is used in t"e&anufacture of #!eac". sodiu&c"!orate (I). # reaction %it"
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ectrolysis of co!!er (II) sl!hate solti
Electrolyte:
#ons present:
dilute (u+,- !aq"
(u $ % +,- & from (u+,-
* $ % ,* & from water
'sing graphite electrodes:
At the cathode: * $ and (u $ ions migrate to it.
(u $ preferentially discharged due to lower position in E(+.
(u $ !aq" $ e (u !s"
(opper is deposited on the electrode as brown copper metal.
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*t the gra!hite anode+
0 +,- & and ,* & ions migrate to it.
0 ,* & preferentially discharged due to its lower position in E(+.
0 ,* & !aq" ,* !g" $ e
0 ,* !g" $ ,* !g" *, !l" $ , !g"0 , !g" $ , !g" , !g"
0 -,* & !aq" *, !l" $ , !g" $ -e
,le color of soltion slo&ly fades de tremoval of C -# ions%
*s $ # and SO. -/ ions remain in the
soltion the reslting soltion is sl!hric
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ctrolysis of co!!er (II) sl!hate soltio
#ons present: (u$
% +,- &
from (u+,-
* $ % ,* & from water
'sing copper electrodes:
At the cathode: * $ and (u $ ions migrate to it.
(u $ preferentially discharged due to lower position in E(+.
(u $ !aq" $ e (u !s"
(opper is deposited on the electrode as brown copper metal.
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*t the co!!er anode+
0 +,-
&
and ,*&
ions migrate to it.
0 since copper is able to lose electrons more easily than +,- &
and ,* & ions% copper anode /dissolves0 to form (u $ ions.
0 (u !s" (u $ !aq" $ e
/or eer$ Cu *+ ion disc"ared at cat"ode.one Cu *+ ion is for&ed at t"e anode,
T"ere is no c"ane in concentration of Cu *+ in so!ution0 so!ution re&ains #!ue t"rou"out,
ass of cat"ode increases. &ass of anode
decreases,