7373501 electrolysis

8/17/2019 7373501 Electrolysis

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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

http://c/Documents%20and%20Settings/S1313757I/Desktop/formal%20laptop/chem%20bank/Electrolysis/LEAD16.MOVhttp://c/Documents%20and%20Settings/S1313757I/Desktop/formal%20laptop/chem%20bank/Electrolysis/BROMIN16.MOVhttp://c/Documents%20and%20Settings/S1313757I/Desktop/formal%20laptop/chem%20bank/Electrolysis/BROMIN16.MOVhttp://c/Documents%20and%20Settings/S1313757I/Desktop/formal%20laptop/chem%20bank/Electrolysis/LEAD16.MOV


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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 *,


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 *,


At the cathode: )a $ and * $ ions migrate to it.

*$ ions preferentially discharged

due to its lower position in the E(+.

* $ $ e *

http://c/Documents%20and%20Settings/S1313757I/Desktop/formal%20laptop/chem%20bank/Electrolysis/GFORMH16.MOVhttp://c/Documents%20and%20Settings/S1313757I/Desktop/formal%20laptop/chem%20bank/Electrolysis/GFORMH16.MOV


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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 *,


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"

http://c/Documents%20and%20Settings/S1313757I/Desktop/formal%20laptop/chem%20bank/Electrolysis/CLPAPR16.MOVhttp://c/Documents%20and%20Settings/S1313757I/Desktop/formal%20laptop/chem%20bank/Electrolysis/CLPAPR16.MOV


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ectrolysis of co!!er (II) sl!hate solti

Electrolyte:

#ons present:

dilute (u+,- !aq"

(u $ % +,- & from (u+,-



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+,-


'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,