Sri Chaitanya Narayana IIT Academy
Chemistry_Electrochemistry
COMMON CENTRAL OFFICE_MADHAPUR_HYD
CHEMISTRY : ELECTROCHEMISTRY ELECTROCHE MISTRY
Assignment-3 Par agraph f orQuest i onsNos.1t o3 A hydrogen–oxygen fuel cell has a solid electrolyte, which is an ion exchange membrane The membranes is im!ermeable to the reactant gases, but is !ermeable to hydrogen ions, which carry the current between the electrodes To facilitate the o!eration of the cell at "# to $#%C, the electrodes are co&ered with finely di&ided !latinum that function as a catalyst 'ater is drained out of the cell during o!eration (uel cells of this general ty!e ha&e been used successfully in the s!ace !rogram and are )uite efficient Their disad&antages for large– scale commercial a!!lication are that hydrogen !resents storage !roblems, and !latinum is an ex!ensi&e catalyst Chea!er catalysts ha&e been found for higher tem!erature o!eration of hydrogen–oxygen fuel cells (uel cells that use hydrocarbons and air ha&e been de&elo!ed, but their !ower !er unit weight is too low to ma*e them !ractical in ordinary automobiles +etter catalysts are needed A hydrogen–oxygen fuel cell may ha&e an acidic or al*aline electrolyte The half–cell reactions are . ( g ) + / + + e − = / . ( l ) E% 0 - 11 2 − /3 3 e = / ( g ) E% 0 # ––––––––––––––––––––––– –––––––––––––––––––––––––––––––––– ––––––––––––––––––––––– ––––––––––––––––––––––– ––––––––––––––––––––––– ––––––––––––––– ––– / ( g ) + . ( g ) = / . ( l ) E% 0 -112 or . ( g ) + / . ( l ) + e − = ./ − E% 0 #"##4 2 / . ( l ) + e − = / ( g ) + ./ − E% 0 – #154 2 ––––––––––––––––––––––– –––––––––––––––––––––––––––––––––– ––––––––––––––––––––––– ––––––––––––––––––––––– ––––––––––––––––––––––– ––––––––––––––– ––– / ( g ) + . ( g ) = / . ( l ) E% 0 -11 2 To maximi6e the !ower !er unit mass of an electrochemical cell, the electronic and electrolytic resistances of the cell must be minimi6ed Since fused salts ha&e lower electrolytic resistances that a)ueous solutions, high– tem!erature electrochemical cells are of s!ecial interest for !ractical a!!lications /igh tem!erature also allow the use of li)uid metal electrode, which ma*e !ossible higher current densities than solid electrodes -
If 7$# m8 of / gas at ST9 is fed into and is consumed by the fuel cell in -# minutes, then what is the current out!ut of the fuel cell: ;A< "A ;+< 1A ;C< -$A ;=< ;=< -A ° (or a /ydrogen–.xygen fuel cell if ∆/ f ( / ., l ) 0 – 17 *> ? mole, then what will be its
thermodynamic efficiency under standard conditions ;A< #4;+< ;+< #";C< #$@ ;=< ;=< #1@ @
'hy are fuel cells not being used in daily life des!ite their &ery high efficiency ;A< The fuels needed needed for their o!eration o!eration are rarely rarely found in nature nature
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Chemistry_Electrochemistry
;+< Their o!eration always needs &ery high tem!erature ;C< The catalyst used in fuel cells at normal tem!erature are &ery ex!ensi&e ;=
E)ui&alence conductance of saturated solution of +aS." is conductance is
/ence
A< 5)
+<
At
of
and s!ecific
is C<
=<
the EB( of the cell 9b?9bCl??AgCl?Ag is #72 and its tem!erature coefficient is If the heat of formation of
is
A<
+<
C<
=<
The heat of formation of AgCl is,
6)
In acidic medium, Bn. is an oxidant as,
If the !/ of the
solution is decreased by one unit, the electrode !otential of the half cell 9t A< #--1 2 7)
+< #--1 2
for the fuel cell reaction
A< "5"1> -
C< "5"1> -
The heat of solution of anhydrous CuS. " is the heat of hydration of CuS. " +<
=< 75-$> -
and that of C<
is
Calculate
=<
Di&en the data at &alue of log s! for AgI: A<
-#<
at 41 is,
+< @7#> -
A< 9)
=< #@$ 2
Di&en, The
8)
C< #@$ 2
will change by
'hat is the +<
C<
=<
Calculate the e)uilibrium constant for the reaction, (e@3 3 @I− l
(e3 3 I@− The standard
reduction !otentials in acidic conditions are #55 and #7" 2 res!ecti&ely for (e @3 ? (e3 and I@− ? I− cou!les A< 7 ×-#7
+< $$ ×-# −5
C< $$ ×-# 5
=< 7 ×-# −7
Zn + --< A gra!h is !lotted between Ecell and log The cur&e is linier with interce!t on E cell axis e)uals to + Cn --#2 Calculate E cell for the cell Zn ( s ) Zn +
A< -@2 -
( #-M ) Cu + ( ##-M ) cu +< -@2
C< -#52
=< -52
Θ
NO@ → NO ( acidic medium ) E # = #1V concentra Θ
#
NO@ → NH OH ( acidic medium ) E = #5"V C.I98_Chemistry
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Chemistry_Electrochemistry
At what 9/ the abo&e two half reactions will ha&e same EB( &alues : Assume the concentration of all the s!ecies to be unity ;assume ##740##$< A< - +< C< -7 =< -$ Θ
-@
Θ
The standard !otential of O H , Ag O ( s ) Ag , and O H O electrodes are, res!ecti&ely, #"" 2 and #"# 2 at 7# CF for the formation of Ag O, ∆H = −44# J mol −- and may be assumed to be inde!endent of tem!erature Calculate the tem!erature at which Ag O will begin to decom!ose in air ;#G by &olume of . A< −7$ J ? K ? mol +< −"- J ? K ? mol C< −#$" J ? K ? mol =< −-"$ J ? K ? mol
-"
The EB( of the cell Ag AgCl , #-MKCl #-M AgNO@ Ag is #"7 2 #- B Cl is 17G dissociated and #- B AgN. @ is 1G dissocated Calculate the solubuluty !roduct of AgCl at 7# C A< -57 ×-# −-# +< -47 ×-# −4 C< -1 ×-# −4 =< $7 ×-# −-#
-7
Calculate the !otential corres!onding to the following cell gi&en Pt CO
+
( #M ) , CO +@ ( ##-M ) Cr +@ ( #7M ) , CrO5− ( "#M ) , H + (-7M ) Pt
E #CO + ? CO +@ = − -1V E #CrO5 + ? Cr +@ = -@@V F +< #@& C< #@& A< – #"2
=<#-@&
-$
At 7# C , after the addition of --# m8 of #- N NaCl solution to -## m8 of #- N Ag NO@ solution, the reduction !otential of sil&er electrode !laced in it is #@$ 2 Assuming acti&ities to be identical with concentrations, calculate the solubility !roduct of AgCl A< 1 ×-# −-# +< $ ×-# −-# C< -" ×-#−-# =< -5@ ×-# −-#
-5
The standard !otential of OH , Ag O( s ) ? Ag , and OH ? O electrodes are res!ecti&ely #@""2 and #"#2 at 7# C F for the formation of Ag O ∆ H = −44# J mol − and may be assumed be inde!endent of tem!erature Calculate the tem!erature at which Ag O will begin to decom!ose in air ;#G by &olume of O < A< "5#@ K +< @4@#@ K C< "4@#@ K =< @$@#@ K
-1
A staurated calomel electrode is cou!led through a salt bridge with a )uinhydrone electrode di!!ing in #-B NH "Cl The obser&ed EB( at 7# C is #-72 (ind the dissociation constant of NH "OH The oxidation !otential of saturated calomel electrode 0 −#$44V at 7# C A< @ ×-# −7 +< " ×-# −7 C< $ ×-# −7
-4
Calculate the EB( of the cell pt , H ( - atm ) ? CH @COOH ( #-M ) ?? NH "OH ( ##-M ) ? H , Pt ( -atm ) Ka CH COOH = -1 ×-# −7 and K for NH OH = -1 ×-# −7 @ b " A< −#"757 +< +#"757 C< #$757
(
#
=< -1 ×-# −7
)
=< −#$757
A cell Cu ? Cu + ?? Ag + ? Ag initially contains - M Ag + and - M Cu + ions calculate the change in cell !otential after !assage of 4$7A of current for - hr A< E cell decreases by ##-2 +< E cell increases by ##-2
C.I98_Chemistry
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Sri Chaitanya Narayana IIT Academy
Chemistry_Electrochemistry
C< E cell decreases by ##72 -
=< E cell increases by ##72
Batch the following 8ist – I A< Electrode re&ersible wrt cation
!< Pt ? Fe + , Fe +@
+< Electrode re&ersible wrt anion
)< Pt ? H ( -bar ) ? H
C< Hedox Electrode
r< Ag ? AgCl ( s ) , HCl ( aq )
=< Heference electrode
s< Ag ? AgNO@
+
( a = -)
Calculate The minimum wt of Na./ re)uired to be added in H ! to consume all the H ⊕ !resent in H/S Zn ? Zn
of +
cell
of
emf
of
3#5#-2
at
#
7 C
before
its
use
( #-M ) ?? HCl ( -litre ) , H ? Pt ( -atm )
E # = +#5$V Zn ? Zn + A< -$" gm +< $7 gm @
8ist – II
C< -$7 gm
=< @ gm
The e)ui&alent condutance of monobasic acid at infinite dilution is "@1 o"m −-cm If the resisti&ity of the solution containg -7g acid ( M # = "4 ) in -$ is -17 o"mcm what is the degree of disscussion of acid A< "74G
"
C< $#"G
=< 7#5G
Calculate the log K eq for the reaction Zn + Ce +" → Zn + + Ce +@ E # = −#5$V F E # +@ " = − -$-V + Ce ? Ce + Zn ? Zn A< -#-#
7
+< "#G
+< -#-
C< -#4
=< -#1
MnO is .xidised anodically /ow much time is re)uired to oxidise $#1g of MnO by a current of #7A [ At #t Mn = 77] A< 7#-"rs
C.I98_Chemistry
+< "1-"rs
C< $-"rs
=< 7$-"rs
"
Sri Chaitanya Narayana IIT Academy
Chemistry_Electrochemistry
ELECTROCHEMISTRY – 3 EY ! HI"TS -+
=
@C
" +
7A
$+
5+
1+
4+
-# C
--C
-A
-@+
-"A
-7C
-$=
-5A
-1=
-4
#+
A
@+
"A
- A − sF % − r F C − pF & − q
-
Cell reaction + (e;s< + /→
7+
+(e + /
# # # E cell 0 E /+ ,/ − E (e+ ,(e
0 # – ;–#""< 0 3#""2 IsaltJ = 7# 3 log 0 77, ∴ /3J 0 -# –77B !/ 0 ! a 3 log IacidJ K=
@
I(e + J9/ +
I/ J
=
#-×−77
= -#-# F n 0
;-# < ##74 ##74 E cell 0 E #cell − log K = #"" − log-#-# = #-"72 n 7$# Boles of / 0 "## 7$# 4$7## × = 1#" A ∴ Electric current 0 "## $# ×-# ∆D% 0 – n(E% 0 – L 4$7## L -11 >mol –0 – @5-$# *> mol –@5-$ = #1@ Thermodynamic efficiency 0 17
4) Conce!tual 5)
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Sri Chaitanya Narayana IIT Academy
Chemistry_Electrochemistry
6)
7)
8)
;-< ;< Subtracting ;< from ;-<
∴/eat of hydration of 9) A!!lying
-#
--
-
Zn+ Ecell = E cell − log + n Cu + + Ecell = --F Zn = #-MF Cu = ##-M ##74-
+alance both the half &action and a!!ly nernst e)uation −
Put [ NO ] = NO@ = -M in the urt e)uation −
and NO@ = [ NH OH ] = -M in the second e)uation
H Then E- = #1 − #- P → ( -)
E = #5" − ##5 P H → ( )
E- = E ⇒ P H = - -@
(ind ∆' # using ∆' # = − nFE #
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Sri Chaitanya Narayana IIT Academy
Chemistry_Electrochemistry
Then ∆' # = ∆H # − ( ∆ ! #
∴∆! # = −"- J ? mol Ag + anode log -" Ecell = n Ag + cat"ode Ag + anode = #77 × -#−4 M # E cell −
74-
− = #77 × -#−4 K !p = Ag + Cl
-7
(
##74 E E # − log = cell cell $
) ( ##17) = #-5"$ × -#−4 = -57× -#−-#
$ Co +@ Cr + @ $
Co + Cr O − H + 5
-"
= −#@V E cell
-$
Cl −
##74 # log = − E E cell cell K sp
-1
K = ∆H - − - K @#@ ( ( - Conce!tual
-4
= E − E $ E cell
-5
log
#
# − E = E cell cell
-
Conce!tual
##74 n
Cu + log
Ag +
# (ind H ⊕ in H/Electrode using Ecell = E cell −
@
Λm = α = Λ
"
7
-### K m
C ?Λ
#74
Zn + log
H +
= Λ eq
∞
nE #
log K = c ##74 MnO → Mn +5 + @eθ
C.I98_Chemistry
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