1.

Balance the following reactions: a. U(SO_(4))_(2)+KMnO_(4)+H_(2)OrarrH_(2)SO_(4)+K_(2)SO_(4)+MNSO_(4)+UO_(2)SO_(4) b. Bi_(2)O_(3)+NaOH+NaOClrarrNaBiO_(3)+NaCl+H_(2)O c. Ca(Ocl)_(2)+KI+HCIrarrI_(2)+CaCl_(2)+H_(2)O+KCI d. MnO+PbO_(2)+HNO_(3)rarrHMnO_(4)+Pb(NO_(3))_(2)+H_(2)O (e) CeI_(3) + KOH + Cl_(20 rarr K_(2)CrO_(3) + KIO_(4) + Kcl+H_(2)O (g) Na_(2)HasO_(3) + NaI + HCl rarr NaCl + KBr + H_(3)AsO_(4) (g) Na_(2)TeO_(3) + Nal rarr NaCl + Te + H_(2)O+I_(2) (h) K_(3)[Fe(CN)_(6)] + Cr_(2)O_(3) + KOH rarr K_(4)[Fe(CN)_(6)]+K_(2)CrO_(4)+H_(2)O (i) NH_(3)+O_(2) rarr NO + H_(2)O (j) HNO_(3)+HI rarr NO + I_(2) + H_(2)O (k) MnSO_(4)+(NH_(4))_(2)S_(2)O_(8) + H_(2)O rarr MnO_(2) + H_(2)SO_(4)+(NH_(4))_(4) (l)CuO+NH_(3)rarrN_(2)+H_(2)O+Cu m. NaHSO_(4)+Al+NaOHrarrNa_(2)S+Al_(2)O_(3)+H_(2)O n. CoCl_(2)+Na_(2)O_(2)+NaOH+H_(2)OrarrCo(OH)_(3)+NaCl o. [Cu(NH_(3))_(4)]Cl_(2)+KCN+H_(2)rarrNH_(3)+NH_(4)Cl+KCl+KCNO+K_(2)Cu(CN)_(3) p. Sb_(2)O_(3)+KIO_(3)+HCI+H_(2)OrarrHSb(OH)_(6)+KCI+ICI q. WO_(3)+SnCl_(2)+HClrarrW_(3)O_(8)+H_(2)SnCl_(6)+H_(2)O r. CoCl_(2)+KNO_(2)+CIrarrK_(3)Co(CNO_(2))_(6)+NO+KCI+H_(2)O s. V(OH)_(4)Cl+FeCl_(2)+HClrarrVOCl_(2)+FeCl_(2)+FeCl_(3)+H_(2)O t. Ag+KCN+O_(2)+H_(2)OrarrK[Ag(CN)_(2)]+KOH u. KClO_(3)+H_(2)SO_(4)rarrKHSO_(4)+O_(2)+ClO_(2)+H_(2)O v. Cr_(2)O_(3)+Na_(2)CO_(3)+KNO_(3)rarrNa_(2)CrO_(4)+CO_(2)+KNO_(2) w. Au+CN^(ө)+O_(2)rarr[Au(CN)_(4)]^(ө) (aqueous solution) x. Zn+ReO_(4)^(ө)rarrRe^(ө)+Zn^(2+) (acidic medium)

Answer»

Solution :a. `U^(4+)(SO_(4)^(2-))_(2)+K^(o+)MnO_(4)^(ө)+H_(2)OSO_(4)^(2-)`
`+(overset(o+)K)SO_(4)^(2-)+MN^(2+)+SO_(4)^(2-)+UO_(2)^(2+)SO_(4)^(2-)`
Reaction is

(Oxidation: `U^(4+)+2H_(2))rarrUO_(2)^(2+)+4H^(o+)+2e^(-)"]"xx5`
(Reduction `10e^(-)+16H^(o+)+MnO_(4)^(ө)rarr2Mn^(2+)+8H_(2)O)`
`ulbar(5U^(4+)+cancel(10overset(2)H_(2)O)+16H^(o+)+2MnO_(4)^(ө)rarr2Mn^(2+)+cancel(8H_(2)O)+5UO_(2)^(2+)+20H^(o))`
or
`5U(SO_(4))_(2)+2H_(2)O+2KMnO_(4)rarr2MnSO_(4)+5UO_(2)SO_(4)+2H_(2)SO_(4)+K_(2)SO_(4)`
b. `Bi_(2)O_(2)+Na^(o+)overset(ө)OH+Na^(o+)OCl^(o+)rarrNa^(o+)Cl^(ө)+H_(2)O+overset(o+)NaBioverset(ө)O_(3)`
Reaction is


Oxidation: `6overset(ө)OH+Bi_(2)O_(3)^(ө)+3H_(2)O+4e^(-)`
Reduction: `2e^(-)+H_(2)O+OCl^(ө)rarrCl^(ө)+2overset(ө)OH"]"xx2`
`ulbar(2OCl^(ө)+2overset(ө)OH+Bi_(2)O_(3)rarr2BiO_(3)^(ө)+H_(2)O+2Cl^(ө))`
or
`ulbar(2NaOCl+2NaOH+Bi_(2)O_(3)rarr2NaBiO_(3)+H_(2)O_NaCl)`
c. `Ca^(2+)(OCl^(ө))_(2)+K^(o+)I^(ө)+H^(o+)Cl^(ө)rarrI_(2)+Ca^(2+)(Cl^(ө))+H_(2)O+K^(o+)Cl^(ө)`
Reaction is

Reduction: `2e^(-)+2H^(o+)+OCl^(ө)rarrCl^(ө)+H_(2)O`
Oxidation `2I^(ө)rarrI_(2)+2e^(-)`
`ulbar(2I^(ө)+2H^(o+)+OCl^(ө)rarrCl^(ө)+H_(2)+I_(2))`
`4KI+4HCl+Ca(OCl)_(2)rarrCaCl_(2)+2H_(2)O+2I_(2)+4KCl`
d. `MnO+PbO_(2)+H^(o+)NO_(3)^(ө)rarrH^(o+)MnO_(4)^(ө)+Pb^(2+)(NO_(3)^(ө))_(2)+H_(2)O`
Reaction is

Oxidation: `3H_(2)O+MnOrarrMnO_(4)^(ө)+5e^(-)+6H^(o+)"]"xx2`
Reduction: `4H^(o+)-2e^(-)+PbO_(2)rarrPb^(2)+2H_(2)O"]"xx5`
`ulbar(2MnO+5PbO_(2)+8H^(o+)rarr2MnO_(4)^(ө)+5Pb^(2+)+4H_(2)O)`
or
`ulbar(2MnO+5PbO_(2)+10HNO_(3)rarr2HMnO_(4)+5Pb(NO_(3))_(2)+4H_(2)O)`
e. `Cr^(3+)(I^(ө))_(3)+K^(o+)OH^(ө)+Cl_(2)rarr(k^(o+))_(2)CrO_(4)^(2-)+K^(o+)IO_(4)^(ө)+K^(o+)Cl^(ө)+H_(2)O`
Note that both `I^(ө)` and `Cr^(3+)` are oxidised to `IO_(4)^(ө)` and `CrO_(4)^(2-)`, respectively, in basic medium.
Oxidation: `[I^(ө)rarrIO_(4)^(ө)]` and `[Cr^(3+)rarrCrO_(4)^(2-)]`
`24overset(ө)OH+12H_(2)O+3I^(ө)rarr3IO_(4)^(ө)+24e^(-)+24H_(2)O`
`3x= -3, 3x-24= -3`
`3x=21`
`8overset(ө)OH+4H_(2)O+Cr^(3+)rarrCrO_(4)^(2-)+3e^(-)+8H_(2)O`
`x=3, x-8= -2`
`x=6`
`ulbar (32overset(ө)OH+CrI_(3)rarr3IO_(4)^(ө)+CrO_(4)^(2-)+16H_(2)O...(i))`
Reduction: `[Cl_(2)rarr2Cl^(ө)]`
`2e^(-)+Cl_(2)rarr2Cl^(ө)`....(ii)
Multiply equation (i) by `2` and equation (ii) by `27` and add to get final redox equation
`ulbar(64overset(ө)OH+2CrI_(3)+27Cl_(2)rarr61O_(4)^(ө)+2CrO_(4)^(2-)+54Cl^(ө)+32H_(2)O)`
or ltbegt `ulbar(64KOH+2CrI_(2)+27Cl_(2)rarr6KIO_(4)+2K_(2)CrO_(4)+54KCl+32H_(2)O)`
f. `(Na)^(o+)HAsO_(3)^(2-)+K^(o+)BrO_(3)^(ө)+H^(o+)Cl^(ө)rarrNa^(o+)Cl^(ө)+K^(o+)Br^(ө)+H_(3)AsO_(4)`
Oxidation `[HAsO_(3)^(2-)rarrH_(3)AsO_(4)]`
`HAsO_(3)^(2-)+H_(2)OrarrH_(3)AsO_(4)+2e^(-)"]"xx3`
N33Reduction `[BrO_(3)^(ө)rarrBr^(ө)]`
`{:(6e^(-)+6H^(o+)+BrO_(3)^(ө)rarrBr^(ө)+3H_(2)O),(ulbar(3HAsO_(3)^(2-)+BrO_(3)^(ө)+6H^(o+)toBr^(ө)+3H_(3)AsO_(4))):}`
g. `(Na^(o+))_(2)TeO_(3)^(2-)+Na^(o+)I^(ө)+H^(o+)Cl^(ө)rarrNa^(o+)Cl^(ө)+Te+H_(2)O+I_(2)`
Oxidation: `[2I^(ө)rarrI_(2)]`
`2I^(ө)rarrI_(2)+cancel(2e^(-))"]"xx2`
Reduction: `[TeO_(3)^(2-)rarrTe]`
`{:(6H^(o+)+cancel(4e^(-))+TeO_(3)^(2-)rarrTe+3H_(2)O),(x-6=-2x=0),(ulbar(4I^(ө)+6H^(o+)+TeO_(3)^(2-)rarr2I_(2)+Te+3H_(2)O)):}`
or
`ulbar(4Nal+6HCl+Na_(2)TeO_(3)rarr2I_(2)+Te+_3H_(2)O+6NaCl)`
h.
Oxidation (basic medium): `[CrO_(3)rarr2CrO_(4)^(2-)]`
`10overset(ө)OH+5H_(2)O+Cr_(3)O_(3)rarr2CrO_(4)^(2-)+cancel(6e^(-))+10H_(2)O`
`2x-6=0, 2x-16=-4`
`2x=6`, `2x=12`
Reduction: `[Fe^(3+)rarrFe^(2+)]`
`{:(ul(e^(-)+[Fe^(3+)(CN)_(6)]^(3-)rarr[Fe^(+2)(CN)_(6)]^(4-)xx6)),(ul(10 overset(ө)OH+6[Fe^(3+)(CN)_(6)]^(3-)+Cr_(2)O_(3)0gt6[Fe(CN)_(6)]^(4-)+2CrO_(4)^(2-)+5H_(2)O)),(overset(or)ul(10KOH+6K_(3)[Fe(CN)_(6)]+Cr_(2)O_(3)rarr6K_(4)[Fe(CN)_(6)]+2K_(2)CrO_(4)+5H_(2)O)):}`
i. Oxidation: `[NH_(3)rarrNO]`
`H_(2)O+NH_(3)rarrNO+cancel(5e^(-))+cancel(5H^(o+))"]"xx4`
`x+3=0, x-2=0`
`x= -3, x=2`
Reduction: `[O_(2)rarr2H_(2)O]`
`{:(cancel(4H^(o+))+cancel(5e^(-))+O_(2)rarr2H_(2)O"]"xx5),(2x=04+2x=0),(2x= -4),(ulbar(4NH_(3)+5O_(2)rarr4NO+6H_(2)O)):}`
j. `H^(o+)NO_(3)^(ө)+H^(o+)I^(ө)rarrNO+I_(2)+H_(2)O`
Oxidation `[2I^(ө)rarrI_(2)]:`
`2I^(ө)rarrI_(2)+cancel(2e^(-))"]"xx3`
Reduction `[NO_(3)rarrNO]`
`{:(4H^(o+)+cancel(3e^(-))+NO_(3)^(ө)rarrNO+2H_(2)O"]"xx2),(x-6= -1 x-2=0),(x=5 x=2),(ulbar(6I^(ө)+8H^(o+)+2NO_(3)^(ө)rarr2NO+3I_(2)+4H_(2)O)),(overset(or)6HI+2HNO_(3)rarr2NO+3I_(2)+4H_(2)):}`
`Mn^(2+)SO_(4)^(2-)(overset(o+)NH_(4))_(2)S_(2)O_(8)^(2-)+H_(2)OrarrMnO_(2)`
`+(H^(o+))_(2)SO_(4)^(2-)+(overset(o+)NH_(4))_(2)SO_(4)^(2-)`
Oxidation: `[Mn^(2+)rarrMnO_(2)]`
`2H_(2)O+Mn^(2+)rarroverset(+4)MnO_(2)+cancel(2e^(-))+4^(o+)`
Reduction" `[S_(2)O_(8)^(2-)rarr2SO_(4)^(2-)]`
`{:(cancel(2e^(-))+S_(2)O_(8)^(2-)rarr2SO_(2)^(2-)),(ulbar(2H_(2)O+Mn^(2+)+S_(2)O_(8)^(2-)rarrMnO_(2)+4H^(o+)+2SO_(4)^(2-))),(overset(or)ulbar(2H_(2)+MnSO_(4)+(NH_(4))_(2)S_(2)O_(8)rarrMnO_(2)+2H_(2)SO_(4)+(NH_(4))_(2)SO_(4))):}`
l. Oxidation : `[2NH_(3)rarrN_(2)]`
`2NH_(3)rarrN_(2)+cancel(6e^(-))+cancel(6H^(o+))`2x+6=0`
, `2x=0`
`2x= -6`
Reduction : `[CuOrarrCu]`
Reduction: `[CuOrarrCu]`
`{:(2H^(o+)+cancel(2e^(-))+CuOrarrCu+H_(2)O"]"xx3),(ulbar(2NH_(3)+3CuOrarrN_(2)3Cu+3H_(2)O)):}`
m. Oxidation (basic medium): `[2AlrarrAl_(2)O_(3)]`
`6overset(ө)OH+3H_(2)O+2AlrarrAl_(2)O_(3)+6e^(-)+6H_(2)O"]"xx4`
Reduction: `[HSO_(4)^(ө)rarrS^(2-)]`
`{:(7H_(2)P+cancel(8e^(-))+HSO_(4)^(ө)rarrS^(2-)+4H_(2)O+7overset(ө)OH"]"xx3),(ulbar(3overset(ө)OH+8Al+3HSO_(4)^(ө)rarr4Al_(2)O_(3)+3H_(2)O+3S^(2-))),(or),(ulbar(3NaOH+8Al+3NaHSO_(4)rarr4Al_(2)O_(3)+3H_(2)O+3Na_(2)S)):}`
n. `Co^(2+)(Cl_(2)^(ө))+Na_(2)O_(2)+Naoverset(ө)OH+H_(2)OrarrCo(OH)_(3)+Na^(o+)Cl^(ө)`
Oxidation (basic method): `[Co^(2+)rarrCo(OH)_(3)]`
`3overset(ө)OH+cancel(3H_(2)O)+Co^(2+)rarrCo(OH)_(3)+cancel(e^(-))++cancel(3H_(2)O)"]"xx2`
Reduction: `[O_(2)^(-2)rarr2overset(ө)OH]`
`{:(2H_(2)O+cancel(2e^(-))+O_(2)^(2-)+2overset(ө)OH),(ulbar(4overset(ө)OH+2Co^(2+)+2H_(2)O+O_(2)^(2-)rarr2Co(OH)_(3))),(or),(ulbar(2NaOH+2CoCl_(2)+2H_(2)O+Na_(2)O_(2)rarr2Co(OH)_(3)+4NaCl)):}`
o. `Cu(NH_(3))_(2)^(2+)(Cl^(ө))_(2)+K^(o+)CN^(ө)+H_(2)OrarrNH_(3)+overset(o+)NH_(4)Cl^(ө)`
`+(K^(o+))_(2)Cu(CN)_(3)^(2-)+K^(o+)CNO^(ө)+K^(o+)Cl^(ө)`
Oxidation (basic `NH_(3)`medium): `[CN^(ө)rarrCNO^(ө)]`
`
Since the reaction is CARRIED out in `NH_(3)` medium, add `2NH_(3)` to both sides.
`2NH_(3) + H_(2)O + CN^(Ө) rarr CNO^(Ө) + 2e^(-)+2NH_(4)^(o+)`...(i)
Reduction: `[Cu^(2+) rarrCu^(1+)]` (bacis `NH_(3)` medium)
`e^(-) + Cu^(2+) rarrCu^(1+)`
Add `4NH_(3)` and `3CN^(Ө)` to both sides:
`e^(-) + Cu^(2+) + 4NH_(3) + 3CN^(Ө) rarr Cu^(+1) + 4NH_(3) + 3CN^(Ө)`
or
`e^(-) + Cu(NH_(3))_(4)^(2+) + 3CN^(Ө) rarr Cu(CN)_(3)^(2-) + 4NH_(3)`
or
`2e^(-) + 2Cu(NH_(3))_(4)^(2+)+6CN^(Ө) rarr 2Cu(CN)_(3)^(2-) + 8NH_(3)`....(ii)
Add equations (i) and (ii)
`H_(2)O+7CN^(Ө) + 2Cu(NH_(3))_(4)^(2+) rarr 2Cu(CN)_(3)^(2-)+CNO^(Ө) + 6NH_(3) + overset(o+)(2NH_(4))` ltbr. Net redox reaction is
`H_(2)O+7KCN+2Cu(NH_(3))Cl_(2)-2K_(2)Cu(CN)_(3)`
`+KCNO+6NH_(3)+2NH_(4)Cl+2KCl`
p.
Oxidation `[Sb_(2)O_(3)rarr2HSb(OH)_(6)]`
`{:(9H_(2)O+Sb_(2)O_(3)rarr2HSb(OH)_(6)+cancel(4e^(-))+4H^(o+),,,,),(2x-6=0 2+2x-12=0,,,,),(2x=6 2x=10,,,,):}`
Reduction `[IO_(3)^(Ө)rarrI^(o+)]`
`{:(6H^(o+)+4e^(-)+IO_(3)^(Ө)rarrI^(o+)+3H_(2)O,,,,),(x-6=-1 x=1,,,,),(x=5,,,,):}`
`{:(ulbar(6H_(2)O+2H^(o+)+Sb_(2)O_(3)+IO_(3)^(o+)rarr2HSb(OH)_(6)+I^(o+))),(or),(ulbar(6H_(2)O+2HCl+Sb_(2)O_(3)+KIO_(3)rarr2HSb(OH)_(6)+ICl+KCl)):}`
q. `WO_(3)+Sn^(2+)(Cl^(Ө))_(2)+H^(o+)Cl^(Ө)rarrW_(3)O_(8)+(H^(o+))_(2)SnCl_(6)^(2-)+H_(2)O`
Oxidation: `[Sn^(2+)rarrSnCl_(6)^(2-)]`
``{:(Sn^(2+)rarrSn^(4+)+2e^(-)),(ulbar(6Cl^(Ө)+Sn^(2+)rarrSnCl_(6)^(2-)+Sn^(4+)+cancel(2e^(-)))):}`
Reduction: `[3WO_(3)rarrW_(3)O_(8)]`
`{:(2H^(o+)+cancel(2e^(-))+3WO_(3)rarrW_(3)O_(8)+H_(2)O`,,,,),(3x-18=0 3x-16=0,,,,),(3x=18 3x=16,,,,):}`
`{:(ulbar(2H^(o+)+6Cl^(o+)+3WO_(3)+Sn^(2+)rarrSnCl_(6)^(2-)+W_(3)O_(8)+H_(2)O)),(or),(ulbar(4HCl+3WO_(3)+SnCl_(2)rarrH_(2)SnCl_(6)+W_(3)O_(8)+H_(2)O)):}`
r. `Co^(2+)(Cl^(Ө))_(2)+K^(o+)NO_(2)^(Ө)+H^(o+)Cl^(Ө)rarr(K^(o+))_(3)Co^(3+)(NO_(2))_(6)^(3-)+NO+K^(o+)Cl^(Ө)+H_(2)O`
Oxidation: `[Co^(2+)0gtCo^(3+)]`
`Co^(2+)rarrCo^(3+)+cancel(e^(-))`
or `6NO_(2)^(Ө)+Co^(2+)rarrCo(NO_(2))_(6)^(3-)+cancel(e^(-))`
Reduction: `[NO_(2)^(Ө)rarrNO]`
`{:(2H^(o+)+cancel(2e^(-))+NO_(2)^(Ө)rarrNO+H_(2)O),(ulbar(2H^(o+)+7KNO_(2)^(Ө)+Co^(2+)rarrCo(NO_(2))_(6)^(3-)+NO+H_(2)O)),(or),(ulbar(2HCl+7KNO_(2)+CoCl_(2)rarrK_(2)Co(NO_(2))_(6)+NO+H_(2)O+4KCl)):}`
s. `V(OH)_(4)`^(o+)Cl^(Ө)+Fe^(2+)(Cl^(Ө))_(2)+H^(o+)Cl^(Ө)rarrVO^(2+)(Cl^(Ө))_(2)+Fe^(3+)(Cl^(Ө))_(3)+H_(2)O`
Oxidation: `[Fe^(2+)rarrFe^(3+)]`
Fe^(2+)rarrFe^(+3)+cancel(e^(-))`
Reduction": `[V(OH)_(4)^(o+)rarrVO^(2+)]`
{:(2H^(o+)+cancel(e^(-))+V(OH)_(4)^(o+)rarrVO^(2+)+3H_(2)O),(ulbar(2H^(o+)+Fe^(2+)+V(OH)_(4)^(o+)rarrVO^(2+)+Fe^(3+)+3H_(2)O)),(or),(ulbar(2HCl+FeCl_(2)+V(OH)_(4)ClrarrVOCl_(2)+FeCl_(3)+3H_(2)O)):}`
t. `Ag+K^(o+)CN^(Ө)+O_(2)+H_(2)OrarrK^(o+)Ag(CN)_(2)^(Ө)+K^(o+)overset(Ө)OH`
Oxidation: `[AgrarrAg^(o+)]`
`AgrarrAg^(o+)+e^(-)`
`Ag+2CN^(Ө)rarrAg(CN)_(2)^(Ө)+cancel(e^(-))"]"xx4`
reduction: [`O_(2)rarroverset(Ө)OH]` (Basic medium)
``{:({:(2H_(2)O+cancel(4e^(-))+O_(2)rarr2overset(Ө)OH+2overset(Ө)OH,,,,),(2x=0 2x=-4,,,,),(2x=-4,,,,):}),(ulbar(4Ag+8CN^(Ө)+2H_(2)O+O_(2)rarr4Ag(CN)_(2)^(Ө)+4overset(Ө)OH)),(or),(ulbar(4Ag+8KCN+2H_(2)O+O_(2)rarr4KAg(CN)_(2)+4KOH)):}`
u.
Oxidation `[3O^(2-)rarr(3)/(2)O_(2)+6e^(-)]`
Reduction `[e^(-)+overset(+5)(ClO_(3)^(Ө))rarroverset(+4)(ClO_(2))]`
`{:(4KClO_(3)rarrO_(2)+4ClO_(2)),(ulbar(4H_(2)SO_(4)+4KClO_(3)rarr4KHSO_(4)+O_(2)+4ClO_(2)+2H_(2)O)):}`

Oxidation `[Cr_(2)O_(3)rarrCrO_(4)^(2-)]`
`{(5H_(2)O+Cr_(2)O_(3)rarr2CrO_(4)^(2-)+cancel(6e^(-))+10H^(o+),,,,),(2x-6=0 2x-6= -4,,,,),(2x=6 2x=12,,,,):}`
Reduction:`[NO_(3)^(Ө)rarrNO_(2)^(Ө)]`
`{:(2H^(o+)+cancel(2^(-))+NO_(3)^(Ө)rarrNO_(2)^(Ө)+H_(2)O"]"xx3),(ulbar(2H_(2)O+Cr_(2)O_(3)+3NO_(3)^(Ө)rarr2CrO_(4)^(2-)+3NO_(2)^(Ө)+4H^(o+))):}`
Add `3K^(o+) and `4Na^(o+)` ions to both sides.
`2H_(2)O+Cr_(2)O_(3)+3KNO_(3)+4na^(o+)rarr2Na_(2)+CrO_(4)+3KNO_(3)+4H^(o+)`
[Now add `2H_(2)CO_(3)` to the lerft and `2CO_(2)+2H_(2)O` to the right of the equation]
`[4H^(o+)+2CO_(3)^(2-)-=2CO_(2)+2H_(2)O]`
`cancel(2H_(2)O)+Cr_(2)O_(3)+3KNO_(3)+4Na^(o+)+2H_(2)CO_(3)rarr`
`2Na_(2)CrO_(4)+3KNO_(3)+4H^(o+)+2CO_(2)+cancel(2H_(2)O)`
or `Cr_(2)O_(3)+3KNO_(3)+2Na_(2)CO_(3)+cancel(4H^(o+))rarr2Na_(2)CrO_(4)`
`+3KNO_(3)+2CO_(2)+cancel(4H^(o+))`
Hence, the net redox reaction is
`ulbar(Cr_(2)+3KNO_(3)+2Na_(2)CO_(3)rarr2Na_(2)CrO_(4)+3KNO_(3)+2CO_(2)`
w. `Au+CN^(Ө)+O_(2)rarrAu^(3+)(CN)_(4)^(Ө)`
`CN^(Ө)` must be kept out of acid solution)
Oxidation: `[AurarrAu^(3+)]`
Add `4CN^(Ө)` both sides
`4CN^(Ө)+AurarrAu(CN)_(4)^(Ө)+cancel(3e^(-))"]"xx4`
Reduction: `[O_(2)rarroverset(Ө)OH]`
`{:({:(2H_(2)O+cancel(4e^(-))+O_(2)rarr2overset(Ө)OH+2overset(Ө)OH"]"xx3,,,,),(2x=0 2x+2= -2,,,,),(2x=4,,,,):}),(ulbar(4Au+16CN^(Ө)+6H_(2)+3O_(2)rarr4Au(CN)_(4)^(Ө)+12overset(Ө)OH)),(or),(ulbar(4Au+16CN+6H_(2)O+3O_(2)rarr4KAu(CN)_(4)+12KOH)):}`
x. Oxidation: `[ZnrarrZn^(2+)]`
`Zn+Zn^(2+)+2e^(-)"]"xx4`
Reduction: `[ReO_(4)^(Ө)rarrRe^(Ө)]`
`{:({:(8H^(o+)+8e^(-)+ReO_(4)^(Ө)+4H_(2)O,,,,),(x-8=-1 x= -1,,,,),(x=7,,,,):}),(ulbar(4Zn+8H^(o+)+ReO_(4)^(Ө)rarr4Zn^(2+)+Re^(Ө)+4H_(2)O)):}`


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