a)If Mn2+ is present in your unknown, it must be reduced from Mn4+ back to Mn2+
ID: 1030857 • Letter: A
Question
a)If Mn2+ is present in your unknown, it must be reduced from Mn4+ back to Mn2+ prior to testing. This is accomplished by adding H202 under acidic conditions. The H202 acts as a reducing agent in acidic solution. The unbalanced net ionic equation for this reaction is: Mn4+(aq) + H2O2(aq) Mn2+(aq) + O2(g) H+ (aq) Balance this equation and write it in the space below: b) Sodium bismuthate is then added to test for the presence of Mn2+. The bisthmutate is added in small portions, as the effervescence may be vigorous if any peroxide is still present, until no further reaction occurs. The bisthmutate ion oxidizes Mn2+ to the purple colored MnO4- ion. The unbalanced net ionic equation for this reaction is: Mn2+(aq) +H+aq) BiO3-(aq) + MnO4 (aq) + Bi3+(aq) Balance this equation and write it in the space below:Explanation / Answer
Mn^4+ (aq) + H2O2(aq) ---------------> Mn^2+ (aq) + O2(g)
O. H. R R. H. R
H2O2 -------------> O2 Mn^4+ (aq) ----------------> Mn^2+ (aq)
H2O2 -------------> O2 +2H^+(aq) Mn^4+ (aq) ----------------> Mn^2+ (aq)
H2O2 -------------> O2 +2H^+(aq) +2e^- Mn^4+ (aq) +2e^- ----------------> Mn^2+ (aq)
H2O2(aq) -------------> O2 +2H^+(aq) +2e^-
Mn^4+ (aq) +2e^- ----------------> Mn^2+ (aq)
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Mn^4+ (aq) + H2O2(aq)--------------> Mn^2+ (aq) + O2 (g) + 2H^+ (aq)
Mn^2+ + BiO3^- (aq) ---------------> MnO4^- (aq) + Bi^3+ (aq)
O. H. R R. H. R
Mn^2+ (aq) -----------> MnO4^- (aq) BiO3^- (aq) --------------> Bi^3+ (aq)
Mn^2+ (aq) +4H2O(l)-----------> MnO4^- (aq) BiO3^- (aq) --------------> Bi^3+ (aq)+ 3H2O(l)
Mn^2+ (aq) +4H2O(l)-------> MnO4^- (aq)+ 8H^+ (aq) BiO3^- (aq) +6H^+ (aq) ------> Bi^3+ (aq)+ 3H2O(l)
Mn^2+ (aq) +4H2O(l)-------> MnO4^- (aq)+ 8H^+ (aq) +5e^- BiO3^- (aq) +6H^+ (aq) +2e^- ------> Bi^3+ (aq)+ 3H2O(l)
2Mn^2+ (aq) +8H2O(l)-------> 2MnO4^- (aq)+ 16H^+ (aq) +10e^-
5 BiO3^- (aq) +30H^+ (aq) +10e^- ------> 5Bi^3+ (aq)+ 15H2O(l)
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2Mn^2+ (aq) + 5BiO3^- (aq) +14 H^+ (aq) --------------> 2MnO4^- (aq) + 5Bi^3+ (aq) +7H2O
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