ClO2 is a highly reactive radical that is commonly used in emergency water purif
ID: 922122 • Letter: C
Question
ClO2 is a highly reactive radical that is commonly used in emergency water purification. While ClO2 works well for this application, it is so reactive that it must be generated immediately before use. To do this, a basic solution of ClO2 – and HO2 – is mixed with a solution of 5% phosphoric acid. Upon mixing, the solution changes from colorless to bright yellow.
(a) (2 points) Identify the two half-cell reactions involved in this chemistry. (b) (2 points) Write the balanced chemical equations for the formation of ClO2 under acidic and basic conditions. (c) (2 points) Calculate E° for these two reactions. (d) (2 points) Given this information, comment on role of phosphoric acid in the generation of ClO2. (e) (1 point) Comment on why ClO2 would be a good molecule for water purification.
Explanation / Answer
+1.18
pH = 0:
ClO4-
+1.20
pH = 14:
ClO4-
Chemistry 173a/268a
ClO3-
-0.48
+0.37
ClO3-
ClO2
+1.18
ClO2
+0.30
-0.05
pH = 0:
O3
+2.08
+1.19
+1.66
HClO2
+1.67
+1.07
Cl2
+1.36
Cl-
+0.89
ClO2-
HO2
+0.68
OCl-
+0.42
Cl2
+1.35
Cl-
+1.44
+0.70
O2
+1.63
HOCl
H2O2
+1.76
H2O
+1.23
pH = 14:
-0.03
O3
+1.25
O2
O2-
+0.20
-0.70
HO2-
+0.87
H2O
+0.40