Chlorine dioxide (CIO_2), which is produced by the reaction below, has been test

Question

Chlorine dioxide (CIO_2), which is produced by the reaction below, has been tested as a disinfectant for municipal water treatment. 2 NaCIO_2(aq) + Cl_2(g) rigthtarrow CIO_2(g) + 2 NaCI(aq) Using data from the Standard Reduction Potentials table, calculate E degree, Delta G degree and K at 25 degree C for the production of CIO_2. One of the concerns in using CIO_2 as a disinfectant is that the carcinogenic chlorate ion (CIO_3^- ) might be a by-product. It can be formed from the followin reaction. CIO_2(g) rightarrow CIO_3^-(ag) + Cl^-(aq) Balance the equation for the decomposition of CIO_2. (Use the lowest possible coefficients. Include states-of-matter at 25 degree C and 1 atm in your answer.)

Explanation / Answer

2NaClO2(aq) + Cl2(g) ----> 2 Clo2(g) + 2 NaCl(aq)

E0 = Ecathode - Eanode.

    = (1.36 - 1.19)

    = 0.17 V

DG0 = -nFE0cell

    = -( 2*96500*0.17)

   = -32.81 kj

DG0 = -RTlnK

-32810 = -(8.314*298ln k)

k = 5.64*10^5

b)

    ClO2(aq) ---> ClO3¯(aq) + Cl¯(aq)   [acidic sol.]

Before balancing, allow me to point out the oxidation numbers for the Cl in each compound:

    ClO3¯ (+5)

    Cl¯ (-1)
  
    ClO2 (+4)

Solution #1:

1) Half-reactions:

    ClO2 --> ClO3¯ + e-

    ClO2 + 5e- --> Cl-  

2) Balance them:

    ClO2 + H2O --> ClO3¯ + 2H+ + e-

    ClO2 + 5e- --> Cl- + 2H2O

3) Equalize electrons and combine the half-reactions:

     6ClO2 + 3H2O --> 5ClO3¯ + 10H+ + Cl-

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