Question

As given in the table below, a student combined 1mL of an aqueous halogen solution with 2mL of dichloromethane, CH₂Cl₂. A few grains of metal or 2mL of halide solution were added to the halogen solution. The solutions were thoroughly mixed and time was allowed for reaction (if any) to go to completion. Complete the following table to summarize the expected observations and conclusions:

Aqueous mixture (with CH2Cl2)	Question 1	Question 2	Question 3	Question 4
Br2 + NaCl
I2 + Zn(s)

1. a) Write the oxidation and reduction half potentials
   b) balanced net ionic equation for overall redox rxn
   c) calculate standard potential for the rxn. written

2. Is the rxn. spontaneous or non-spontaneous?

3. Identify halogen present after the reaction (if any).

4. Color of CH₂Cl₂ layer for each reaction?

Answer 1

FOR THE REACTION BETWEEN Br₂ +NaCl

1) the reduction and oxidation potentials of half reactions are given as below:

$Oxidation half cell:2Br^{-}\rightarrow Br_{2}+2e^{-}...........E^{o}_{op}=-1.09V$

$Reduction half cell:Cl_{2}+2e^{-}\rightarrow 2Cl^{-}...........E^{o}_{rp}=+1.36V$

balanced net equation and cell potential are given as follows:

$Redoxreaction:2Br^{-}+Cl_{2}\rightarrow Br_{2}+2Cl^{-}...........E^{o}_{cell}=+0.27V$

2) since E^o_cell is positive the reaction is spontaneous

3) bromine remains in the solution after the reaction

4) dichloromethane layer shows reddishbrown colour.

FOR THE REACTION BETWEEN I₂ AND Zn

1) the half cell reactions and potentials are given by

$Oxidation half cell:Zn\rightarrow Zn^{+2}+2e^{-}...........E^{o}_{op}=+0.76V$

$Reduction half cell:I_{2}+2e^{-}\rightarrow 2I^{-}...........E^{o}_{rp}=+0.54V$

balanced net equation and cellpotential are given as follows:

$Redoxreaction:Zn+I_{2}\rightarrow Zn^{+2}+2I^{-}...........E^{o}_{cell}=+1.3V$

2) since E^o_cell is positive the reaction is positive

3) none of the halogen remains after the reaction

4) dichlomethanelayer remains colourless