Question

What reactions take place at the cathode and the anodewhen each of the following is electrolyzed? Assume standard conditions.

a. molten NiBr₂d d. 1.0 M NiBr₂ solution

b. molten AlF₃ e. 1.0 M AIF₃ solution

c. molten Mnl₂ f. 1.0 M Mnl₂ solution

Short answer

Thereactions are as follows:

(a) Reaction when molten NiBr₂ is electrolyzed

Cathode:$N{i}^{2+}+2e^{-}\to Ni$

Anode:$2B{r}^{-}\to B{r}_2+2e^{-}$

(b) Reaction when molten AlF₃ is electrolyzed

Cathode:$A{l}^{3+}+3e^{-}\to Al$

Anode:$2F^{-}\to F_2+2e^{-}$

(c) Reaction when molten MnI₂ is electrolyzed

Cathode:$M{n}^{2+}+2e^{-}\to Mn$

Anode:$2I^{-}\to I_2+2e^{-}$

(d) Reaction when 1.0 M NiBr₂ solution is electrolyzed

Cathode:$N{i}^{2+}+2e^{-}\to Ni$

Anode:$2B{r}^{-}\to B{r}_2+2e^{-}$

(e) Reaction when 1.0 M AlF₃ solution is electrolyzed

Cathode:$2H_{2}O+2e^{-}\to H_2+2O{H}^{-}$

Anode:$2F^{-}\to F_2+2e^{-}$

(f) Reaction when 1.0 M MnI₂ solution is electrolyzed

Cathode:$2H_{2}O+2e^{-}\to H_2+2O{H}^{-}$

Anode:$2I^{-}\to I_2+2e^{-}$

Step-by-step solution

Reaction when molten NiBr2 is electrolyzed

Molten NiBr₂ has two elements Nickel and Bromine. The reaction of reduction for nickel can be denoted as:

$N{i}^{2+}+2e^{-}\to Ni$

The reduction potential is -0.23 V.

The reaction of reduction for bromine can be denoted as:

$B{r}_2+2e^{-}\to 2B{r}^{-}$

The reduction potential is 1.09 V. The reduction potential of bromine is higher than nickel, so the reactions are reduced at the cathode. The reaction at cathode and anode can be denoted as:

Cathode:$N{i}^{2+}+2e^{-}\to Ni$

Anode:$2B{r}^{-}\to B{r}_2+2e^{-}$

Reaction when molten AlF3 is electrolyzed

Molten AlF₃ has two elements Aluminium and Fluorine. The reaction of reduction for aluminium can be denoted as:

$A{l}^{3+}+3e^{-}\to Al$

The reduction potential is -1.66 V.

The reaction of reduction for Fluorine can be denoted as:

$F_2+2e^{-}\to 2F^{-}$

The reduction potential is 2.87 V. The reduction potential of Fluorine is higher than aluminium, so the reaction is reduced at the cathode.

The reaction at cathode and anode can be denoted as:

Cathode:$A{l}^{3+}+3e^{-}\to Al$

Anode:$2F^{-}\to F_2+2e^{-}$

Reaction when molten Mnl2 is electrolyzed

Molten MnI₂ has two elements: manganese and iodine. The reaction of reduction for manganese can be denoted as:

$M{n}^{2+}+2e^{-}\to Mn$

The reduction potential is -1.18 V.

The reaction of reduction for iodine can be denoted as:

$I_2+2e^{-}\to 2I^{-}$

The reduction potential is -0.54 V. The reduction potential of iodine is higher than manganese, so the reaction is reduced at the cathode.

The reaction at cathode and anode can be denoted as:

Cathode:$M{n}^{2+}+2e^{-}\to Mn$

Anode:$2I^{-}\to I_2+2e^{-}$

Reaction when 1.0 M NiBr2 solution is electrolyzed

The reaction of reduction for potassium can be denoted as:

$N{i}^{2+}+2e^{-}\to Ni$

The reduction potential is -0.23 V.

The reaction of reduction for hydrogen gas can be denoted as:

$2H_{2}O+2e^{-}\to H_2+2O{H}^{-}$

The reduction potential is -0.83 V.

The reduction of nickel has higher reduction potential, and the reaction at the cathode can be:

$N{i}^{2+}+2e^{-}\to Ni$

The oxidation reaction for bromine and water to produce oxygen gas can be denoted as:

$2B{r}^{-}\to B{r}_2+2e^{-}$

The reduction potential is 1.087 V.

$2H_{2}O\to O_2+4H^{+}+4e^{-}$

The reduction potential is -1.23 V.

The reaction at cathode and anode can be denoted as:

Cathode:$N{i}^{2+}+2e^{-}\to Ni$

Anode:$2B{r}^{-}\to B{r}_2+2e^{-}$

Reaction when1.0 M AlF3 solution is electrolyzed

The reaction of reduction for aluminium can be denoted as:

$A{l}^{3+}+3e^{-}\to Al$

The reduction potential is -1.66 V.

The reaction of reduction for water can be denoted as:

$2H_{2}O+2e^{-}\to H_2+2O{H}^{-}$

The reduction potential is -0.83 V.

The reduction of water has a higher reduction potential, and the reaction at the cathode can be:

$2H_{2}O+2e^{-}\to H_2+2O{H}^{-}$

The oxidation reaction for Fluorine and water to produce oxygen gas can be denoted as:

$2F^{-}\to F_2+2e^{-}$

The reduction potential is 2.87 V.

$2H_{2}O\to O_2+4H^{+}+4e^{-}$

The reduction potential is -1.23 V.

The oxidation of Fluorine has higher reduction potential, and the reaction at the anode can be:

$2F^{-}\to F_2+2e^{-}$

The reaction at cathode and anode can be denoted as:

Cathode:$2H_{2}O+2e^{-}\to H_2+2O{H}^{-}$

Anode:$2F^{-}\to F_2+2e^{-}$

Reaction when 1.0 M AlF3 solution is electrolyzed

The reaction of reduction for manganese can be denoted as:

$M{n}^{2+}+2e^{-}\to Mn$

The reduction potential is -1.18 V.

The reaction of reduction for hydrogen gas can be denoted as:

$2H_{2}O+2e^{-}\to H_2+2O{H}^{-}$

The reduction potential is -0.83 V.

The reduction of water has a higher reduction potential, and the reaction at the cathode can be:

$2H_{2}O+2e^{-}\to H_2+2O{H}^{-}$

The oxidation reaction for iodine and water to produce oxygen gas can be denoted as:

$I_2+2e^{-}\to 2I^{-}$

The reduction potential is -0.54 V.

$2H_{2}O\to O_2+4H^{+}+4e^{-}$

The reduction potential is -1.23 V.

The oxidation of water to produce from oxygen gas has lower reduction potential, and the reaction at the anode can be:

$2I^{-}\to I_2+2e^{-}$

The reaction at cathode and anode can be denoted as:

Cathode:$2H_{2}O+2e^{-}\to H_2+2O{H}^{-}$

Anode:$2I^{-}\to I_2+2e^{-}$