Electrolysis
in solutions exercises solution 4
Special note. Marks will be deducted in the exam if equilibrium arrows appear on half equatins at each electrod. The reduction half-equations provided in the electrochemical series include equilibrium arrows because the direction of each half-equation is determined by the combination of oxidant and reductant used in the reaction. Equilibria between an oxidant, its conjugate reductant and electrons are not established at the electrodes.
Students should be aware that oxidation (the loss of electrons) occurs at the anode and reduction (the gain of electrons) occurs at the cathode.

 

 

4) A solution containing a mixture of lead nitrate, magnesium nitrate and silver nitrate was electrolysed. The potential difference across the electrodes was maintained for a long time until bubbles appeared at both electrodes.
a) Predict the products and the order in which they were formed at the anode and the cathode.

b) Give equations for each reaction that took place.

The strongest oxidant and the strongest reductant present will react. The oxidants present are lead (II) ions, Mg(II) ions, Ag ions and water. The only reductant present is water.

So the strongest oxidant is Ag ions will be deposited first followed by lead. Then water will be reduced at the cathode according to the equation below.

 

2H2O(l) + 2e =>H2(g) + 2OH-(aq)

Magnesium will never be deposited as long as water remains.

At the anode water is oxidised according to the equation below.

2H2O(l) => O2(g) + 4H+(aq) + 4e

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Balance for charge by adding electrons tot he most positive side. Balance for hydrogen by adding Hydrogen ions to the hydrogen deficient side. Balance for oxygen by adding water to the oxygen deficient side. Balance for Ag atoms Balance for oxygen by adding water to the oxygen deficient side. Balance for hydrogen by adding Hydrogen ions to the hydrogen deficient side. Balance for charge by adding electrons tot he most positive side. Home
Each oxygen atom has an oxidation number of -2 Reductants in order of increasing strength as we go down the column Oxidants in order of increasing strength as we go up the column.