Product of Electrolysis

PRODUCTS OF ELECTROLYSIS

ELECTRODE

Electrodes are the material that conducts electricity to or from the cell due to the movement of electrons. The electrode may be a sheet, a wire or a rod. They are of two types –

• ANODE – Positive electrodes are called the Anode. Negatively charged ions move towards the Anode. Oxidation takes place at Anode.

• CATHODE – Negative electrodes are called the cathode. Positively charged ions move towards the cathode. Reduction takes place at the cathode.

ELECTROLYTE

Electrolytes are substances that allow electricity to pass through their aqueous solution or molten state. When electricity is passed through such solutions, the substance present in the electrolyte undergoes chemical decomposition. Electrolytes are generally an aqueous solution of acids, bases and salts. Electrolytes are of two types –

• STRONG ELECTROLYTES – Strong electrolytes that dissociate completely into ions in a solution are strong electrolytes.

• WEAK ELECTROLYTES – Electrolytes that do not dissociate completely into ions in a solution are called weak electrolytes.

ELECTROCHEMICAL CELL

Cells are devices that interconvert electrical energy and chemical energy. A cell consists of the electrolytic solution, salt bridge and electrodes. Cells are basically of two types – ELECTROCHEMICAL CELL and ELECTROLYTIC CELL.

Electrochemical cells are the cells in which chemical energy produced by the redox reactions are used to produce electrical energy. Electrochemical cells are a combination of two half-cells containing the same or different electrodes in the same or different electrolytes. These cells are also called GALVANIC CELL or VOLTAIC CELL. One of the important examples of this type of cell is DANIEL CELL. Salt bridge is only present in an electrochemical cell.

OXIDATION 

Oxidation is the process of removal of an electron in a chemical reaction. Oxidation is the loss of an electron by an atom, ion or molecule. It is also known as de-electronation. Oxidation can also be defined as-

•  Addition of oxygen to an element or compound, or the removal of hydrogen from a compound.

•  Addition of an electronegative element or removal of any other electropositive element.

•  Oxidation involves an increase in oxidation number.

•  An oxidising agent causes oxidation.

             Zn→ Zn+2+ 2 e- 

REDUCTION

Reduction is the process of gain of an electron in a chemical reaction. Reduction is the gain of electrons by an atom, ion or molecule. This process is known as electronation. The reduction can also be defined as-

•  Addition of hydrogen to an element or compound, or the removal of oxygen from a compound.

•  Addition of an electropositive element or removal of any other electronegative element.

• Reduction involves a decrease in oxidation number.

•  A reducing agent causes reduction.

                                 Cu+2 +2 e-→ Cu

ELECTRODE POTENTIAL

When an electrode is in contact with the solution of its own ions in a half-cell, it tends to lose or gain electrons which are known as ELECTRODE POTENTIAL. Electrode potential is expressed in volts. It is independent of the number of species in the reaction. Electrode potential is of two types:

1. OXIDATION POTENTIAL – Oxidation potential is the tendency to lose an electron in a chemical reaction. The oxidation potential of a half cell of an electrochemical cell is inversely proportional to the concentration of ions in the electrolytic solution.

2. REDUCTION POTENTIAL – Reduction potential is the tendency to gain electrons in a chemical reaction. According to IUPAC, the reduction potential can solely be taken as the electrode potential unless specifically mentioned.

ELECTROLYSIS

Electrolysis is the process of decomposition of an electrolytic substance when the electric current is passed through the aqueous solution of electrolyte or molten state of the electrolytic substance.

i) In an electrolytic cell, both oxidation and reduction take place in the same cell.

ii) In an electrolytic cell, Anode is positively charged, and cathode and cathode are negatively charged.

iii) During electrolysis of molten electrolyte, cations (positive ions) are liberated at the cathode, while anions (negative ions) are liberated at the Anode.

iv) If two or more ions are present in the electrolytic solution, the ion with higher reduction potential is liberated at the cathode. In comparison, the ion with lower reduction potential is liberated at the Anode.

Discharge potential is defined as the minimum potential that must be applied across the electrode to bring about the electrolysis and subsequent discharge of ions at the electrodes.

PRODUCTS OF ELECTROLYSIS

The products of electrolysis depend on the type of electrolyte and electrode considered for the redox reaction in an electrochemical cell. Only reactive electrodes take part in the chemical reaction. Inert electrodes do not take part in the chemical reaction. It only works as an electrode catalyst, i.e., platinum electrode. Strong electrolytes undergo faster electrolysis, whereas weak electrolytes require an additional potential to start the chemical reaction. Oxidising and reducing agents also decide the products of electrolysis.

When an aqueous of an electrolyte is electrolysed, if the cation has higher reduction potential than water (-0.83 V), the cation is liberated at the cathode (e.g. in the electrolysis of copper and silver salts); otherwise, hydrogen gas is liberated due to the reduction of water (e.g. in the electrolysis of potassium, sodium, calcium salts, etc.). Similarly, if anion has a higher oxidation potential than water (-1.23 V), the anion is liberated at Anode (e.g. bromide ion); otherwise, oxygen gas is liberated due to oxidation of water (e.g. in the case of fluoride ion, an aqueous solution of sodium sulphate as oxidation potential of sulphate ion is -0.2 V).

CONCLUSION

In electrochemical cells, chemical energy is converted into electrical energy. Electrolysis is the redox reaction taking place in an electrochemical cell and the decomposition of chemical substances at the electrodes. The products of electrolysis depend on the type of electrode and electrolyte considered. On the basis of reduction potential and oxidation potential, the products of electrolysis are varied.