Electrochemistry in science and technology

SCIENCE IN ACTION

**Corrosion and its control. – Picture from sideplayer.com**

By MICHAEL JOHN UGLO
IN our fourth lecture today we will cover a lesson in electrochemistry.
Without further ado let’s get on with it. Electrochemistry looks at the use of electricity in chemistry to do useful work.
Electricity can be allowed to pass around a circuit due to chemical reactions. Electrochemistry focuses on the redox reactions. Redox simply means red – reduction and ox – oxidation. It is reduction and oxidation reactions.
Anode and cathode
When one part of the circuit which is positive or anodic (anode) is reduced (electrons removed to form ions at anode), the other part which is negative or cathodic (cathode) is oxidised (electrons added to form atoms at cathode).
Electrolysis is the specific term for breaking a compound to form a pure atom of an element in electrochemistry because lysis means to break up something.
Water as we know is made of hydrogen and oxygen atoms. Thus, electrolysis can be used to split the water into hydrogen and oxygen atoms.
A voltage source or battery is used to supply direct current (electricity).
There are two electrodes used. One is the positive electrode called the anode and the other is the negative electrode called the cathode.
The positive terminal of the battery is connected to the anode and negative terminal connected to the cathode. The two electrodes are placed in each side of an aqueous solution called electrolyte.
Electrolytes contain solutions of free ions or charged particles and therefore are also known as ionic solutions.
When the electricity is switched on (or when the electrons are allowed to flow around the circuit or the closed loop), the positive ions migrate to the cathode and the negative ions move to the anode.
The positive ions now flowing to the cathode will gain electrons and become atoms of that ion at the cathode.

**Copper electrolysis Refining Plant. – Picture from copper-recycle.com**

Half reactions
Thus, they are oxidised. When the negative ions flow towards the anode they give away their electrons and form atoms of that ion at the anode. Hence, they are reduced. These reactions are called anodic and cathodic reactions or also called half reactions.
Positively charged ions in electrolytes are also called cations because they migrate to the cathode.
Likewise, negatively charged ions in electrolytes or ionic solutions are called anions because they migrate to the anode.

**Oxidation and reduction reactions. – Picture from youtube.com**

The electrolytes used together with the electrodes are carefully chosen to obtain the result anyone wants to get whether it can be for refining precious metals like gold, silver, copper, nickel in refineries, or electroplating for ornaments like gold plating or silver plating for any jewelries or trophies.
In refineries, the metal to be refined like copper in its impure state (copper ore) is crushed, and smelted allowing the free copper ions in the form of a molten state so when an electric field is applied, the ions can migrate. The anode is a copper electrode and cathode is one electrode that is more electronegative than copper so electric current can flow from the positive (copper) to the negative terminal.
Actually, the electrons flow in the reverse direction (negative to the positive terminal). When the circuit is switched on, copper ions will migrate towards the cathode and in the process accept electrons to form copper atoms the element copper. Thus, there is chemical reaction happening at both the electrodes called the anodic and cathodic reactions or also known as half reactions.

**Combined anodic and cathodic hydrogen production. – Picture from nature.com**

Electroplating
In electroplating, the object to be plated is made the cathode and the metal to be plated with like gold or silver is made the anode. The electrolyte contains the free ions of the metal like gold or silver to be plated like the gold or silver.
When the electric current is switched on, the ions in the electrolytes migrate where by cations move towards the cathode and anions towards the anode.
The cations at the anode accept electrons and become atoms (that is they coat or electroplate the object placed at the cathode. The anions move towards the anode and loose electrons to form the atom of that element. If these are atoms of gaseous elements then, they can covalently bond and be released as gasses of that element.
My Prayer for PNG today is: “You shall sleep, secure in peace. Faithfulness, will be your joy…”

Next week: Metals, non-metals and their compounds.

Michael Uglo is the author of the science textbook “Science in PNG, Pacific, Asia and Caribbean”, and a lecturer in Avionics, Auto-piloting and Aircraft Engineering. Please send comments to: [email protected]