The Reactivity Series and Electrolysis

The reactivity series

The reactivity series ranks metals by how readily they react (how easily they lose electrons to form positive ions). A common order, most to least reactive:

Potassium > Sodium > Lithium > Calcium > Magnesium > Aluminium > (Carbon) > Zinc > Iron > (Hydrogen) > Copper > Silver > Gold

Carbon and hydrogen (non-metals) are included as reference points.

Reactions that show reactivity

• With water: the most reactive metals (Group 1, calcium) react with water → metal hydroxide + hydrogen.
• With acids: reactive metals react with acids → salt + hydrogen (more reactive = faster fizzing). Copper, silver and gold don't react with dilute acids.

Displacement reactions

A more reactive metal will displace a less reactive metal from its compound (e.g. its salt solution).

• Example: iron + copper sulfate → iron sulfate + copper (iron is more reactive, so it takes the sulfate).

Extracting metals

How a metal is extracted depends on its reactivity:

• Metals less reactive than carbon (e.g. iron, copper) can be extracted by reduction with carbon — carbon removes the oxygen. Example: iron oxide + carbon → iron + carbon dioxide.
• Metals more reactive than carbon (e.g. aluminium) must be extracted by electrolysis (carbon can't remove their oxygen).
• Unreactive metals like gold are found native (as the metal itself).

• Oxidation = gain of oxygen (or loss of electrons); Reduction = loss of oxygen (or gain of electrons). Remember OIL RIG: Oxidation Is Loss, Reduction Is Gain (of electrons).

Electrolysis

Electrolysis uses electricity to break down an ionic compound (the electrolyte) into elements. The compound must be molten or dissolved so the ions are free to move.

• Cathode (negative electrode): attracts positive ions (cations) → they gain electrons (reduction). A metal or hydrogen forms here.
• Anode (positive electrode): attracts negative ions (anions) → they lose electrons (oxidation). A non-metal (often oxygen or a halogen) forms here.

Molten example: molten aluminium oxide → aluminium at the cathode, oxygen at the anode. Cryolite is added to lower the melting point and save energy.

Aqueous solutions: at the cathode you get hydrogen unless the metal is less reactive than hydrogen (then the metal forms).

Worked example

Why is aluminium extracted by electrolysis rather than heating with carbon?

• Aluminium is more reactive than carbon, so carbon cannot remove the oxygen from aluminium oxide. Electrolysis is needed instead. ✓

Common mistakes

• Mixing up the electrodes: cathode = negative (attracts positive ions).
• Forgetting displacement needs the added metal to be more reactive.
• Reversing OIL RIG (Oxidation Is Loss of electrons).

Exam tips

• Learn the reactivity order and the carbon/hydrogen reference points.
• State the extraction method based on the metal's position vs carbon.
• For electrolysis, say which product forms at each electrode and why.

Key facts to remember

• Reactivity series ranks metals by how easily they lose electrons; more reactive metals displace less reactive ones.
• Metals below carbon → extracted by reduction with carbon; above carbon → electrolysis.
• Electrolysis: cathode (−) attracts positive ions (metal/H₂); anode (+) attracts negative ions (non-metal); OIL RIG.