METALS & REACTIVITY SERIES

METALS & REACTIVITY SERIES

• The chemistry of the metals is studied by analyzing their reactions with water, dilute acid and air.
• Based on these reactions a reactivity series of metals can be produced
• The series can be used to place a group of metals in order of reactivitybased on the observations of their reactions with water, acid and air.

Carbon and the reactivity series mnemonic

Carbon is an important element and has its own place on the reactivity series

Its use in the extraction of metals from their oxides is discussed in this section but a more complete reactivity series with an accompanying mnemonic to help your memories it is below

The reactivity series mnemonic

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Reactions with Aqueous Ions & Oxides

The reactivity of metals increases going up the reactivity series

This means that a more reactive metal can displace a less reactive metal from its oxide by heating

Example: Copper(II) Oxide

It is possible to reduce copper(II) oxide by heating it with magnesium

As magnesium is above copper in the reactivity series, magnesium is more reactive so can displace copper

The reducing agent in the reaction is magnesium:

CuO (s) + Mg (s) → Cu (s) + MgO (s)

Read also: Experimental Techniques

Other common reactions

Displacement reactions between metals and aqueous solutions of metal salts

Any metal will displace another metal that is below it in the reactivity series from a solution of one of its salts

This is because more reactive metals lose electrons and form ions more readily than less reactive metals, making them better reducing agents

The less reactive metal is a better electron acceptor than the more reactive metal, thus the less reactive metal is reduced. (OIL-RIG: reduction is gain of electrons)

Example: Zinc and copper(II) sulfate

As Zinc is above copper in the reactivity series, zinc is more reactive so can displace copper from copper(II) sulfate solution:

Zn (s) + CuSO₄ (aq) → ZnSO₄ (aq) + Cu (s)

Other Common Reactions

Extended Only

Heating Metal Hydroxides, Carbonates & Nitrates

Thermal decomposition reactions

Some compounds decompose or breakdown when they are heated to sufficiently high temperatures

These reactions are called thermal decomposition reactions

A common example is the thermal decomposition of calcium carbonate (limestone), which occurs at temperatures above 800ºC:

CaCO₃ → CaO + CO₂

Thermal decomposition of metal hydroxides

Most metal hydroxides undergo thermal decomposition

Water and the corresponding metal oxide are the products formed, for example zinc hydroxide thermally decomposes as follows:

Zn(OH)₂ → ZnO + H₂O

Group II metal hydroxides decompose similarly but the Group I hydroxides (apart from lithium) do not decompose due to their having a higher thermal stability

Thermal decomposition of metal carbonates

Most of the metal carbonates and hydrogen carbonates undergo thermal decomposition

The metal oxide and carbon dioxide are the products formed, for example magnesium carbonate thermally decomposes as follows:

MgCO₃ → MgO + CO₂

Group I carbonates (again apart from lithium carbonate) do not decompose when heated

This is due to the high thermal stability of reactive metals; the more reactive the metal then the more difficult it is to decompose its carbonate

CuCO₃ for example is relatively easy to thermally decompose but K₂CO₃ does not decompose.

Thermal decomposition of metal nitrates

All of the metal nitrates decompose when they are heated

Group I nitrates decompose forming the metal nitrite and oxygen, for example sodium nitrate decomposes as follows:

2NaNO₃ → 2NaNO₂ + O₂

Most other metal nitrates form the corresponding metal oxide, nitrogen dioxide and oxygen when heated, for example copper nitrate:

2Cu(NO₃)₂→ 2CuO + 4NO₂ + O₂

Read also: Energy Changes

Aluminum and its apparent lack of reactivity

Aluminum is a curious metal in terms of its reactivity

It is placed high on the reactivity series but it doesn´t react with water or acids

This is because the surface of aluminum metal reacts with oxygen in the air forming a protective coating of aluminum oxide:

4Al + 3O₂ → 2Al₂O₃

The aluminum oxide layer is tough, unreactive, and resistant to corrosion

It adheres very strongly to the aluminum surface and protects it from reaction with other substances, hence making it appear unreactive