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# Reactivity series

## Reactivity of metals

A metal is more reactive than another metal if it loses its electrons more easily. Each metal has a different reactivity.

Potassium, sodium and calcium are highly reactive and will react with cold water. Magnesium, zinc and iron do not react with cold water but will react with steam to form metal oxides.

$$\ce{2K {(s)} + 2H2O {(l)} -> 2KOH {(aq)} + H2 {(g)}}$$ $$\ce{Mg {(s)} + H2O {(g)} -> MgO {(s)} + H2 {(g)}}$$

Lead and all of the metals listed previously react with dilute hydrochloric acid ($\ce{HCl}$) in water to form salts.

$$\ce{Mg {(s)} + 2HCl {(aq)} -> MgCl2 {(aq)} + H2 {(g)}}$$

Copper and silver each have low reactivity and do not react with cold water, steam or dilute hydrochloric acid ($\ce{HCl}$).

## Displacement from aqueous solutions

Metals can displace other metals in solution depending on their positions in the reactivity series.

If metal A is more reactive than metal B, metal A can displace metal B from a solution. Metal A dissolves in solution while metal B solidifies out of solution.

Metal A more easily loses its electrons and thus has a greater tendency to exist as a cation in solution than metal B.

Image of an iron nail that has been immersed in copper (II) sulfate solution for a few days. Iron is higher than copper in the reactivity series. Iron has moved into the solution while copper has deposited on the nail.

When the less reactive metal B is placed in a solution of metal A, it cannot displace metal A from the solution. Hence, no reaction occurs.

## Separating metals from ores

A rock containing iron oxides, haematite and magnetite, as indicated by alternating bands of red and black.

Metals tend to exist in nature as ores. These ores are usually metal oxides, or carbonates. Most pure metals have to be extracted from their ores using suitable chemical methods.

Extraction methods include reduction using carbon or hydrogen and electrolysis.

Metals with low reactivity (copper and silver) can be separated from their ores by reduction with hydrogen or carbon. They lie below carbon and hydrogen in the reactivity series.

Zinc, iron and lead lie below carbon but above hydrogen in the reactivity series. Carbon is more reactive than these metals, and these metals are more reactive than hydrogen.

Ores of these metals can be reduced using carbon but not hydrogen.

Metals above zinc in the reactivity series are difficult to separate by reduction. Potassium, sodium, calcium, magnesium and aluminium are extracted using electrolysis.

## Thermal stability of metal carbonates

Metals form ionic compounds called metal carbonates by combining with carbonate ions ($\ce{CO3^2-}$).

Metal carbonates can be decomposed by heat. However, there are varying degrees of difficulty in decomposing carbonates of different metals.

Thermal stability describes the ease of decomposition. The more thermally stable a compound is, the harder it is to decompose it.

Metals higher in the reactivity series form carbonates with greater thermal stability than those lower in the series. The more reactive a metal is, the greater the stability of the carbonate formed.

Carbonates of highly reactive metals (e.g. potassium and sodium) do not decompose when heated.

Carbonates of less reactive metals decompose when heated. Metal oxides and carbon dioxide are produced in the decomposition reaction.

$$\ce{CuCO3 {(s)} -> CuO {(s)} + CO2 {(g)}}$$
When copper carbonate is heated, carbon dioxide and copper oxide (a black solid) are produced. This can be observed as the solid changes from green to black.