Reactivity Series of Metals

Reactivity Series of Metals

• The reactivity series of metals is a list of metals in order of reactivity based on their reactions with water and acids.
• The series includes metals and non-metals (hydrogen and carbon) and is used to compare the reactivity of different metals.

Reactivity with Cold Water

• The more reactive metals (potassium, sodium, and calcium) react with cold water to form a metal hydroxide and hydrogen gas.
• The reaction is: metal + water → metal hydroxide + hydrogen
• Examples: calcium (Ca + 2H2O → Ca(OH)2 + H2) and potassium (2K + 2H2O → 2KOH + H2)

Reactivity with Steam

• Metals below calcium in the reactivity series react with steam to form a metal oxide and hydrogen gas.
• The reaction is: metal + steam → metal oxide + hydrogen
• Example: magnesium (Mg + H2O → MgO + H2)

Reactivity with Dilute Acids

• Only metals above hydrogen in the reactivity series react with dilute acids.
• The more reactive the metal, the more vigorous the reaction will be.
• Metals that are placed high on the reactivity series (such as potassium and sodium) react explosively with acids.
• The reaction is: metal + acid → salt + hydrogen
• Examples: magnesium (Mg + H2SO4 → MgSO4 + H2) and zinc (Zn + H2SO4 → ZnSO4 + H2)

Reactivity with Oxygen

• Some reactive metals (such as alkali metals) react easily with oxygen.
• The reaction is: metal + oxygen → metal oxide
• Example: copper (2Cu + O2 → 2CuO)

Deducing the Order of Reactivity

• The order of reactivity of metals can be deduced by making experimental observations of reactions between metals and water, acids, and oxygen.
• The more vigorous the reaction of the metal, the higher up the reactivity series the metal is.
• A combination of reactions may be needed to determine the order of reactivity.

Explaining Reactivity

• Metal atoms form positive ions by loss of electrons when they react with other substances.
• The tendency of a metal to lose electrons is a measure of how reactive the metal is.
• A metal that is high up on the series loses electrons easily and is thus more reactive than one which is lower down on the series.

Displacement Reactions

• 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.

Example of Displacement Reaction

• Magnesium + copper sulfate → magnesium sulfate + copper
• Magnesium loses its electrons more easily and the ion of the less reactive metal, copper, will gain these electrons to form elemental copper.

Relative Reactivity Order

• By combining different metals and metal salts solutions, it is possible to come up with a relative reactivity order.
• The order of reactivity of the metals tested can be deduced as: Mg > Zn > Fe > Cu > Ag.

Reactivity of Aluminium

• Aluminium is high in the reactivity series, but in reality, it does not react with water and the reaction with dilute acids can be quite slow.
• This is because it reacts readily with oxygen, forming a protective layer of aluminium oxide which is very thin.
• This layer prevents reaction with water and dilute acids, so aluminium can behave as if it is unreactive.