3.3 Reactivity Series of Metals and Its Application

Reactivity of metals with oxygen
■ Reactions of metals with oxygen

	►	When metals react with oxygen to form metal oxides, redox reactions occur. ○ Metal + oxygen → metal oxide
	►	Metals undergo oxidation as their oxidation number increases.
	►	Oxygen is reduced to oxide ions and the oxidation number decreases from 0 to -2.
	►	Metal acts as a reducing agent and oxygen acts as an oxidising agent.

■ Metal Reactivity Series

	►	Metal arrangement in accordance with the tendency to react with oxygen to form metal oxides.
	►	The more vigorously the metal burns in oxygen, the higher its position in the reactivity series.
	►	Example: ○ Aluminium is more reactive than iron. Thus, aluminium will burn faster in oxygen compare to iron.

■ This video contains information on the reactivity of metals with oxygen

Laboratory Activity 3.3.1: Reactivity of metals with oxygen

Position of carbon in the reactivity series
■ Reactions of carbon with oxygen

	►	When carbon react with oxygen to form carbon dioxide, redox reactions occur. ○ C + O2 → CO2
	►	Carbon undergoes oxidation as the oxidation number increases.
	►	Oxygen is reduced to oxide ions and the oxidation number decreases from 0 to -2.
	►	Carbon acts as a reducing agent and oxygen acts as an oxidising agent.

■ The position for carbon towards oxygen in the reactivity series can be determined by :

	►	Reduction of carbon dioxide by more reactive metal. ○ In this reaction, a strip of burning metal is put in jars filled with carbon dioxide gas ○ If metal is more reactive than carbon, it remains lit with a bright flame producing black fragments (carbon) and white powder. ○ This shows that carbon dioxide can be reduced by metal. ○ Example: ◉ 2Mg + CO2 → 2MgO + C ○ If carbon is more reactive than the metals, no reaction occurs.
	►	Reduction of metal oxide by carbon ○ In this reaction, a mixture of carbon and metal oxide is heated. ○ If carbon is more reactive that the metal, a white flame can be seen. ○ Carbon will act as a reducing agent to reduce metal oxide into metal. ○ Example: ◉ C(s) + 2FeO(s) → 2Fe(s) + CO2(g) ◉ C(s) + 2CuO(s) → 2Cu(s) + CO2(g) ○ If carbon is less reactive than the metals, no reaction occurs.

■ Position of carbon in the reactivity series of metals

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■ This video contains information on the position of carbon in the reactivity series

Laboratory Activity 3.3.2: Position of Carbon in the Reactivity Series

Position of hydrogen in the reactivity series
■ Reactions of hydrogen with oxygen

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When hydrogen burns in oxygen, redox reactions occur. ○ 2H2 + O2 → 2H2O

■ Reactions of hydrogen with oxygen

	►	The position of hydrogen towards oxygen in the reactivity series can be determined by the ability of hydrogen to reduce oxygen from metal oxides.
	►	If hydrogen gas is able to reduce oxygen from the metal oxide to produce metal and water (hydrogen oxide), then hydrogen is more reactive than the metals. ○ Hydrogen + metal oxide → metal + water ○ The hydrogen acts as a reducing agent. ○ Metal oxides which act as oxidising agents oxidize hydrogen to water.
	►	If the hydrogen is below a metal in the series, then it cannot reduce the oxygen in the metal oxides.
	►	The position of hydrogen in the reactivity series of metals:

■ Reaction between metals and water (steam).

	►	Elements that are more reactive compared to hydrogen can reduce water(steam) to hydrogen. ○ Metal + water (steam) → metal oxide + hydrogen
	►	Brief summary of reaction between metal and water (steam). Metal Reaction of metal with water/steam K, Na, Ca Able to react with cold water Mg, Al, Zn, Fe* Can only react with steam Sn, Pb, Cu, Hg, Ag, Au No reaction *Exception: Even though hydrogen is more reactive compared to iron, the reaction between iron and steam can still occur.

■ This video contains information on the position of hydrogen in the reactivity series

Laboratory Activity 3.3.3: Position of Hydrogen in the Reactivity Series

Application of reactivity series
■ The position of a metal in the series determines:

	►	The reactions of the metal with various reagents such as hydrogen and carbon.
	►	The displacement of one metal from its compound by another metal. ○ For example, magnesium is more reactive compare to copper. Therefore magnesium can remove oxygen from the oxide of copper oxide.
	►	The method of extraction of a metal from its ore.

Extraction of metals with carbon
■ Metal ores that exist in the Earth's crust

	►	Most metals are found naturally in compounds form such as oxides, carbonates and sulfides are known as metal ores.
	►	Some examples of metal ores Metal Ore Compound in the ore Chemical formula Aluminium Bauxite Aluminium oxide Al2O3●xH2O Copper Chalcopyrite Copper iron sulphide CuFeS2 Iron Haematite Iron (III) oxide Fe2O3 Iron Magnetite Triferum tetraoxide Fe3O4 Lead Galena Lead sulphide PbS

■ Extraction of metal from their ore with carbon

	►	Carbon is used as a reducing agent in the extraction of metals that are less reactive that carbon.
	►	The extraction method involves the heating of their ores by carbon, in the form of coke.
	►	Carbon is chosen because it is cheaper and readily available.

■ Extraction of tin from their ore

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	►	Tin may contains many impurities such as sand, soil sulphur, carbon and oil.
	►	At first, tin concentrated by flotation. In this process, the ore was crushed and shaken in oily water. Foreign objects such as sand and soil sink while tin attached to the oil and float on the water surface.
	►	Tin then collected and roasted to remove impurities such as carbon, sulfur and oil.
	►	Finally, tin mixed with coke and then heated under high temperature in a furnace.
	►	In the furnace, chemical degradation occurs where tin (IV) oxide is reduced to tin (Sn) by the hot coke according to the equation ◉ SnO2 + 2C → Sn + 2CO ◉ SnO2 + C → Sn + CO2 ◉ SnO2 + 2CO → Sn + 2CO2
	►	Metal tin produced in the molten state and then channeled into molds to produce tin ingots.

■ Extraction of iron from their ore (iron (III) oxide Fe₂O₃)

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	►	A mixture of iron ore (haematite), limestone and coke is fed into a blast furnace.
	►	Hot air (at about 1600°C) flowed into the furnace for burning coke in the mixture. ◉ C + O2 → CO2
	►	Carbon dioxide produced is then reduced by the excess coke to release carbon monoxide (CO). ◉ CO2 + C → 2CO
	►	Carbon monoxide produced in conjunction with excessive coke act as reducing agents reduction iron (III) oxide to iron. ◉ Fe2O3 + 3C → 3Fe + 3CO ◉ Fe2O3 + 3CO → 2Fe + 3CO2
	►	At high temperature, the limestone mixture decomposes to calcium oxide (CaO) and carbon dioxide. ◉ CaCO3 → CaO + CO2
	►	Calcium oxide (CaO) produced then combine with impurities, such as sand (silica, SiO2) to form calcium silicate (CaSiO3) of molten slag which floats on top of the molten iron. Molten iron that accumulates in the bottom of the furnace can then be channeled on the sidelines of a certain time into molds for freezing.

■ This video contains information on the steelmaking.

✍ Worked-example 3.3(a) Choose true or false for the statement given based on the reaction between hydrogen and copper(II) oxide. H2(g) + CuO(s) → Cu(s) + H2O(l) Question Answer Hydrogen is oxidised to water. ✔ Copper(II) oxide is reduced to copper ✔ The oxidation number of hydrogen increases. ✔ The oxidation number of copper decreases. ✔ Hydrogen gas act as the oxidising agent. ✘ Copper(II) ion act as the reducing agent. ✘