How Highly Reactive Metals Are Extracted Using Electrolysis with Reactions and Examples
Activity series of elements at the top of the series include potassium (K), sodium (Na), calcium (Ca), Magnesium (Mg) and others. Metals at the peak of the reactivity range cannot be produced from their compounds via carbon (C) reduction. This happens because metals have a higher affinity for oxygen (O2) over carbon (C), making them more reactive.
Metals near the peak of the reactivity range are thus obtained through the electrolysis of corresponding molten chlorides (Cl-). When an electric current is conducted over molten sodium (Na) metal, positive ions are created at the cathode (oxidising or positive electrode). Consequently, chloride ions, which are negative ions, were deposited in the type of chlorine at the anode (reducing or negative electrode). This method is known as electrolytic reduction. Metals extracted through electrolytic reduction are pure.
In this article, let’s understand more about activity series and extracting metals towards the top of the activity series using certain examples and its reaction.
What is an Activity Series?
The periodic table's reactivity is determined by the reactivity series, often referred to as the activity series. This series is structured to ensure that the highly reactive metal falls prior and on top of the least reactive metal.
The activity series of metals listed in decreasing sequence of activity. Upon displacement studies, the accompanying series, referred to as the activity or reactivity series was generated.
Extraction of Sodium (Na) Metal from Sodium Chloride (NaCl)
Molten sodium chloride (NaCl) releases sodium (Na+) metal at the cathode and chlorine (Cl-) at the anode when an electric current is applied to it.
\[N{a^ + } + {e^ - } \to Na\]
\[2C{l^ - } \to C{l_2}\left( g \right) + 2{e^ - }\]
\[2NaCl\left( {molten} \right) \to 2Na\left( s \right) + C{l_2}\left( g \right)\]
The only way to get sodium (Na) metal is by melting sodium chloride (NaCl), not by dissolving it in water. This is because sodium (Na) metal accumulated at the cathode combines with water contained in the solution to generate sodium hydroxide (NaOH) when an electric current is transmitted through an aqueous solution of sodium chloride (NaCl).
\[4Na + 2{H_2}O \to 4NaOH\]
Extraction of Aluminum (Al) Metal from Aluminium Oxide (Al2O3)
In a manner similar to how sodium (Na) metal is removed, aluminium metal is reduced electrolytically. The positively charged aluminium (Al) ion is drawn to the cathode when an electric current is run through the molten aluminium oxide. Aluminum (Al) metal is created at the cathode when the aluminium (Al) ion receives electrons from the cathode.
However, because they had a negative charge, oxide ions were attracted to the anode. Oxide ions lose their electrons at the anode, forming oxygen gas.
\[A{l^{ + + + }} + 3{e^ - } \to Al\]
\[2{O^{ - - }} \to {O_2}\left( g \right) + 4{e^ - }\]
\[2A{l_2}{O_3} \to 4Al\left( s \right) + {O_2}\left( g \right)\]
Metal Refining
With the exception of those acquired through electrolytic reduction, metals obtained through various extraction procedures all contain a variety of contaminants. In order to produce pure metals, impure metals acquired through various processes are refined.
Interesting Facts
The most reactive activity series of metals potentially react in the presence of air or moisture. These metals include calcium, sodium, and potassium.
Copper and silver, the metals at the bottom of the activity series, can also be found together in their sulphide or oxide ores.
The oxides, sulphides, and carbonates that make up the majority of the earth's crust are composed of the metals in the middle of the activity series.
Impure metals can be refined using a variety of techniques, however electrolytic refining is among the quite used ones.
Several metals are refined electrically, including copper, zinc, silver, gold, etc.
Key Features to Remember
Metals towards the top of the activity (or) reactivity series have a high level of reactivity. By heating with carbon, they cannot be extracted from their compounds.
Carbon, for instance, is unable to convert the oxides of sodium (Na), magnesium (Mg), calcium (Ca), aluminium (Al), etc. into the corresponding metals. This is due to the fact that certain metals are more apt to bind oxygen than carbon.
Extracting metals towards the top of the activity series can be obtained mainly through electrolytic reduction.
Most of the time metals extracted through electrolytic reduction will be in pure form.
FAQs on Extracting Metals Towards the Top of the Activity Series in Chemistry
1. What does extracting metals towards the top of the activity series mean?
Extracting metals towards the top of the activity series means obtaining highly reactive metals that cannot be reduced by carbon and are usually extracted by electrolysis.
- Metals such as potassium, sodium, calcium, magnesium, and aluminium are at the top of the reactivity (activity) series.
- They form very stable compounds like oxides and chlorides.
- Because they are more reactive than carbon, they must be extracted using electrolytic reduction of molten compounds.
2. Why can’t metals at the top of the activity series be extracted by carbon reduction?
Metals at the top of the activity series cannot be extracted by carbon reduction because they are more reactive than carbon.
- Carbon can only reduce oxides of metals that are less reactive than itself.
- Highly reactive metals like sodium and magnesium form very stable oxides.
- Carbon cannot remove oxygen from these oxides, so electrolysis is required instead.
3. How is sodium extracted from its ore?
Sodium is extracted by the electrolysis of molten sodium chloride (NaCl) in a Down’s cell.
- The electrolyte used is molten NaCl(l).
- At the cathode: Na+(l) + e- → Na(l)
- At the anode: 2Cl-(l) → Cl2(g) + 2e-
- Overall reaction: 2NaCl(l) → 2Na(l) + Cl2(g)
4. How is aluminium extracted from bauxite?
Aluminium is extracted from bauxite by the electrolysis of molten aluminium oxide (Al2O3) in the Hall–Héroult process.
- Bauxite is purified to obtain Al2O3.
- Aluminium oxide is dissolved in molten cryolite (Na3AlF6) to lower its melting point.
- Overall reaction: 2Al2O3(l) → 4Al(l) + 3O2(g)
5. What is the activity series in metal extraction?
The activity series is a list of metals arranged in order of decreasing reactivity, which helps predict their method of extraction.
- Top: K, Na, Ca, Mg, Al (very reactive).
- Middle: Zn, Fe, Pb (moderately reactive).
- Bottom: Cu, Ag, Au (least reactive).
- Metals above carbon require electrolysis for extraction.
6. What is electrolysis in the extraction of reactive metals?
Electrolysis is the process of using electric current to decompose molten ionic compounds to extract reactive metals.
- The compound must be in molten state so ions are free to move.
- Reduction occurs at the cathode (gain of electrons).
- Oxidation occurs at the anode (loss of electrons).
- Example: MgCl2(l) → Mg(l) + Cl2(g)
7. Can magnesium be extracted by electrolysis?
Yes, magnesium is extracted by the electrolysis of molten magnesium chloride (MgCl2).
- At the cathode: Mg2+(l) + 2e- → Mg(l)
- At the anode: 2Cl-(l) → Cl2(g) + 2e-
- Overall reaction: MgCl2(l) → Mg(l) + Cl2(g)
8. Why are molten compounds used instead of aqueous solutions in extracting reactive metals?
Molten compounds are used because in aqueous solutions, water is reduced instead of the highly reactive metal ions.
- Reactive metals like sodium and calcium react with water.
- In aqueous electrolysis, hydrogen gas forms at the cathode instead of the metal.
- Using molten salts ensures only metal ions are reduced.
9. What are examples of metals extracted by electrolysis?
Examples of metals extracted by electrolysis include potassium, sodium, calcium, magnesium, and aluminium.
- Na from molten NaCl.
- Mg from molten MgCl2.
- Al from molten Al2O3.
- All are highly reactive metals above carbon in the activity series.
10. What are the key differences between electrolysis and carbon reduction in metal extraction?
The key difference is that electrolysis uses electricity to extract highly reactive metals, while carbon reduction uses carbon to extract less reactive metals.
- Electrolysis: Used for metals above carbon (e.g., Na, Mg, Al).
- Carbon reduction: Used for metals below carbon (e.g., Fe, Zn).
- Example of carbon reduction: Fe2O3(s) + 3CO(g) → 2Fe(l) + 3CO2(g)
