Extraction of alkali metals: an introduction to redox chemistry
The principle sources for Na and Okay are rock salts. Each parts don’t naturally happen of their elemental state. In
distinction, Li, Rb and Cs have small pure abundances, but in addition happen as rock salts. As beforehand talked about,
solely synthetic isotopes of Fr are recognized.
Sodium is manufactured by the so-called Downs’ course of, which is the electrolysis of molten NaCl and
represents the key manufacturing course of for sodium steel and can also be a minor supply of business chlorine.
The method is predicated on a redox response (see Part 2.1.2) the place the discount of liquid Na+ to liquid Na
takes place on the cathode and the oxidation of liquid chloride (Cl−) to chlorine (Cl2) gasoline on the anode:
Discount on the cathode ∶ Na+
(l) + e− → Na(l)
Oxidation on the anode ∶ 2Cl−
(l) → Cl2(g) + 2e−
General redox response ∶ 2Na+
(l) + 2Cl−
(l) → 2Na(l) + Cl2(g)
Molten NaCl is used because the electrolyte medium throughout the electrolytic Downs’ course of and CaCl2 is added
as a way to lower the working temperature. The melting level of NaCl is 800 ∘C, whereas the addition of
CaCl2 lowers it to round 600 ∘C. The design of the electrolysis cell is essential as a way to forestall oxidation
and hydrolysis of freshly produced sodium and recombination to NaCl. Chlorine (Cl2) is produced on the
Alkali Metals 21
Determine 2.2 Schematic diagram of Down’s cell
constructive graphite anode and captured in type of gasoline, whereas Na+ is lowered to liquid sodium on the detrimental
iron cathode and picked up in its liquid type.
The anode is outlined because the electrode at which the oxidation takes place, which, means on this instance, that
the anode is positively charged. Conversely, the cathode is outlined because the place the place the discount takes place
and due to this fact it’s negatively charged in electrolysis processes. Word that the identical definition for electrodes
applies in a galvanic cell (e.g. in batteries), however because of the electron move the anode has a detrimental cost
whereas the cathode is positively charged (Determine 2.2).
Lithium could be remoted in an identical electrolytic course of utilizing lithium chloride (LiCl). Spodumene
(LiAlSi2O6) is the principle supply for LiCl, which is reacted to LiOH by heating with CaO and subsequent
conversion to LiCl previous to the electrolysis. Potassium can be obtained through electrolysis of KCl, however there
are extra environment friendly strategies, for instance, the response to a Na-Okay alloy which could be subsequently distilled.
2.1.2 Excursus: discount–oxidation reactions
The time period redox (quick for discount–oxidation) response describes all chemical reactions through which atoms
change their oxidation quantity. Redox reactions have many functions, which might vary from industrial
processes (see Downs’ course of) to organic programs, for instance, oxidation of glucose within the human physique.
A redox response incorporates the 2 ‘half-reactions’, particularly discount and oxidation, that are all the time one
set; which means there may be by no means a discount response with out an oxidation.
Redox reactions are a household of reactions that include oxidation and discount reactions. These are
all the time a matched set, that’s, there is no such thing as a oxidation response with no discount response. They’re referred to as
half-reactions, as two half-reactions are wanted to type a redox response. Oxidation describes the lack of
electrons (e−), whereas the time period discount is used for the achieve of electrons (e−).
22 Necessities of Inorganic Chemistry
• Discount: Describes the achieve of electrons or the lower within the oxidation state of an atom or molecule.
• Oxidation: Describes the lack of electrons or the rise within the oxidation state of an atom or molecule.
Discount ∶ Fe → Fe2+ + 2e−
Oxidation ∶ Cu2+ → Cu + 2e−
General redox response ∶ Fe + Cu2+ → Fe2+ + Cu (2.1)
Equation 2.1 offers an instance for a easy redox response.
The phrases oxidant and reductant are vital phrases used when discussing redox equations. An oxidant
is outlined because the atom or molecule that oxidises one other compound and in flip is lowered itself. Reductants
are molecules or atoms that scale back different compounds and because of this are oxidised themselves. Inside a redox
equation, there may be all the time the oxidant– reductant pair current.
Discount ∶ Oxidant + e− → Product
Lower in oxidation state (achieve of electrons)
Oxidation ∶ Reductant → Product + e−
Improve in oxidation state (lack of electrons) (2.2)
Equation 2.2 exhibits the involvement of an oxidant and a reductant in redox reactions.
220.127.116.11 The oxidation state
It’s really not exactly right to explain oxidation/discount reactions as loss/achieve of electrons. Each
reactions are higher referred to the adjustments in oxidation state reasonably than to the precise switch of electrons;
there are reactions categorized as redox response regardless that no switch of electrons takes place.
The oxidation state of an atom describes what number of electrons it has misplaced while interacting with one other
atom in comparison with its unique state (in its elemental type). The oxidation state is a hypothetical cost
that an atom would have if all bonds throughout the molecule are seen as 100% ionic. When a bond is fashioned,
it’s potential for an atom to achieve or lose electrons relying on its electronegativity. If an atom is electropositive, it’s extra prone to take electrons away from one other atom, and vice versa.
The oxidation quantity pertains to the variety of electrons that has been allotted to every atom; that
is, if an atom has gained an electron, its oxidation state is lowered by 1 and due to this fact this atom has the
oxidation state of – I.
IUPAC has outlined the oxidation state as follows: A measure of the diploma of oxidation of an atom in a
substance. It’s outlined because the cost an atom is perhaps imagined to have when electrons are counted in accordance
to an agreed-upon algorithm:
1. The oxidation state of a free factor (uncombined factor) is zero.
2. For a easy (monatomic) ion, the oxidation state is the same as the online cost on the ion.
3. Hydrogen has an oxidation state of 1 and oxygen has an oxidation state of −2 when they’re current in
most compounds (exceptions to this are that hydrogen has an oxidation state of −1 in hydrides of energetic
metals, e.g. LiH, and oxygen has an oxidation state of −1 in peroxides, e.g. H2O2).
Alkali Metals 23
+I +VII –II
+I +IV –II
Extraction of alkali metals: an introduction to redox chemistry