# 18.2 Occurrence and preparation of the representative metals  (Page 2/7)

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## The preparation of aluminum

The preparation of aluminum utilizes a process invented in 1886 by Charles M. Hall , who began to work on the problem while a student at Oberlin College in Ohio. Paul L. T. Héroult discovered the process independently a month or two later in France. In honor to the two inventors, this electrolysis cell is known as the Hall–Héroult cell    . The Hall–Héroult cell is an electrolysis cell for the production of aluminum. [link] illustrates the Hall–Héroult cell.

The production of aluminum begins with the purification of bauxite, the most common source of aluminum. The reaction of bauxite, AlO(OH), with hot sodium hydroxide forms soluble sodium aluminate, while clay and other impurities remain undissolved:

$\text{AlO}\left(\text{OH}\right)\left(s\right)+\text{NaOH}\left(aq\right)+{\text{H}}_{2}\text{O}\left(l\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}\text{Na}\left[\text{Al}{\left(\text{OH}\right)}_{4}\right]\left(aq\right)$

After the removal of the impurities by filtration, the addition of acid to the aluminate leads to the reprecipitation of aluminum hydroxide:

$\text{Na}\left[\text{Al}{\left(\text{OH}\right)}_{4}\right]\left(aq\right)+{\text{H}}_{3}{\text{O}}^{\text{+}}\left(aq\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}\text{Al}{\left(\text{OH}\right)}_{3}\left(s\right)+{\text{Na}}^{\text{+}}\left(aq\right)+{\text{2H}}_{2}\text{O}\left(l\right)$

The next step is to remove the precipitated aluminum hydroxide by filtration. Heating the hydroxide produces aluminum oxide, Al 2 O 3 , which dissolves in a molten mixture of cryolite, Na 3 AlF 6 , and calcium fluoride, CaF 2 . Electrolysis of this solution takes place in a cell like that shown in [link] . Reduction of aluminum ions to the metal occurs at the cathode, while oxygen, carbon monoxide, and carbon dioxide form at the anode.

## The preparation of magnesium

Magnesium is the other metal that is isolated in large quantities by electrolysis. Seawater, which contains approximately 0.5% magnesium chloride, serves as the major source of magnesium. Addition of calcium hydroxide to seawater precipitates magnesium hydroxide. The addition of hydrochloric acid to magnesium hydroxide, followed by evaporation of the resultant aqueous solution, leaves pure magnesium chloride. The electrolysis of molten magnesium chloride forms liquid magnesium and chlorine gas:

${\text{MgCl}}_{2}\left(aq\right)+\text{Ca}{\left(\text{OH}\right)}_{2}\left(aq\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}\text{Mg}{\left(\text{OH}\right)}_{2}\left(s\right)+{\text{CaCl}}_{2}\left(aq\right)$
$\text{Mg}{\left(\text{OH}\right)}_{2}\left(s\right)+\text{2HCl}\left(aq\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}{\text{MgCl}}_{2}\left(aq\right)+{\text{2H}}_{2}\text{O}\left(l\right)$
${\text{MgCl}}_{2}\left(l\right)\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}\text{Mg}\left(l\right)+{\text{Cl}}_{2}\left(g\right)$

Some production facilities have moved away from electrolysis completely. In the next section, we will see how the Pidgeon process leads to the chemical reduction of magnesium.

## Chemical reduction

It is possible to isolate many of the representative metals by chemical reduction    using other elements as reducing agents. In general, chemical reduction is much less expensive than electrolysis, and for this reason, chemical reduction is the method of choice for the isolation of these elements. For example, it is possible to produce potassium, rubidium, and cesium by chemical reduction, as it is possible to reduce the molten chlorides of these metals with sodium metal. This may be surprising given that these metals are more reactive than sodium; however, the metals formed are more volatile than sodium and can be distilled for collection. The removal of the metal vapor leads to a shift in the equilibrium to produce more metal (see how reactions can be driven in the discussions of Le Châtelier’s principle in the chapter on fundamental equilibrium concepts).

#### Questions & Answers

what is caustic soda
sodium hydroxide (NaOH)
Kamaluddeen
what is distilled water
Rihanat
is simply means a condensed water vapour
Kamaluddeen
advantage and disadvantage of water to human and industry
a hydrocarbon contains 7.7 percent by mass of hydrogen and 92.3 percent by mass of carbon
how many types of covalent r there
how many covalent bond r there
JArim
they are three 3
what is an atom
why is an atom
Rabiu
u answer me first
Atom is indivisible particles which take place in chemical reactions
Samuel
OK
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what is half reaction?
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Zn(OH-)2
Pookieman
what is atomicity
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what is coordination number
coordination number is the number of atoms or ions immediately surrounding a central atom in a complex or crystal
Chidera
what is isotope
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who is the father of chemistry
Antoine Lavoisier. Father of modern chemistry
Yapi
Lavoisier
Simbiat
What is geometric isomerism
jo
Lakshmi
pls I don't really know teach me
Joel
geometric isomerism are molecules that are locked into their spatial position with respect to one another due to a double Bond or ring structure
Chidera
Chromatography is a physical method of seperation where by mixtures that are in two phrases are separated
What is chromatography?