Metals and their compounds
Sodium and its compounds
Extraction of sodium
Sodium does not occur free in nature because it is
too reactive. It is found in sea water as sodium
chloride, sodium bromide and sodium iodide. It
also occurs in deposits as sodium chloride (rock
salt).
Sodium metal is extracted industrially by
electrolysis of its fused (molten ) chloride using
the Downs cell
As the melting point of sodium chloride is high
(800oC), calcium chloride is added to lower the
melting point to 600oC. Downs’ cell is made up of
graphite rod which serves as the anode while the
cathode is a steel cylinder. This is because
chlorine gas liberated at the anode will not attack
graphite , but will attack steel. Sodium metal is
deposited at the cathode.
Electrolyte ionizes: NaCl (s)  Na+(l) + Cl- (l)
At the anode (+): ClThe chloride ions give up an electron each, and
become oxidized to atomic chlorine, which then
pair up to form gaseous chlorine molecules.
Cl-  Cl + eCl + Cl  Cl2
At the cathode: the sodium ions receive an
electron each, and become reduced to metallic
sodium.
Na+ + e-  Na
Properties of sodium
Physical Properties
• Sodium is a soft, silvery metal; it can be cut with
a knife
• It is a good conductor of heat and electricity
• It has relatively low melting and boiling points
Chemical Properties
1)Exposure to moist air: sodium tarnishes easily
when exposed to air because it is readily oxidized
by atmospheric oxygen. This reacts with water to
form sodium hydroxide, which then reacts with
carbon (IV) oxide to form an aqueous solution of
sodium trioxocarbonate (IV).
Na(s) + O2(g)  Na2O (s)
Na2O(s) + H2O(g)  NaOH(aq)
NaOH(aq) + CO2(g)  Na2CO3(s) + H2O(l)
2) Reaction with dilute acid: sodium displaces hydrogen from dilute
acid in a violent manner as the metal is higher than hydrogen in the
activity series.
Na + HCl  NaCl + H2
3) Reaction with cold water: when a small piece of sodium metal is
dropped in a large dish of cold water, it darts about the surface with
hissing sound, liberating much heat, together with an odourless and
colourless hydrogen gas. The resulting solution of sodium hydroxide is
alkaline, it turns red litmus paper to blue and turns phenolphthalein
indicator pink , or methyl orange to yellow
Na(s) + H2O(l)  2NaOH + H2(g)
4) Reaction with non-metals: sodium reacts readily with non-metals, such
as hydrogen, chlorine and sulphur, to give the corresponding ionic
compounds
Na(s) + H2(g)  2NaH(s)
5) Flame Test: sodium and its compounds impart golden-yellow
colourations to the Bunsen burner flame.