B. Physical Properties of Cl2

 

Molecular mass:	70.906 g/mol
melting point:	-100.98 oC
boiling point:	-34.6 oC

Scheele noted the bleaching power of the gas and within eleven years numerous patents appeared covering this process.  Another scientist interested in chlorine was the French physician Claude Louis Berthollet.  Several bleaching processes patented by Berthollet in 1785 are still used today.

     Sir Humphry Davy correctly identified Scheele's gas as an element in 1810 and he proposed the name 'chlorine' which comes from the Greek word khloros which means 'yellow-green.'  Chlorine was used throughout Europe in the early 19th century as a disinfectant and germicide in order to control a cholera epidemic.

     Chlorine was used as a trench warfare gas in 1915.
 
 

D. Natural Abundance
     Chlorine does not occur in elemental form in nature.  The vast majority is in the form of NaCl salt deposits which were produced from ancient seas.  Sodium chloride is also the major salt present in the earth's oceans.  In terms of natural occurrence in the earth's crust (which includes the oceans), chlorine ranks 20th at 0.065%.  Chlorine is found in the minerals halite (NaCl), carnallite (KMgCl3^.6 H2O), and sylvite (KCl).  Like most of the minerals present in ocean and sea water, the sodium chloride present was carried there by rivers and run-off over the course of billions of years.
 

E. Industrial Production
 

Chlorine has extensive uses in society and is one of the world's most important chemicals being manufactured on a large scale.  Chlorine ranks 8th in terms of the quantities of chemicals manufactured in the USA.  Industrial production of chlorine up through the 1970's and 80's involved the electrolysis of brine solutions, NaCl(aq) using an asbestos diaphragm cell and a mercury cathode electrode.  For environmental reasons, this design has been all but replaced in modern countries by the Nafion ion-permeable membrane cell shown in Figure 1.      The Nafion membrane is made of fluorine-containing polymers including Teflon.  Its salient feature is to allow Na+(aq) ions to pass from one chamber to the other.  In the left chamber brine solution enters the anode chamber where the chloride is oxidized to chlorine:

Figure 1

Pure water enters the cathode chamber where it is reduced to H2(aq) and OH^-(aq):

Sodium hydroxide, NaOH(aq), another commercially important product, leaves the cathode chamber.  The overall reaction is:

F. Industrial Uses
     Chlorine is used in virtually every country as a disinfectant of water supplies.  Much of the chlorine produced is used in the manufacture of household bleach, NaOCl(aq).  Industrial strength bleaches are used in pulp bleaching.  Chlorine compounds are used to make dyes, textiles, medicines, insecticides, solvents, paints, and plastics.  The plastic polyvinylchloride, 'PVC' is made from the monomer vinyl chloride which ranks 15th in terms of quantities of chemicals manufactured in the USA.

G. Gas Density of Cl2
     The density of Cl2 is 2.898 g/L at 25 ^oC and 1 atm.  It has a density that is 2.45 times greater than that of air.

H. Gas Solubility of Cl2
     Chlorine is fairly soluble in water and colors it yellow-green.  Under standard conditions, 3.1 volumes of Cl2 will dissolve per 1 volume of water.  At 10 ^oC, 14.6 g Cl2 dissolve per L H2O; this corresponds to 4.62 volumes Cl2 per 1 volume water.