Characteristics and methods of obtaining chlorine, and its reaction with water

Chlo­rine was first de­scribed in the “Trea­tise on Py­ro­lusite” by the Swedish chemist Scheele. The sci­en­tist heat­ed the min­er­al py­ro­lusite with hy­drochlo­ric acid, and no­ticed a smell that was char­ac­ter­is­tic of aqua re­gia. He col­lect­ed the yel­low-green gas that caused this smell, and be­gan to study its in­ter­ac­tion with oth­er sub­stances. The chemist was the first to dis­cov­er the bleach­ing prop­er­ties of chlo­rine, and to no­tice the ef­fect of chlo­rine on gold and cinnabar. The el­e­ment was named by the sci­en­tist Davy, who stud­ied the poi­sonous gas ex­ten­sive­ly.

Gen­er­al char­ac­ter­is­tics of chlo­rine

Chlo­rine is a halo­gen, a very pow­er­ful ox­i­diz­er, an ex­treme­ly poi­sonous gas and an im­por­tant prod­uct of the chem­i­cal in­dus­try. It is a raw ma­te­ri­al for the man­u­fac­ture of tox­ic chem­i­cals, plas­tics, ar­ti­fi­cial fiber, rub­ber, medicines and dyes. It is used to ob­tain sil­i­con, ti­ta­ni­um, flu­o­ro­plas­tic and glyc­erin. Chlo­rine is used to bleach fab­rics and pu­ri­fy drink­ing wa­ter.

In or­di­nary con­di­tions, chlo­rine is a heavy yel­low-green gas with a char­ac­ter­is­tic smell. Its atom­ic weight is – 35.453, and its molec­u­lar weight is 70.906. One liter of chlo­rine in gaseous state in nor­mal con­di­tions weighs 3.214 g. If chlo­rine is cooled to a tem­per­a­ture of -34.05 de­grees Cel­sius, the gas con­den­sates into a yel­low liq­uid, and at a tem­per­a­ture of -101.6 de­grees Cel­sius, it be­comes sol­id.

At high pres­sure, chlo­rine turns into a liq­uid even at high­er tem­per­a­tures. This gas has a high ac­tiv­i­ty – it com­bines with al­most ev­ery el­e­ment in the pe­ri­od­ic ta­ble. For this rea­son, in na­ture chlo­rine is en­coun­tered ex­clu­sive­ly in the form of com­pounds. Chlo­rine is found in such min­er­als as halite, sylvi­nite, bishof­ite, car­nal­lite and kai­nite. These min­er­als are “to blame” for the fact that the earth’s crust has a 0.17% chlo­rine con­tent by weight. For non-fer­rous met­al­lur­gy, such rel­a­tive­ly rare min­er­als con­tain­ing chlo­rine as horn sil­ver are im­por­tant. Liq­uid chlo­rine is among the strong­est iso­la­tors of elec­tri­cal con­duc­tiv­i­ty – the sub­stance con­ducts a cur­rent al­most one mil­lion times worse than dis­tilled wa­ter, and a thou­sand times worse than sil­ver. The speed of sound in chlo­rine is 1.5 times less than in wa­ter.

At present, nine iso­topes of chlo­rine are known to sci­ence, but in na­ture just 2 are en­coun­tered – chlo­rine-35 and chlo­rine-37. Chlo­rine-35 is three times more com­mon than chlo­rine-37. Sev­en of the nine iso­topes are ob­tained ar­ti­fi­cial­ly. The short­est-lived iso­tope, chlo­rine-32, has a half-life of 0.306 sec­ond, and the long­est-lived is chlo­rine-36, which can “live” for 310,000 years.

Meth­ods of ob­tain­ing chlo­rine

The man­u­fac­ture of chlo­rine re­quires a great deal of elec­tric­i­ty to break down the nat­u­ral com­pounds of the el­e­ment. The main raw ma­te­ri­al for chlo­rine is or­di­nary rock salt, an in­ex­pen­sive prod­uct that is used in large quan­ti­ties (to ob­tain 1 ton of chlo­rine, at least 1.7 tons of salt is re­quired). You can do an in­ter­est­ing and very easy ex­per­i­ment on ob­tain­ing chlo­rine through na­tri­um chlo­ride elec­trol­y­sis even at home.

First the salt is crushed, then dis­solved in warm wa­ter. The ob­tain so­lu­tion is pumped into a pu­ri­fy­ing room, where potas­si­um and mag­ne­sium salts are re­moved, and then it is clar­i­fied (al­lowed to set­tle). The pure con­cen­trat­ed so­lu­tion of sodi­um chlo­ride is pumped into a cell room.

There are two types of in­dus­tri­al pro­duc­tion of chlo­rine: the mer­cury and di­aphragm meth­ods. In the sec­ond case, a per­fo­rat­ed sheet of iron acts as the cath­ode, and the cath­ode and an­ode sec­tions of the elec­trolyt­ic cells are sep­a­rat­ed by an as­bestos di­aphragm. Hy­dro­gen ions are dis­charged on the iron cath­ode, and a wa­ter so­lu­tion of caus­tic sodi­um forms. When mer­cury is used as the cath­ode, sodi­um ions are dis­charged and a sodi­um amal­gam forms, which is then bro­ken down by wa­ter. Hy­dro­gen and caus­tic sodi­um form. In this case the sep­a­rat­ing di­aphragm is not need­ed, and the al­ka­line has a high con­cen­tra­tion.

The man­u­fac­ture of chlo­rine si­mul­ta­ne­ous­ly in­volves the man­u­fac­ture of hy­dro­gen and caus­tic sodi­um. The hy­dro­gen is re­moved in met­al pipes, and the chlo­rine in ce­ram­ic or glass pipes. “Fresh” chlo­rine is sat­u­rat­ed with wa­ter va­por, and for this rea­son dis­plays its most ag­gres­sive prop­er­ties. Chlo­rine is first cooled with cold wa­ter in tow­ers lined with ce­ram­ic tiles, then dried with con­cen­trat­ed sul­fu­ric acid, which is the only dry­ing agent of chlo­rine which the el­e­ment does not re­act with.

Dry chlo­rine is less ag­gres­sive and does not have a de­struc­tive ef­fect on met­al. Chlo­rine is trans­port­ed in liq­uid state in cylin­ders un­der a pres­sure of up to 10 at­mos­pheres, or in rail­way tanks. To com­press and pump chlo­rine at fac­to­ries, pumps with sul­fu­ric acid are used, which also per­form the role of a lu­bri­cant and work­ing medi­um at the same time.

The re­ac­tion of chlo­rine with wa­ter

Chlo­rine dis­solves in wa­ter, and at 20 de­grees Cel­sius 2.3 vol­umes of chlo­rine dis­solve in one vol­ume of wa­ter. Ini­tial­ly, the wa­ter so­lu­tion of chlo­rine is yel­low, but if it is stored in light for a long time, the so­lu­tion grad­u­al­ly los­es its col­or. This is be­cause the dis­solved chlo­rine en­ters into a par­tial re­ac­tion with wa­ter, form­ing hy­drochlo­ric and hypochlor­ous acids. The chlo­rine so­lu­tion in wa­ter grad­u­al­ly turns into a so­lu­tion of hy­drochlo­ric acid, as hypochlor­ous acid is un­sta­ble and grad­u­al­ly breaks down into hy­dro­gen chlo­ride and oxy­gen.

At low tem­per­a­tures, chlo­rine and wa­ter en­ter into a re­ac­tion and form a crys­tal­lo­hy­drate of an un­usu­al com­po­si­tion. These are crys­tals of a green-yel­low col­or, which are only sta­ble at a tem­per­a­ture be­low 10 de­grees Cel­sius, and are formed when chlo­rine is passed through wa­ter con­tain­ing ice. In the crys­tal struc­ture of ice, wa­ter mol­e­cules can be ar­ranged so that even­ly po­si­tioned spa­ces ap­pear be­tween them. An el­e­men­tary cu­bic cell con­tains 46 wa­ter mol­e­cules, with 8 mi­cro­scop­ic spa­ces be­tween them. The chlo­rine mol­e­cules set­tle in these spa­ces.