CHLORINE AND ITS COMPOUNDS

CHLORINE AND ITS COMPOUNDS
This is the most important element of all the Halogens. It is in period 7 because it has 7 valence electrons and in period three because it has three shells. It is a greenish yellow gas and it is found in abundance in NaCl ( common salt). Other elements are Flourine, Bromine, Iodine and Astatine. They all require one electron to be fully filled and complete their octect hence their great reactivity.
LABORATORY PREPARATION
It is prepared by the oxidation of concentrated hydrochloric acid with a strong oxidizing agent such as Mangenese (iv) oxide, potassium tetraoxomanganate (vii) or lead (iv) oxide.

1. USING MnO2
   Heat a mixture of MnO2 and conc. HCl. The acid is oxidized to liberate chlorine.
   (WRITE EQUATION HERE)
2. USING KMnO4
   It oxidizes conc. HCl to liberate chlorine.
   (WRITE EQUATION HERE)
   INDUSTRIAL PREPARATION
   Chorine is manufactured industrially by the electrolysis of
3. brine
4. the chlorides of molten sodium, magnesium or calcium.
   Chlorine gas is collected by downward delivery ( i.e. upward displacement of air) because it is denser than air.
   PHYSICAL PROPERTIES
5. It is a greenish-yelloq gas with an unpleasant chocking smell.
6. It is moderately soluble in water.
7. It is about 2.5 times denser than air.
8. It can easily be liquified.
9. It is poisonous.
   CHEMICAL PROPERTIES
   Because it has 7 valence electrons, it is very reactive and tries to achieve a stable octet either
10. By gaining an electron from Groups 1 and 2 to form NaCl or CaCl2 or by sharing a pair of electrons in a single covalent bond with another atom as in gaseous chlorine ( Cl-Cl) or hydrogen chloride ( H-Cl)
11. DISPLACEMENT OF OTHER HALOGENS
    With the exception of flourine, chlorine can displace any of the other halogens from solutions of their respective acuds and salts. This is because it is more reactive than the halogen it replaces. E.g
    (A) Cl2(g) + 2NaBr(aq) to give 2NaCl(aq) + Br2(l)
    (B) Cl2(g) + 2 HI (aq) to give 2HCl(aq) + I2(s)
    The above reactions are displacement reactions.
12. DIRECT COMBINATION WITH OTHER ELEMENTS
    (A) With metals: It reacts with metals to form a corresponding chlorides.
    (i) 2Na(s) + Cl2(g) to give 2 NaCl (s)
    (ii) 2 Fe(s) + 3 Cl2(g) to give 2 FeCl3(s)
    In the second equation, FeCl3 is formed and NOT FeCl2 due to the oxidizing nature of chlorine.
    B. With Non-metals: With the exception of the noble gases, oxygen, nitrogen and carbon, all other non- metals burn in chlorine to produce the corresponding chlorides. Hydrogen and chlorine combine explosively in bright sunlight, although the reaction is slower in diffused light.
    C. Reactions with Hydrogen
    (i) with hydrocarbons: a piece of filter paper saturated with warm turpentine (C10H18) will rapidly catch fire in a jar of chlorine, forming soot ( a black deposit of carbon)
    C10H16(l) + 8 Cl2(g) to give 10 C(s) + 16 HCl(g).
    Under controlled conditions, substitution reaction occur. Chlorine reacts with saturated hydrocarbons to produce chlorinated hydrocarbons and hydrogen chloride.
    CH4(g) + Cl2(g) to give CH3Cl(g) + HCl(g)
    (ii) with ammonia :
    Chlorine will remove hydrogen from ammonia with the formation of nitrogen and hydrogen chloride. The later then combines with excess ammonia to form ammonium chloride.
    2NH3(g) + 3 Cl2(g) to give N2(g) + 6HCl (g)
    HCl (g) + NH3(g) to give NH4Cl.
    (iii) with Hydrogen sulphide:
    When chlorine and hydrogen sulphide are mixed, a yellow deposit of sulphur is formed as a result of the oxidation of the sulphide by the chlorine.
    H2S(g) + Cl2(g) to give 2HCl(g) + S (s)
    (iv) with water
    Chlorine water ( HoCl) is formed by bubbling chlorine through water. Oxygen gas is given off when exposed to sunlight.
    . AS AN OXIDIZING AGENT
    Chlorine is a powerful oxidizing agent because of its ability to remove hydrogen and its readiness to accept electrons from reducing agents to form chloride ions. Examples are:
    (i) with iron(ii) salts : It oxidizes a solution of green iron (ii) chloride to yellow iron (iii) chloride
    2 FeCl2(aq) + Cl2(g) to give 2 FeCl3(aq)
13. AS A BLEACHING AGENT
    In the presence of water, chlorine bleaches most dyes and inks, except those containing carbon e.g printer’s ink. The bleaching action of chlorine is due to its ability to react with water to form oxochlorate (i) acid. The latter is unstable and decomposes to release oxygen which oxidizes the dye to form colourless compound.
    HOCl(aq) to give HCl(aq) + [O]
14. REACTION WITH ALKALIS
    (a) with dilute alkali solution:
    When chlorine is bubbled through cold dilute solution of sodium hydroxide, a pale-yellowish mixture of the oxochlorate (i) acid and chloride of the metal is formed.
    Cl2(g) + 2NaOH(aq) to give NaOCl(aq) + NaCl(aq) + H2O(l)
    (b) with concentrated alkali solutions:
    If chlorine is bubbled through a hot concentrated solution of sodium hydroxide, a mixture of the trioxochlorate (v) and chloride of the metal is formed.
    3Cl2(g) + 6 NaOH(aq) to give NaClO3(aq) + 5 NaCl (aq) + 3 H2O(l)
    TEST FOR CHLORINE
    (a) With damp litmus paper test: Drop a piece of damp blue litmus paper into a gas jar of the unknown gas. If the litmus paper turns pink and then becomes bleached, the gas is chlorine.
    (b) Starch-iodide paper test : Drop a piece of damp starch-iodide paper into the unknown gas. If the paper turns dark blue, then the gas is chlorine. Chlorine turns Starch-iodide paper blue because it displaces iodine from the iodide. The iodine liberated then turns the starch blue.
    2KI(aq) + Cl2(g) to give 2KCl(aq) + I2(s)

USES

1. It is used as a powerful germicide because of its oxidizing nature. It is used in the sterilisation of water for domestic and industrial use and in the treatment of sewage.
2. It is used as a bleaching agent for cotton, linen and wood pulp.
3. Chlorine is used in the manufacture of:
   (a) important organic solvents like CHCl3 and CCl4
   (b) poly vinyl chloride and synthetic rubber
   (c) hydrochloric acid
   (d) in making matches and fireworks
   (e) bleaching agents such as bleaching powder
   (f) domestic antiseptic