Chlorine bleaching power

Some papermakers allow the half-stuff and chlorine to remain from forty-fivo to fifty minutes in the blcach-ing-engine, under the impression that the color is thereby improved. It cannot be denied that tire color improves very rapidly nnder tho process but when it is continued more than twenty minutes, the action of the roll on the stuff causes the chlorine to evaporate, which is easily perceived by the smell, and greatly reduces the bleaching powers of the liquor. 

Chlorine dioxide has 2lh times the bleaching power of chlorine and is important in water purification, for odor control, and for pulp bleaching. 

Read the discussion of the hydrolysis of bromine in the preceding preparation. About one-third of the chlorine in chlorine water is hydrolyzed. The bleaching power of chlorine is due directly to the oxidizing action of the hypochlorous acid produced by the hydrolysis. The formation of chlorate in this preparation is also a result of the oxidizing action of hypochlorous add. 

From these equations it is evident that 1 mole of chlorine has the same oxidation power as one gram-ion of CIO- (i. e. one mole of NaCIO or half a mole of Ca(C10)2), half a inole of NaC102. or finally, two fifths of a mole of chlorine dioxide. For example, one gram-molecule of pure calcium hypochlorite of 142.99 grams in weight has the same bleaching power as two moles of chlorine weighing 141.84 g. The content of active chlorine in this substance thus equals 141.84/142.99 = 99.19 per cent. 

Berthollet, C. L. (1748-1822). Corrected Lavoiser s theory of acids discovered bleaching power of chlorine studied combining weights of atoms (stoichiometry). 

Water absorbs about 100 times its volume of this gas, and acquires a pale yellow colour, and the astringent, not acid, taste and peculiar smell of the gas. It bleaches powerfully, and is easily decomposed by all substances which have a strong affinity for chlorine, or for oxygen. 

Chlorine is used as a bleach and disinfectant, but totally dry chlorine has no bleaching power. Chlorine owes its bleaching capability to the hypochlorous acid, HCIO, that is formed when chlorine reacts with water. Once the HCIO is formed, it readily gives up oxygen, O, to any nearby oxidizable substance. The following chemical equations describe these two reactions ... 

Aqueous sodium hypochlorite, NaOCl(aq), is a powerful oxidizing agent. It is the active ingredient in many liquid chlorine bleaches. The bleaching action of NaOCl(aq) is associafed wifh the reduction of the OCP ion to CP the electrons required for the reduction come from colored compounds in stains. The bleaching action of NaOCl(aq) is demonsfrated in Figure 5-17. 

Liquid chlorine dioxide, ClOj, boils at 284 K to give an orange-yellow gas. A very reactive compound, it decomposes readily and violently into its constituents. It is a powerful oxidising agent which has recently found favour as a commercial oxidising agent and as a bleach for wood pulp and flour. In addition, it is used in water sterilisation where, unlike chlorine, it does not produce an unpleasant taste. It is produced when potassium chlorate(V) is treated with concentrated sulphuric acid, the reaction being essentially a disproportionation of chloric(V) acid ... 

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