Bleaches solution/suspension

Bleaching powder is important in textile industry and in paper and pulp bleaching. In textile industry, the fabric to be bleached is first treated with caustic soda solution to remove grease. It is then dipped in a suspension of bleaching powder and left exposed to air. The fabric is then treated with dilute hydrochloric acid to remove any excess of bleaching solution. Lastly it is treated with an antichlor such as sodium thiosulphate to remove excess chlorine and finally washed with water. 

Procedure (iodometric method). Weigh out accurately about 5.0 g of the bleaching powder into a clean glass mortar. Add a little water, and rub the mixture to a smooth paste. Add a little more water, triturate with the pestle, allow the mixture to settle, and pour off the milky liquid into a 500 mL graduated flask. Grind the residue with a little more water, and repeat the operation until the whole of the sample has been transferred to the flask either in solution or in a state of very fine suspension, and the mortar washed quite clean. The flask is then filled to the mark with distilled water, well shaken, and 50.0 mL of the turbid liquid immediately withdrawn with a pipette. This is transferred to a 250 mL conical flask, 25 mL of water added, followed by 2 g of iodate-free potassium iodide (or 20 mL of a 10 per cent solution) and 10 mL of glacial acetic acid. Titrate the liberated iodine with standard 0.1M sodium thiosulphate. 

Caution This procedure should be conducted in a good hood. The slurry is stirred while being heated on a steam bath, and solid sodium hydrosulfite is added until the red color of the nitroso compound is completely bleached (Note 5). Then an additional 30 g. of sodium hydrosulfite is added the light tan suspension is stirred with heating for 15 minutes more and is then allowed to cool. The dense diaminouracil bisulfite is filtered from the cooled solution, washed well with water, and partially dried. 

The high photostability and acute fluorescence intensity are two major features of DDSNs compared to dye molecules in a bulk solution. The early DDSN studies have focused on these two properties [8, 13]. For example, Santra et al. studied the photostability of the Ru(bpy)32+ doped silica nanoparticles. In aqueous suspensions, the Ru(bpy)32+ doped silica nanoparticles exhibited a very good photostability. Irradiated by a 150 W Xenon lamp for an hour, there was no noticeable decrease in the fluorescence intensity of suspended Ru(bpy)32+ doped silica nanoparticles, while obvious photobleaching was observed for the pure Ru(bpy)32+ and R6G molecules. To eliminate the effect from Brownian motion, the authors doped both pure Ru(bpy)32+ and Ru(bpy)32+-doped silica nanoparticles into poly(methyl methacrylate). Under such conditions, both the pure Ru(bpy)32+ and Ru(bpy)32+ doped silica nanoparticles were bleached. However, the photobleaching of pure Ru(bpy)32+ was more severe than that of the Ru(bpy)32+ doped silica nanoparticles. 

Hypochlorite. Sodium hypochlorite, [CAS 7681-52-9], NaOCl, commonly in solution by (1) electrolysis of sodium chloride solution under proper conditions. (2) reaction of calcium hypochlorite suspension in water and sodium carbonate solution, and then filtering. Used (1) as a bleaching agent fa textiles and paper pulp. (2) as a disinfectant, especially fa water. (3) as an oxidizing reagent. 

Action of Aqueous Alkaline Oxidizing Agents. Prepare a sodium hypochlorite solution by stirring bleaching powder and an excess Na2C03 solution and filtering. Place about 2 cc. of thin suspensions of each of the hydroxides prepared in Experiment 4 in separate test tubes and treat each with excess NaOH and the sodium hypochlorite solution. 

J) Color Reactions of Arylamines. To 10 ml of water in a test tube add one drop of aniline, and shake. Add one or two drops of a suspension of bleaching powder or a drop of a solution of sodium hypochlorite. Note the color. Repeat with o-toluidine, and with dimethylaniline. The production of color is due first to oxidation, and second, to condensation to complex colored compounds. 

Hypochlorite, H stage, bleaching employs a solution of either calcium or sodium hypochlorite in water, made at the pulp mill by adding chlorine to a suspension of lime or sodium hydroxide in water (Eqs. 15.44 and 15.45). 

Available chlorine in a sample of bleaching powder is estimated volumetrically. A known mass of bleaching powder as a suspension in water is treated with excess of potassium iodide solution. The solution is then acidified with a strong solution of acetic acid. Iodine is liberated which is titrated against standard sodium thiosulphate solution. 

The dye Rose-Bengal, in solution or as a suspension, is a very suitable sensitizer for generating singlet oxygen (Foote, 1%8 Kearns, 1971). There are several limitations to the dyes as photosensitizers (a) When the sensitizer is used in a solution, solvents which can be used for the reaction are limited, (b) The dye bleaches if longer reaction times are used, (c) The dye can sometimes react with the reactants or with the products, (d) Separation of the products from the dye in the reaction mixture is often difficult. 

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