Sodium hypochlorite Starch iodide paper

NaOH this fact is especially important in the preparation of hypochlorite solutions. The temperature should not be allowed to rise above 60° or yellow dyes of the Mikado series are formed. The mixture is allowed to stand at least 4 hours at 55°, during which time it should give a positive test for active chlorine with starch-iodide paper. The solution is then cooled to 15° and allowed to stand for a day after 400 grams of salt has been added. Sodium dinitrostilbenedisulfonate separates as a yellow, crystalline precipitate, and this is filtered off and washed with a small volume of salt solution. 

Add a drop of the reaction mixture to a piece of starch-iodide paper. Any unreacted hypochlorite will cause the appearance of the blue starch-triiodide complex. Add 1-mL portions of saturated sodium bisulfite solution to the reaction mixture until the starch-iodide test is negative. 

A solution of 4 mmoles of (1) in 25 ml. of water was covered with 10 ml. of benzene, and 14 ml. of commercial 5% sodium hypochlorite was added dropwise in 20 min. A spot test on starch-iodide paper taken after each addition was negative after 30 seconds until the end point had been reached. The layers were separated and the basic aqueous layer was extracted with ether-benzene. 

Place the mixture in an ice bath on a magnetic stirrer. While the mixture is stirring, slowly add 3 mL of a 6% aqueous sodium hypochlorite solution to the mixture. Be careful not to allow the reaction temperature to rise above 30°C by controlling the rate of addition. Allow the solution to stir for 1 hour. In order to determine whether or not there is excess hypochlorite, test the solution periodically by placing a drop of the reaction mixture on a strip of potassium iodide starch test paper. A blue-black color indicates that there is an excess of hypochlorite. If there is no color change, add an additional 0.5 mL of sodium hypochlorite solution, stir for several minutes, and repeat the starch-iodide test. Continue this process until the paper turns blue-black. 

Because the concentration of sodium hypochlorite in bleach depends on the age of the solution, it is important to monitor the oxidation of 1 with starch/iodide test paper to ensure that excess oxidant is present. The test paper should turn blue-black owing to the formation of the complex of starch and iodine that is produced upon oxidation of iodide ion by the hypochlorite ion. On the other hand, commercially available calcium hypochlorite is quite stable and maybe stored at room temperature without decomposition. Therefore, the amoimt of oxidant used is easy to determine, but it is still good practice to ensure that an excess of oxidant is present by applying the starch/iodide test, especially if the reaction mixture is heated. Excess oxidant may be reduced at the end of the experiment using sodium bisulfite, NaHSOj. 

Method of Pan and Dutcher). Spray paper with sodium hypochlorite (dil. 1 part 5.25% sodium hydrochlorite to 20 parts water). Dry. Spray with 95% ethanol. Dry. Spray with starch-iodide reagent (1% aq. soluble starch-1 % aq. potassium iodide, I I). Acelylated spots show up as deep blue zones against a colorless background... 

---