AOAC Official Method 935.09 Chlorine (Available) in Calcium Hypochlorite and Bleaching Powder Arsenious Oxide Titration Method
First Action 1935
Final Action
Weigh 5–10 g thoroughly mixed test sample into porcelain mortar,add 30–40 mL H2O, and triturate to smooth cream [high-test Ca(OCl)2 will dissolve readily and not form a cream]. Add more H2O, stir well with pestle, and let insoluble residue settle few moments. Pour mixture off into 1 L volumetric flask, add more H2O, and thoroughly triturate sample and pour off as before. Repeat operation until all material is transferred to flask. Rinse mortar and pestle, catch wash H2O in flask, dilute to volume, and mix. Without letting material settle, pipet 25–50mLaliquot into 200mLErlenmeyer.Addexcess standardAs2O3 solution, 935.07A(a) (see 7.2.33), and then decided excess ofNaHCO3.
Titrate excess As2O3 with standard I2 solution, 935.07A(b) (see 7.2.33), using starch solution, 922.03A(f) (see 7.1.05), or I2 as its own indicator.
Subtract volume I2 solution, corrected to 0.1M, from volume As2O3 solution used, and calculate percent available Cl. 1 mL 0.025M As2O3 =
0.003545 g available Cl.
Reference: JAOAC 18, 65(1935).
CAS-7778-54-3 (calcium hypochlorite)
