- Percent active chlorine
Percent active chlorine is a unit of
concentration used for hypochlorite-basedbleach es. One gram of a 100% active chlorine bleach has the same bleaching power as one gram ofchlorine . The term "active chlorine" is used because most commercial bleaches contain substantial amounts of chlorine in the form ofchloride ions, which have no bleaching properties.Liquid bleaches sold for domestic use are typically 3–10% active chlorine, and should be diluted to 1–2% active chlorine before use. Commercial domestic bleaching powder is typically about 40% active chlorine. Values for some industrial solid bleaches are given in the table below.
Values can be higher than 100% because
hypochlorite ion have higher oxidation state (+1) thanchlorine (0) and so high oxidation power .
Percent active chlorine values have now virtually replaced the older system ofchlorometric degree s: 1% active chlorine is equivalent to 3.16 °Chl. Taking the (reasonable) assumption that all active chlorine present in a liquid bleach is in the form of hypochlorite ions, 1% active chlorine is equivalent to 0.141 mol/Kg ClO−(0.141 mol/L if we assume density=1). For a solid bleach, 100% active chlorine is equivalent to 14.1 mol/kg ClO−:lithium hypochlorite has amolar mass of 58.39 g/mol, equivalent to 17.1 mol/kg or 121% active chlorine.Active chlorine values are usually determined by adding an excess of
potassium iodide to a sample of bleach solution and titrating theiodine liberated with standardsodium thiosulfate solution.::Cl2 + 2I− → I2 + 2Cl−or::ClO− + 2I− + 2 H+ → I2 + H2O + Cl−then::2S2O32− + I2 → S4O62− + 2I−From the above equations it can be seen that 2 mole of thiosulfate is equivalent to 70.9 grams of active chlorine.
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