Percent active chlorine 2524286 178645628 2007-12-18T03:24:17Z Alchie1 380436 '''Percent active chlorine''' is a unit of [[concentration]] used for [[Hypochlorous acid|hypochlorite]]-based [[bleach]]es. One gram of a 100% active chlorine bleach has the same bleaching power as one gram of [[chlorine]]. The term "active chlorine" is used because most commercial bleaches contain substantial amounts of chlorine in the form of [[chloride]] ions, which have no bleaching properties. Liquid bleaches sold for domestic use are typically 3&ndash;10% active chlorine, and should be diluted to 1&ndash;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. {| border="1" cellpadding="4" cellspacing="0" style="margin: 1em 1em 1em 0; background: #f9f9f9; border: 1px #aaa solid; border-collapse: collapse; font-size: 95%;" |- ! Formula ! Active chlorine |- | [[Chloride|Cl<sub>2</sub>]] | 100,0% |- | [[Sodium hypochlorite|NaClO·2½H<sub>2</sub>O]] | 59,3% |- | [[Calcium hypochlorite|Ca(ClO)<sub>2</sub>]] | 99,2% |- | [[Lithium hypochlorite|LiClO]] | 121,4% |- |} Values can be higher than 100% because [[hypochlorite]] ion have higher oxidation state (+1) than [[chlorine]](0) and so high oxidation power .</br> Percent active chlorine values have now virtually replaced the older system of [[chlorometric degree]]s: 1% active chlorine is equivalent to 3.16&nbsp;°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&nbsp;mol/Kg&nbsp;ClO<sup>&minus;</sup>(0.141 mol/L if we assume density=1). For a solid bleach, 100% active chlorine is equivalent to 14.1&nbsp;mol/kg &nbsp;ClO<sup>&minus;</sup>: [[lithium hypochlorite]] has a [[molar mass]] of 58.39&nbsp;g/mol, equivalent to 17.1&nbsp;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 [[Titration|titrating]] the [[iodine]] liberated with standard [[sodium thiosulfate]] solution. ::Cl<sub>2</sub> + 2I<sup>&minus;</sup> → I<sub>2</sub> + 2Cl<sup>&minus;</sup> or ::ClO<sup>&minus;</sup> + 2I<sup>&minus;</sup> + 2 H<sup>+</sup> → I<sub>2</sub> + H<sub>2</sub>O + Cl<sup>&minus;</sup> then ::2S<sub>2</sub>O<sub>3</sub><sup>2&minus;</sup> + I<sub>2</sub> → S<sub>4</sub>O<sub>6</sub><sup>2&minus;</sup> + 2I<sup>&minus;</sup> From the above equations it can be seen that 2&nbsp;mole of thiosulfate is equivalent to 70.9&nbsp;grams of active chlorine. [[Category:Bleaches]]