Percent active chlorine
Encyclopedia
Percent active chlorine is a unit of concentration
used for 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 3–10% 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) than chlorine
(0) and so high oxidation power .
Percent active chlorine values have now virtually replaced the older system of chlorometric degrees: 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 a molar 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
the iodine
liberated with standard sodium thiosulfate
solution.
or
then
From the above equations it can be seen that 2 mole of thiosulfate is equivalent to 70.9 grams of active chlorine.
Concentration
In chemistry, concentration is defined as the abundance of a constituent divided by the total volume of a mixture. Four types can be distinguished: mass concentration, molar concentration, number concentration, and volume concentration...
used for hypochlorite
Hypochlorous acid
Hypochlorous acid is a weak acid with the chemical formula HClO. It forms when chlorine dissolves in water. It cannot be isolated in pure form due to rapid equilibration with its precursor...
-based bleach
Bleach
Bleach refers to a number of chemicals that remove color, whiten, or disinfect, often via oxidation. Common chemical bleaches include household chlorine bleach , lye, oxygen bleach , and bleaching powder...
es. One gram of a 100% active chlorine bleach has the same bleaching power as one gram of chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
. The term "active chlorine" is used because most commercial bleaches contain substantial amounts of chlorine in the form of chloride
Chloride
The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water...
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.
| Formula | Active chlorine |
|---|---|
| Cl2 Chloride The chloride ion is formed when the element chlorine, a halogen, picks up one electron to form an anion Cl−. The salts of hydrochloric acid HCl contain chloride ions and can also be called chlorides. The chloride ion, and its salts such as sodium chloride, are very soluble in water... |
100.0% |
| NaClO·2½H2O | 59.3% |
| Ca(ClO)2 Calcium hypochlorite Calcium hypochlorite is a chemical compound with formula 2. It is widely used for water treatment and as a bleaching agent... |
99.2% |
| LiClO Lithium hypochlorite Lithium hypochlorite is the colorless, crystalline lithium salt of hypochlorous acid with the chemical formula of LiClO. It is used as a disinfectant for pools and a reagent for some chemical reactions.-Safety:... |
121.4% |
Values can be higher than 100% because hypochlorite
Hypochlorite
The hypochlorite ion, also known as chlorate anion is ClO−. A hypochlorite compound is a chemical compound containing this group, with chlorine in oxidation state +1.Hypochlorites are the salts of hypochlorous acid...
ion have higher oxidation state (+1) than chlorine
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
(0) and so high oxidation power .
Percent active chlorine values have now virtually replaced the older system of chlorometric degrees: 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
Lithium hypochlorite
Lithium hypochlorite is the colorless, crystalline lithium salt of hypochlorous acid with the chemical formula of LiClO. It is used as a disinfectant for pools and a reagent for some chemical reactions.-Safety:...
has a molar mass
Molar mass
Molar mass, symbol M, is a physical property of a given substance , namely its mass per amount of substance. The base SI unit for mass is the kilogram and that for amount of substance is the mole. Thus, the derived unit for molar mass is kg/mol...
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
Potassium iodide
Potassium iodide is an inorganic compound with the chemical formula KI. This white salt is the most commercially significant iodide compound, with approximately 37,000 tons produced in 1985. It is less hygroscopic than sodium iodide, making it easier to work with...
to a sample of bleach solution and titrating
Titration
Titration, also known as titrimetry, is a common laboratory method of quantitative chemical analysis that is used to determine the unknown concentration of an identified analyte. Because volume measurements play a key role in titration, it is also known as volumetric analysis. A reagent, called the...
the iodine
Iodine
Iodine is a chemical element with the symbol I and atomic number 53. The name is pronounced , , or . The name is from the , meaning violet or purple, due to the color of elemental iodine vapor....
liberated with standard sodium thiosulfate
Sodium thiosulfate
Sodium thiosulfate , also spelled sodium thiosulphate, is a colorless crystalline compound that is more familiar as the pentahydrate, Na2S2O3•5H2O, an efflorescent, monoclinic crystalline substance also called sodium hyposulfite or “hypo.”...
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.