Calcium hypochlorite formula and names
The chemical formula of calcium hypochlorite is Ca(OCl)2, also written Ca(ClO)2 or CaCl2O2: one calcium ion (Ca2+) balanced by two hypochlorite ions (OCl−). Its molar mass is 142.98 g/mol. It is the calcium salt of hypochlorous acid and is the solid counterpart of liquid bleach, sodium hypochlorite.
| Item | Value |
|---|---|
| Formula | Ca(OCl)2 (CaCl2O2) |
| Molar mass | 142.98 g/mol |
| CAS number | 7778-54-3 |
| EC number | 231-908-7 |
| Other names | Calcium oxychloride, hypochlorous acid calcium salt |
| HS code (6-digit) | 2828.10 (commercial calcium hypochlorite and other calcium hypochlorites) |
| UN number (dry, over 39% available chlorine) | UN 1748 |
The molar mass follows from the atomic masses: 40.078 (calcium) + 2 × 35.453 (chlorine) + 2 × 15.999 (oxygen) = 142.98 g/mol. In the US tariff the line is 2828.10.00; confirm your national tariff line with your customs broker.
Available chlorine and grades
Calcium hypochlorite is sold by its available chlorine: its oxidising power, expressed as the equivalent weight of chlorine gas (Cl2). Each hypochlorite ion does the same oxidising work as one Cl2 molecule, so pure Ca(OCl)2 has a theoretical available chlorine of 2 × 70.90 ÷ 142.98 = 99.2%. HSDB lists exactly this figure for the high-purity material, and 70% for the commercial grade.
| Product | Available chlorine | Notes |
|---|---|---|
| Calcium hypochlorite granules | Commonly 65–70% | White granules or powder; the main commercial form |
| Calcium hypochlorite tablets | Same material | Compressed from the granules |
| Bleaching powder (chlorinated lime) | At least 30% | A mixture of calcium hypochlorite, calcium chloride and calcium hydroxide |
| Pure calcium hypochlorite | 99.2% (theoretical) | Reference value, not a trade grade |
HSDB warns that bleaching powder should not be confused with pure calcium hypochlorite. It is less stable, losing much of its activity over a year even as a solid, so check the date of manufacture as well as the available chlorine on the Certificate of Analysis (CoA).
Appearance and properties
Calcium hypochlorite is a white solid, sold as granules, powder or tablets, with a strong chlorine odour. Values below are from the International Chemical Safety Card (ICSC 0638), NOAA’s CAMEO Chemicals database and HSDB.
| Property | Value |
|---|---|
| Appearance | White granules, powder or tablets; strong chlorine odour |
| Density | 2.35 g/cm3 |
| Solubility in water | 21 g per 100 mL at 25 °C |
| On heating | Decomposes (from about 100 °C; rapidly above 175 °C), releasing oxygen and chlorine |
| In water | The solution is a medium strong base |
| Fire behaviour | Not combustible, but a strong oxidiser that makes other materials burn more fiercely |
HSDB notes that the 70% grade may decompose violently if exposed to heat or direct sunlight, and NOAA reports that it slowly decomposes in water and moist air. Heat and moisture are therefore the two things to keep away from it in storage.
How calcium hypochlorite is made
HSDB describes the main industrial route: a slurry of lime and caustic soda is chlorinated, calcium hypochlorite dihydrate crystallises out, and the filter cake is dried under vacuum. Bleaching powder is made more simply, by saturating slaked lime (calcium hydroxide) with chlorine. In simplified form, the chlorination of lime is:
2Ca(OH)2 + 2Cl2 → Ca(OCl)2 + CaCl2 + 2H2O
The calcium chloride and unreacted lime left in bleaching powder are why its available chlorine is lower than that of refined calcium hypochlorite.
What calcium hypochlorite is used for
HSDB and Haz-Map list these main uses:
- Drinking water: disinfecting potable water supplies.
- Swimming pools: pool sanitation and algae control, often as granules or tablets.
- Bleaching: as a bleaching agent for paper pulp and textiles.
- Sanitation: as a household and industrial sanitiser and disinfectant, and to control mildew.
- Wastewater: in sewage and wastewater treatment.
Compared with sodium hypochlorite (liquid bleach), the solid carries far more available chlorine per kilogram, which suits long-distance shipping and sites without bulk liquid storage. Treatment doses depend on the water and on local health rules, so follow the standards that apply to your application.
Hazards, storage and transport
Calcium hypochlorite is both a strong oxidiser and a corrosive substance. Its EU harmonised classification is oxidising solid category 2 (H272, may intensify fire), acute toxicity category 4 (H302, harmful if swallowed), skin corrosion category 1B (H314) and acute aquatic hazard category 1 (H400, very toxic to aquatic life).
- Never mix it with other chemicals. The ICSC warns that it decomposes rapidly on contact with acids, releasing chlorine, and reacts violently with ammonia, amines and other nitrogen compounds, and with combustible and reducing materials. Keep it away from acids, other pool chemicals, oils, solvents and organic matter.
- Health: it is corrosive to the eyes, skin and respiratory tract. Breathing in decomposition products can cause lung oedema, and the ICSC notes that the effects may be delayed.
- Fire: it does not burn, but it releases oxygen as it decomposes, so smothering a fire does not work. HSDB and the ICSC advise large amounts of water, and no dry-powder extinguishers.
- Environment: it is very toxic to aquatic organisms and must not reach drains or waterways.
The ICSC advises preventing dust, using local exhaust or breathing protection, and wearing gloves, protective clothing and a face shield. For first aid, move the person to fresh air and get medical attention; remove contaminated clothing and rinse the skin with plenty of water; rinse eyes for several minutes and get medical attention; and, if swallowed, rinse the mouth and give one or two glasses of water without inducing vomiting. Rinse contaminated clothing with plenty of water, because it is a fire hazard when dry.
For storage, HSDB advises a cool, dry, well-ventilated place below 50 °C, separated from acids, ammonia, amines, other chlorinating agents and oxidising materials. The ICSC adds: keep containers well closed, separate from food and feedstuffs, in an area without drain or sewer access.
All calcium hypochlorite transport entries are in Class 5.1 (oxidising substances), under ERG Guide 140. The entry depends on the available chlorine and water content:
| UN number | Entry |
|---|---|
| UN 1748 | Calcium hypochlorite, dry, or mixture, dry, with more than 39% available chlorine; Class 5.1, packing group II (ICSC) |
| UN 2208 | Calcium hypochlorite mixture, dry, with more than 10% but not more than 39% available chlorine; Class 5.1 |
| UN 2880 | Calcium hypochlorite, hydrated, with 5.5% to 16% water; Class 5.1 |
| UN 3485, 3486, 3487 | Corrosive versions of the three entries above; Class 5.1 with a corrosive label |
Check section 14 of the current SDS for the exact entry for your grade, and confirm packing and labels with your freight forwarder.
Questions to ask a supplier
- What is the guaranteed minimum available chlorine, and how is it tested?
- Is the product dry or hydrated, and which UN entry applies to it?
- What is the date of manufacture, and what shelf life do you state?
- Can you share a recent Certificate of Analysis and the current SDS for this grade?
- What packing do you offer, is it UN-approved for Class 5.1, and how is it protected from moisture?
Enquire with Scapex Exports
Scapex Exports is an exporter and supplier of industrial and water treatment chemicals from India. Our calcium hypochlorite 65–70% page lists the grade and packing and links to its COA and MSDS. We also list calcium hypochlorite tablets, bleaching powder and sodium hypochlorite solution.
Tell us the form, available chlorine, quantity, packing and destination port, and we will reply with a quotation.
Frequently asked questions
What is the formula of calcium hypochlorite?
Ca(OCl)2, also written Ca(ClO)2. Its molar mass is 142.98 g/mol and its CAS number is 7778-54-3.
Is calcium hypochlorite the same as bleaching powder?
No. Bleaching powder is a mixture of calcium hypochlorite, calcium chloride and calcium hydroxide with at least 30% available chlorine. Commercial calcium hypochlorite is far stronger, at about 65 to 70%.
What does 70% available chlorine mean?
It expresses the product’s oxidising power as an equivalent weight of chlorine. Pure calcium hypochlorite would be 99.2%, so a 70% grade is roughly 70% calcium hypochlorite.
What is calcium hypochlorite used for?
Mainly for disinfecting drinking water and swimming pools, for bleaching paper pulp and textiles, and as a sanitiser and disinfectant.
Is calcium hypochlorite dangerous?
Yes. It is a strong oxidiser and corrosive, and it reacts dangerously with acids, ammonia and organic materials. It is shipped in Class 5.1, for example as UN 1748.
Sources: ILO/WHO International Chemical Safety Card ICSC 0638, calcium hypochlorite; NOAA CAMEO Chemicals datasheets for calcium hypochlorite and its UN entries; HSDB, Haz-Map, ECHA and EU CLP records for calcium hypochlorite via PubChem; US Harmonized Tariff Schedule, subheading 2828.10.