Bleach is one of the most searched chemicals on the internet and one of the most routinely mis-specified in industrial purchasing. The questions consumers ask about it — is it flammable, is it an acid, what is its pH — have precise answers that also happen to determine how it is stored, shipped and dosed on a plant. This article answers them, then covers the grades, stability behaviour and handling requirements that matter when you are buying by the drum, IBC or tanker.
What bleach actually is: the chemical formula
Liquid bleach is an aqueous solution of sodium hypochlorite.
- Formula: NaOCl (equivalently written NaClO)
- CAS number: 7681-52-9
- Molar mass: 74.44 g/mol
- Synonyms: hypochlorite solution, liquid chlorine bleach, soda bleach liquor
The solid, anhydrous compound is unstable and is not an article of commerce. Every product sold as bleach is a solution, and it is never just hypochlorite in water. It also contains sodium chloride (a by-product of manufacture, made by absorbing chlorine gas into caustic soda) and a deliberate excess of sodium hydroxide, which is there for stability rather than for cleaning performance.
The distinction that matters commercially is strength. Household bleach is typically 3–6% available chlorine. Industrial and commercial grades run 10–15% and above. They are the same chemistry at very different concentration, and they behave differently on storage, on corrosion and on hazard classification.
Note also the two conventions used to express strength. Trade documents may quote % w/w sodium hypochlorite, % available chlorine, or grams per litre available chlorine. They are not the same number. One per cent NaOCl by weight corresponds to roughly 0.95% available chlorine, and a typical 12.5% w/w solution at a density near 1.20 g/mL is around 150 g/L available chlorine. Always confirm which basis an offer is written on before comparing prices or setting a dosing rate.
Is bleach flammable?
No. Sodium hypochlorite solution is not flammable. It is mostly water, it has no flash point, and it will not ignite or sustain combustion.
That answer, on its own, is misleading. Bleach is a strong oxidiser, and an oxidiser presents a hazard that is different in kind from a flammable liquid — and in a warehouse setting, arguably a more serious one.
A fire needs fuel, heat and an oxygen source. Flammable liquids supply the fuel. Oxidisers supply the oxygen, chemically, from within the material itself. Hypochlorite does not burn, but it can release oxygen to a fire that is already burning in adjacent combustibles, raising the temperature and the burn rate, and allowing materials to keep burning in conditions where they otherwise would not. Contact with organic materials, reducing agents, or incompatible chemicals can start or intensify a fire without any external ignition source at all.
The practical control is segregation. Hypochlorite must be stored away from fuels, solvents, oils, rags and other combustible or reducing materials, and away from acids.
The mixtures that must be avoided
Two incompatibilities cause the majority of real-world hypochlorite injuries, and both are worth stating plainly as warnings.
- Never allow contact with acids. Any acid — including descalers, toilet cleaners and acidic effluent — will liberate chlorine gas, a severe respiratory poison. This is why hypochlorite drums must never be stored above or adjacent to acid drums, why dosing lines must not be shared, and why bunds must not be common. Safety data sheets carry the hazard statement "contact with acids liberates toxic gas" for exactly this reason.
- Never allow contact with ammonia or ammonium salts. The reaction forms chloramines, which are irritant and toxic to the respiratory tract. This includes ammoniacal cleaning products and ammonia-bearing process streams.
Mixing with other chemical products generally, including reducing agents such as sulphites and thiosulphate (which react vigorously), should be treated as prohibited unless the reaction is a designed, engineered process step under controlled conditions.
Is bleach acidic or basic, and what is its pH?
Bleach is basic. It is not an acid, and it never has been.
Two things make it alkaline. First, hypochlorite is the conjugate base of hypochlorous acid, a weak acid with a pKa of approximately 7.5 at 25 °C. Dissolved hypochlorite therefore hydrolyses in water to give an alkaline solution. Second, and more significantly for commercial product, manufacturers add an excess of sodium hydroxide on purpose.
Typical values:
| Product | Available chlorine | Typical pH |
|---|---|---|
| Household bleach | 3–6% | ~11–13 |
| Commercial/industrial solution | 10–15% | ~12.5–13.5 or higher |
Why hypochlorite is deliberately buffered alkaline
Free alkali is a stabiliser, not a contaminant. Hypochlorite solutions decompose faster as pH falls, and the decomposition pathway shifts toward chlorate formation in the mid-pH region. Holding the solution strongly alkaline suppresses both effects and keeps available chlorine in the drum for longer. Commercial grades therefore carry a specified free alkali, expressed as NaOH, usually somewhere in the range of roughly 0.5–1.5% w/w for industrial strengths, with higher-strength material generally carrying more.
There is a trade-off. Too little free alkali and the product decays quickly; too much adds unwanted caustic load to the treated stream and can cause scaling or pH excursions in a dosing application. If free alkali matters to your process, put a range on it in the specification rather than accepting whatever arrives.
What happens to the equilibrium as pH drops
At the point of use, the disinfecting species matters more than the label strength. In water, hypochlorite and hypochlorous acid exist in equilibrium:
HOCl ⇌ H⁺ + OCl⁻
Hypochlorous acid (HOCl) is substantially the more effective biocide of the two. Because the pKa is around 7.5:
- At pH 6–7, the balance favours HOCl and disinfection is most efficient.
- At around pH 7.5, the two forms are roughly equal.
- Above pH 9, the solution is essentially all hypochlorite ion, which is a much weaker disinfectant.
This is the reason a water treatment plant that lets pH drift upward sees chlorine demand rise even though dosing has not changed. The concentrated product is stored alkaline for stability; the treated water needs to sit in a lower pH band for efficacy. Those are two separate control problems and both belong in the process design.
Stability and decomposition: the real procurement issue
Sodium hypochlorite is a decaying product. Available chlorine falls from the moment of manufacture, by two routes:
- Disproportionation to chlorate: 3 NaOCl → NaClO₃ + 2 NaCl. This consumes available chlorine and builds chlorate, which is a regulated impurity in drinking water applications.
- Catalytic decomposition to oxygen: 2 NaOCl → 2 NaCl + O₂. This is accelerated dramatically by traces of transition metals — nickel, copper, cobalt, iron and manganese — and produces gas, which is why storage vessels must be vented and why dosing pumps can vapour-lock on gassing product.
The rate is governed by four variables:
- Concentration. Stronger solutions decay disproportionately faster. A 15% product will not hold its assay as well as a 10% product under identical conditions.
- Temperature. The dominant factor. Decomposition rises steeply with temperature; a consignment sitting in a metal container in a tropical port loses assay far faster than the same drums in a shaded, ventilated store.
- Light. UV drives photolytic decomposition. Product must be kept in opaque packaging and out of direct sunlight.
- Metal contamination. Ppm-level transition metal ingress from process water, packaging or transfer equipment will shorten shelf life measurably.
This is why "available chlorine on despatch" and "available chlorine on arrival" are different numbers. A certificate of analysis records the strength at the time of test at the loading point. By the time a container has sat at a port, crossed an ocean and cleared customs, the material has been decaying continuously for weeks. Contracts written on a single assay figure with no reference point create disputes; contracts that state the assay basis, the reference date and an agreed tolerance on arrival do not. Buyers commonly manage this by specifying a small overage at despatch, or by nominating the acceptance assay explicitly.
Commercial grades and specifications
Grades traded internationally, with indicative parameters:
| Grade | Available chlorine | Typical free alkali (as NaOH) | Appearance | Typical applications |
|---|---|---|---|---|
| Household / consumer dilution | 3–6% | Low | Clear pale yellow liquid | Domestic cleaning, laundry, general sanitation |
| Commercial general purpose | 8–10% | ~0.5–1.0% | Pale greenish-yellow liquid | Building sanitation, laundry, pools |
| Standard industrial | 10–12% | ~0.5–1.5% | Pale greenish-yellow liquid | Municipal water, effluent treatment, CIP |
| High strength industrial | 13–15% | ~0.8–1.5% | Deeper greenish-yellow liquid | Bulk water treatment, chemical synthesis, scrubbing |
| Potable-water grade | Typically 10–15% | Per applicable standard | Clear, low turbidity | Drinking water treatment |
| Calcium hypochlorite (solid alternative) | 65–70% | Not applicable | White granules or tablets | Pools, remote sites, long-transit export |
Potable-water grade is distinguished less by strength than by impurity control — tight limits on chlorate, bromate, perchlorate and heavy metals, and conformity to a recognised standard such as EN 901 or NSF/ANSI 60. If the end use is drinking water, name the standard in the enquiry; it changes the source, the caustic feedstock and the testing regime.
Industrial applications
- Municipal and industrial water disinfection. The most common application by volume, and the safest practical substitute for gaseous chlorine at small and medium plants.
- CIP and sanitation in food, beverage and dairy. Used as a sanitising step in clean-in-place cycles, usually at controlled low concentration and with careful attention to rinse and to stainless steel contact time.
- Textile bleaching. Cotton and cellulosic bleaching, though peroxide has displaced hypochlorite in many mills for fibre-damage reasons.
- Pulp and paper. Historically a bleaching stage; now largely displaced by chlorine dioxide and peroxide in ECF sequences, with residual use in specific stages and in hypochlorite-based brightening.
- Effluent and wastewater treatment. Disinfection of treated effluent, odour control, sulphide oxidation, and alkaline chlorination for cyanide destruction in metal finishing waste.
- Swimming pools and recreational water. Both as liquid dosing and, where a solid is preferred, as calcium hypochlorite.
- Gas scrubbing. Hypochlorite scrubbing liquors for hydrogen sulphide and odorous vent streams.
Handling, storage, materials of construction and transport
Materials of construction. Hypochlorite is aggressive to most metals. Suitable: HDPE, PVC, CPVC, PVDF, PTFE, and correctly specified FRP with a chemically resistant liner. Titanium performs well. Avoid: mild steel, stainless steel (pitting and chloride stress corrosion cracking), copper, brass, bronze, aluminium and nickel alloys. Gaskets and diaphragms should be selected for oxidiser service; many common elastomers degrade.
Storage. Cool, shaded, well ventilated, out of direct sunlight, bunded, and segregated from acids, ammonia, reducing agents and combustibles. Tanks and drums must be vented, because decomposition generates oxygen and pressure will build in a sealed vessel. Stock should be rotated strictly first-in-first-out and assayed before use if it has been held for any length of time.
PPE. Chemical splash goggles or face shield, chemical-resistant gloves and apron or suit, and closed footwear. Handle in ventilated areas; provide eyewash and safety shower at transfer points. Never decant into unlabelled containers, and never into a container that has held an acid.
Classification and transport. Sodium hypochlorite solution ships under UN 1791, Class 8 (corrosive), with packing group assigned according to concentration — commonly PG II for industrial strengths and PG III for weaker solutions. Hypochlorite solutions are typically classified as marine pollutants under IMDG because of their aquatic toxicity, which affects documentation and marking. Under GHS, industrial-strength material is generally classified as skin corrosive and seriously damaging to eyes, hazardous to the aquatic environment, and carries the supplemental statement regarding release of toxic gas on contact with acids. Confirm the exact classification against the current supplier SDS and the edition of the regulations in force for your route.
Buying sodium hypochlorite for export
An enquiry that can be quoted accurately states:
- Available chlorine, with the basis stated (% w/w NaOCl, % available chlorine, or g/L) and whether it applies at despatch or on arrival
- Free alkali as NaOH, with a range
- Impurity limits where relevant — chlorate, bromate, perchlorate, iron, nickel, copper — and any standard the product must meet
- Application and end use, since potable water, food contact and general industrial use are sourced differently
- Packing: 25–35 kg HDPE carboys or jerricans, 200–250 L HDPE drums, 1,000 L IBCs, or bulk
- Destination port, expected transit time and season, which govern how the decay allowance is set
- Whether UN-approved packaging and full dangerous goods documentation are required
The transit point is the one buyers most often overlook. Shipping a decaying oxidiser across an ocean is a different problem from buying it locally. Transit time, container temperature, sun exposure on deck and dwell time at transhipment ports all consume available chlorine before the drums reach the plant. Long routes and hot seasons argue for a despatch overage, opaque packaging, shaded stowage where the line allows it, and a realistic acceptance tolerance written into the contract rather than negotiated after arrival.
When calcium hypochlorite is the better answer
Where transit is long, storage conditions cannot be controlled, or the freight cost of shipping 85–90% water is unattractive, calcium hypochlorite is often the more sensible product. As a solid at 65–70% available chlorine, it is far more stable in storage and much denser in shipped chlorine per tonne of freight.
- Formula: Ca(ClO)₂ | CAS: 7778-54-3
- Transport: UN 1748 (dry), Class 5.1 oxidiser; hydrated forms ship under UN 2880
The trade-off is that calcium hypochlorite is classified as an oxidising solid with its own strict storage rules, it adds calcium hardness to the treated water, and it requires dissolution equipment. It is not a drop-in substitute, but for remote sites, island markets and long lead-time supply chains it frequently works out better than liquid.
Enquiries
Sodium hypochlorite and calcium hypochlorite are supplied by Scapex Exports from qualified Indian manufacturers, with grade, packing and documentation set against the buyer's specification rather than a fixed catalogue. Send the available chlorine basis, free alkali requirement, end use, destination port and preferred packing, and the enquiry can be quoted against the correct grade and the correct decay allowance for the route.
Frequently asked questions
What is the chemical formula for bleach?
Household and industrial liquid bleach is an aqueous solution of sodium hypochlorite, formula NaOCl (also written NaClO), CAS number 7681-52-9. The product is never pure hypochlorite; it is hypochlorite dissolved in water together with sodium chloride and a deliberate excess of sodium hydroxide.
Is bleach flammable?
No. Sodium hypochlorite solution is water-based and will not ignite or sustain a flame. It is, however, a strong oxidiser, which means it can supply oxygen to a fire involving other materials and make that fire burn hotter and faster than it otherwise would.
Is bleach acidic or basic?
Bleach is basic (alkaline). Hypochlorite is the conjugate base of a weak acid, and commercial solutions also carry free sodium hydroxide, so they sit well into the alkaline range. Bleach is not an acid, and contact with acids must be avoided because it releases toxic chlorine gas.
What is the pH of bleach?
Household bleach at 3–6% available chlorine typically measures around pH 11 to 13. Industrial grades at 10–15% are usually higher, commonly pH 12.5 to 13.5 or above, because they contain more excess caustic to hold the hypochlorite stable.
How long does sodium hypochlorite last in storage?
It decomposes continuously, so available chlorine falls from the day of manufacture. Losses accelerate sharply with temperature, exposure to light and traces of transition metals, which is why an assay measured on despatch will not match the assay on arrival after a long sea voyage.