Choose strength against your turnover, not your dosing rate
Sodium hypochlorite (NaOCl, CAS 7681-52-9) is sold across a wide strength range. Higher strength reduces freight per unit of available chlorine, but it also decays faster — so the right choice depends on how quickly you use it.
| Grade | Available chlorine | Typical use |
|---|---|---|
| Household | 3–6% | Domestic cleaning and laundry |
| Commercial / institutional | 6–10% | Hotels, schools, catering sanitation |
| Water treatment | 10–12% | Municipal and industrial water treatment |
| Industrial | 12–15% | Textile bleaching, pulp, wastewater |
| High-strength | 15–16% | Maximum commercial concentration |
| Food (FCC) | 5–12% | Food-contact surface sanitation |
A practical rule: if you turn stock over within two to three weeks, buy 12–15% and take the freight saving. If your consumption is slower or your store is hot, buy 10–12% and accept more freight in exchange for material that is closer to nominal strength when you use it.
Key physical properties
| Property | Value |
|---|---|
| Chemical formula | NaOCl |
| CAS number | 7681-52-9 |
| Molecular weight | 74.44 g/mol |
| Appearance | Pale greenish-yellow to clear solution |
| pH (5% solution) | 11–13 — strongly alkaline |
| Density (12–15%) | 1.17–1.21 g/cm³ |
| Stability | Decomposes before boiling; above about 35 °C decay accelerates sharply |
| Active species | Hypochlorous acid (HOCl) and hypochlorite ion (OCl⁻) |
Managing decay
Decomposition is driven by temperature, light, metal contamination and concentration. All four are controllable, and controlling them is the single biggest lever on your effective cost per kilogram of available chlorine.
- Store below 25 °C wherever possible; decay roughly doubles for each 10 °C rise, so a shaded or insulated store pays for itself
- Keep it out of direct sunlight, in opaque or dark HDPE containers
- Avoid any contact with copper, nickel, iron or cobalt — trace metals catalyse decomposition dramatically
- Buy to a schedule that matches consumption rather than stockpiling ahead of a price rise
- Test available chlorine on receipt and again before critical dosing, rather than assuming the label figure
- Rotate stock strictly first in, first out
Textile bleaching: check fibre compatibility first
Hypochlorite is an effective and inexpensive bleach for some fibres and destroys others. Getting this wrong ruins a batch rather than merely underperforming.
| Fibre | Hypochlorite suitability |
|---|---|
| Cotton | Suitable at controlled concentration and pH 10–11 |
| Linen and flax | Suitable |
| Viscose and rayon | Use with care — risk of chain scission at high concentration |
| Wool | Not suitable — attacks the keratin structure |
| Silk | Not suitable — severely damaged |
| Polyester | Not suitable — no bleaching effect and possible degradation |
| Nylon | Not suitable — yellowing and strength loss |
For wool, silk and synthetic blends, hydrogen peroxide is the appropriate bleach. Mills running mixed fibre ranges usually need both chemicals rather than one.
Materials of construction
- Suitable — HDPE, PVC, CPVC, PTFE, and titanium for demanding duty
- Not suitable — carbon steel, stainless steel, copper, brass, nickel and aluminium
- Stainless steel is the common mistake; hypochlorite pits it and the trace metal released then accelerates decomposition of the remaining stock
- Vent dosing tanks — hypochlorite slowly releases oxygen, and a sealed tank can pressurise
- Never store or dose it in any line that has carried acid, since the reaction liberates chlorine gas
What to put on the RFQ
- Available chlorine percentage at delivery, with a tolerance and preferably a guaranteed minimum on arrival
- Excess caustic (free alkali) content, which is added to stabilise the product and matters if your process is pH-sensitive
- Iron and heavy metals limits, since trace metals drive decay
- Quantity per delivery and how frequently you want deliveries — smaller and more frequent is often cheaper in effective terms
- Pack — HDPE drum, IBC or road tanker — and whether returnable
- Delivery city, and confirmation of shaded or temperature-controlled storage
- Drinking-water suitability certification if the end use is potable
What drives the price
- Chlor-alkali economics and electricity cost, as with all chlorine products
- Strength, since you are effectively buying available chlorine and shipping water
- Freight, which is a large share of delivered cost for a dilute aqueous product
- Delivery frequency — more frequent smaller deliveries cost more in freight but less in decay losses
- Season, with demand rising during monsoon and flood periods
- Exchange rate and duty on any imported material
Sourcing considerations in Pakistan
- Domestic chlor-alkali production means hypochlorite is widely available with short lead times, which supports the frequent-delivery strategy that limits decay losses
- It is a Hazard Class 8 corrosive for transport
- Ask for the manufacturing date, not just the batch number — with a product that decays, age at delivery is a legitimate purchase specification
- For potable use, retain the drinking-water suitability documentation for regulatory review