Sodium hydroxide (CAS 1310-73-2): storage and disposal
Pellets in a school or college prep room, 0.1 M to 2 M bottles on teaching benches and stronger solution in university and histology stores account for most holdings. It is classified Danger for severe skin burns and eye damage, and it may be corrosive to metals. What decides handling is the form and strength, because a bench bottle of weak solution is not the same item as a tub of pellets or a 40% solution, and whether the cap can still be turned.
- CAS number
- 1310-73-2
- Form
- Solid
- Storage class
- Alkali
- Signal word
- Danger
- Usual EWC code
- 16 05 06*
Corrosive
What to do this week
- Check the label is readable and write down the opened date if it is not already there.
- Check it is stored as alkali stock and apart from the items listed under "Do not store with".
- If you no longer need it, add it to your disposal list so it goes on the next collection.
Safe storage in a school or lab
Pellets arrive in plastic tubs, and a tub is the right container: solutions etch glass slowly, so a glass bottle with a ground stopper can seize. Keep it away from aluminium trays and foil, because it attacks aluminium and zinc and releases hydrogen. The keep apart list that matters in a school prep room is long: aluminium powder, and every ammonium salt on the shelf above or beside it, since strong alkalis release ammonia gas from them. Acids should sit on a different level and tray. Keep the tub low, on a resistant tray, with the cap pressed on after every use.
How to tell it has deteriorated
A white crust around the neck and a cap that will not turn are the usual first signs. Pellets draw moisture and carbon dioxide from the air, so an old tub holds damp, fused pellets with a carbonate crust, sometimes set into one lump. Do not chip at it or force the cap. Solutions in glass can leave the stopper stuck, and an old bottle may show a dull, etched look inside where the glass has been attacked slowly. Corroded aluminium or zinc fittings nearby suggest the stock has been leaking. Labels attacked by caustic stain and fade, so a bottle with an unreadable strength should be recorded as unknown.
How it must be disposed of
By specialist collection only. It never goes down the drain or into general waste. It is normally packed in a corrosive alkali laboratory pack with compatible chemicals.
Never wash it away, never add acid to make it safe and never put pellets in the bin: sodium hydroxide must not go into a sink, a drain, a general waste bin or a skip, and nobody should neutralise or treat it first. A stuck cap is a note for the collector, not a job for staff to solve. Specialist collection groups it with other alkalis in strong packaging, separate from acids, and ammonium salts are kept out of the same group. Record the form, whether pellets, bench solution or the 40% stock, along with the strength and container size, and flag any tub with a crust or a seized stopper.
| EWC code, laboratory chemicals | 16 05 06* |
|---|---|
| Discarded inorganic chemical, not a laboratory pack | 16 05 07* |
| Human healthcare setting | 18 01 06* |
| Hazardous waste | Yes |
The code depends on where the waste came from and what it is mixed with. Use the waste code finder to see why.
Do not store with
- AcidAcids and alkalis react with strong heat and spattering if they meet.
- OxidiserSome oxidisers react strongly with alkalis, and ammonia based stock is especially at risk.
Named chemicals to keep apart
- Acetic acidAcids and alkalis react with strong heat and spattering if they meet.
- Aluminium powderStrong alkalis release flammable hydrogen with these metals.
- Ammonium acetateStrong alkalis release ammonia gas from ammonium salts.
- Ammonium carbonateStrong alkalis release ammonia gas from ammonium salts.
- Ammonium chlorideStrong alkalis release ammonia gas from ammonium salts.
- Ammonium nitrateStrong alkalis release ammonia gas from ammonium salts.
- Ammonium oxalateStrong alkalis release ammonia gas from ammonium salts.
- Ammonium sulfateStrong alkalis release ammonia gas from ammonium salts.
Show 15 more
- Ammonium thiocyanateStrong alkalis release ammonia gas from ammonium salts.
- Calcium carbideReacts with water, releasing heat and often a flammable or corrosive gas, so keep it away from all water based stock.
- Calcium hypochloriteSome oxidisers react strongly with alkalis, and ammonia based stock is especially at risk.
- Calcium metalReacts with water, releasing heat and often a flammable or corrosive gas, so keep it away from all water based stock.
- ChloroformChloroform can react violently with strong alkalis, especially when acetone is present.
- Hydrochloric acidAcids and alkalis react with strong heat and spattering if they meet.
- Hydrogen peroxideSome oxidisers react strongly with alkalis, and ammonia based stock is especially at risk.
- Lithium aluminium hydrideReacts with water, releasing heat and often a flammable or corrosive gas, so keep it away from all water based stock.
- Lithium metalReacts with water, releasing heat and often a flammable or corrosive gas, so keep it away from all water based stock.
- Nitric acidAcids and alkalis react with strong heat and spattering if they meet.
- Potassium metalReacts with water, releasing heat and often a flammable or corrosive gas, so keep it away from all water based stock.
- Sodium hydrideReacts with water, releasing heat and often a flammable or corrosive gas, so keep it away from all water based stock.
- Sodium metalReacts with water, releasing heat and often a flammable or corrosive gas, so keep it away from all water based stock.
- Tin metalStrong alkalis release flammable hydrogen with these metals.
- Zinc powderStrong alkalis release flammable hydrogen with these metals.
Common quantities we collect
Usually held as: pellets, 0.1 M, 1 M, 2 M, 40% solution.
Part-used bottles and full containers are both fine. Tell us the size and how many, and an estimate is enough for a first price.
Where it is commonly held
Hazard statements
- H290 May be corrosive to metals.
- H314 Causes severe skin burns and eye damage.
Precautionary statements
- P260 Do not breathe dust, fume, gas, mist, vapours or spray.
- P264 Wash hands and exposed skin thoroughly after handling.
- P280 Wear protective gloves, protective clothing, eye protection and face protection.
- P301+P330+P331 IF SWALLOWED: Rinse mouth. Do NOT induce vomiting.
- P302+P361+P354 IF ON SKIN: Take off immediately all contaminated clothing. Immediately rinse with water for several minutes.
- P304+P340 IF INHALED: Remove person to fresh air and keep comfortable for breathing.
- P305+P354+P338 IF IN EYES: Immediately rinse with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.
- P316 Get emergency medical help immediately.
- P321 Specific treatment (see supplemental first aid instruction on this label).
- P363 Wash contaminated clothing before reuse.
- P405 Store locked up.
- P501 Dispose of contents and container in accordance with local, regional, national and international regulations.
- P234 Keep only in original packaging.
- P264+P265 Wash hands and exposed skin thoroughly after handling. Do not touch eyes.
- P302+P352 IF ON SKIN: Wash with plenty of water.
- P305+P351+P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.
- P317 Get medical help.
- P332+P317 If skin irritation occurs: Get medical help.
- P337+P317 If eye irritation persists: Get medical help.
- P362+P364 Take off contaminated clothing. And wash it before reuse.
- P390 Absorb spillage to prevent material damage.
- P406 Store in corrosive resistant container with a resistant inner liner.
Substance as classified, dilutions may differ.
Questions
The cap on our sodium hydroxide tub is stuck. What should we do?
Leave it closed and do not force it or chip at the crust. Carbonate builds up around the thread when the stock has taken carbon dioxide from the air. Record the tub, keep it low on its tray and tell the collector it has a stuck cap when you book.
Can weak 0.1 M solution be thrown away on site?
No. Even bench strength solution should not go into a sink or drain, and nobody should neutralise it first. It may be less hazardous than pellets or the 40% stock, but that is not something to assume, and it still goes for specialist collection.
Why not store it next to ammonium chloride?
Strong alkalis release ammonia gas from ammonium salts, so a leaking cap or a spill near an ammonium shelf can release ammonia gas into the cupboard. Keep ammonium salts on a separate shelf from the alkalis, with a tray under each.
How should a 40% sodium hydroxide bottle be recorded for collection?
Write the strength, volume, container material and any crust or leak. A stronger stock bottle is described differently from bench strength solution, and the collector needs that to group it with other alkalis rather than with acids.
