Sodium carbonate (CAS 497-19-8): storage and disposal
Anhydrous powder, decahydrate crystals and 1 M solution are the forms found in school, college, university and pathology stores. It is classified Warning for serious eye irritation only, yet it is stored with the alkalis and not with the neutral salts. The two solids behave differently over time, and a note of which one a tub contains is the first thing a collector asks.
- CAS number
- 497-19-8
- Form
- Solid
- Storage class
- Alkali
- Signal word
- Warning
- Usual EWC code
- 16 05 06*
Harmful or irritant
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
Acids are the thing to keep it away from, because acids and alkalis react with strong heat and spattering if they meet, and a carbonate fizzes as it gives off carbon dioxide, so a leaking acid bottle above a carbonate tub makes a mess quickly. Put it on a lower shelf than any acid, on its own tray, and off any shelf shared with ammonia based stock. Anhydrous powder wants a tight lid, because it takes up water from the air. A decahydrate tub is best kept closed too, and a 1 M bottle needs a name and a date written on it.
How to tell it has deteriorated
On the shelf, anhydrous powder should look dry, white and loose. If it has set into hard lumps, it has taken up water from the air. Decahydrate behaves the other way round: the clear crystals can lose water and turn into a chalky white powder, which is the same stock but no longer matches what the label implies. A crust at the cap, a stuck stopper or a bottle of 1 M solution with a white deposit at the neck points to a poor seal. Labels fade as well. Unlabelled white powder beside an old carbonate tub 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.
Before asking for a collection, note which form each container holds: anhydrous powder, decahydrate crystals or 1 M solution, and its size. The three are packed differently, and a collector needs solid and liquid listed separately. The entry for this stock is 16 05 06*, a hazardous one, so the record belongs with the other hazardous waste paperwork. It must not go into a sink, a drain, a general waste bin or a skip, and nobody should neutralise a solution with acid first. Specialist collection groups it with other alkalis, apart from acids.
| 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.
- Calcium hypochloriteSome oxidisers react strongly with alkalis, and ammonia based stock is especially at risk.
- 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.
- Nitric acidAcids and alkalis react with strong heat and spattering if they meet.
- Potassium nitrateSome oxidisers react strongly with alkalis, and ammonia based stock is especially at risk.
- Potassium permanganateSome oxidisers react strongly with alkalis, and ammonia based stock is especially at risk.
- Sulfuric acidAcids and alkalis react with strong heat and spattering if they meet.
Common quantities we collect
Usually held as: anhydrous, decahydrate, 1 M.
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
- H319 Causes serious eye irritation.
Precautionary statements
- P264+P265 Wash hands and exposed skin thoroughly after handling. Do not touch eyes.
- P280 Wear protective gloves, protective clothing, eye protection and face protection.
- P305+P351+P338 IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.
- P337+P317 If eye irritation persists: Get medical help.
Substance as classified, dilutions may differ.
Questions
Why have our washing soda crystals turned to powder?
Decahydrate crystals can lose water and become a chalky white powder, particularly in a dry cupboard. Record it as sodium carbonate in its present form, mention that the crystals have broken down, and keep the tub closed until collection.
Does unwanted 1 M sodium carbonate need a collection?
No. The classification is Warning for serious eye irritation, but the solution must not go into a sink or drain, and nobody should neutralise it first. It may be less hazardous than the solid, but it still goes for specialist collection.
Where should sodium carbonate sit on a shared shelf?
With the alkalis, below and away from any acids, and with its full name on the tub. Several white powders look alike, so check the label whenever a jar has been refilled or moved.
