Oxalic acid (CAS 144-62-7): storage and disposal
Oxalic acid is held as white crystals, often the dihydrate, in school and college prep rooms, university labs and histology stores. It is harmful if swallowed or in contact with skin, harmful and corrosive to the eyes, and damages the kidneys if swallowed. It reacts with oxidisers and looks like many other white solids, so the label and the neighbours on the shelf decide how it is kept and collected.
- CAS number
- 144-62-7
- Form
- Solid
- Storage class
- Acid
- 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 acid 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
The dihydrate usually comes in a screw-cap jar of white crystals, and in a school prep room it often ends up near the potassium permanganate used for titrations. The two must not share a shelf, because oxalic acid reacts with oxidisers, so permanganate and its relatives belong in a separate labelled space. Keep the jar low down on an acid-resistant tray in a ventilated corrosive store, away from alkalis, and put the lid back firmly each time. Because it damages the kidneys if swallowed and is corrosive to the eyes, the jar should sit where only staff reach it, with the label facing out.
How to tell it has deteriorated
Loose, dry crystals are normal, and oxalic acid gives few visible signs of age. The faults are in the container: a perished cap, crust or powder around the neck, a cracked jar, discolouration or a label that has faded or fallen off. An unlabelled jar is the real problem, since the crystals look like many other white solids and nobody should taste, smell or test them to find out. If a jar is unlabelled or its lid has failed, leave it where it is, keep it upright and clear of oxidisers, and list it as unidentified acid solid when asking for a collection.
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 acid laboratory pack with compatible chemicals.
Crystals must never be tipped into a sink or drain, and the jar must not go out in a bin or skip. They must not be dissolved, diluted or neutralised first either. Oxalic acid is organic, so a jar outside a lab pack takes the code 16 05 08*. Record whether it is the dihydrate, roughly how much is left and whether the label is readable. The collector groups it with other organic acids and keeps it away from oxidisers such as permanganates, which is why those should be itemised separately on your inventory. Fine crystals around the neck of a jar are worth mentioning when booking.
| EWC code, laboratory chemicals | 16 05 06* |
|---|---|
| Discarded organic chemical, not a laboratory pack | 16 05 08* |
| 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
- FlammableOxidising acids can ignite flammable materials, and acid fumes attack containers and seals.
- AlkaliAcids and alkalis react with strong heat and spattering if they meet.
- OxidiserMany oxidisers release toxic gas or become unstable in contact with acid.
- ToxicToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
Named chemicals to keep apart
- AcetoneOxidising acids can ignite flammable materials, and acid fumes attack containers and seals.
- Ammonia solutionAcids and alkalis react with strong heat and spattering if they meet.
- Calcium hypochloriteMany oxidisers release toxic gas or become unstable in contact with acid.
- EthanolOxidising acids can ignite flammable materials, and acid fumes attack containers and seals.
- FormalinToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
- HexaneOxidising acids can ignite flammable materials, and acid fumes attack containers and seals.
- Hydrogen peroxideMany oxidisers release toxic gas or become unstable in contact with acid.
- Mercury(II) chlorideToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
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- MethanolOxidising acids can ignite flammable materials, and acid fumes attack containers and seals.
- Potassium hydroxideAcids and alkalis react with strong heat and spattering if they meet.
- Potassium nitrateMany oxidisers release toxic gas or become unstable in contact with acid.
- Potassium permanganateMany oxidisers release toxic gas or become unstable in contact with acid.
- Sodium cyanideToxic stock is stored apart from acids. Several toxic salts release toxic gas in contact with acid.
- Sodium hydroxideAcids and alkalis react with strong heat and spattering if they meet.
- TolueneOxidising acids can ignite flammable materials, and acid fumes attack containers and seals.
Common quantities we collect
Usually held as: solid, dihydrate.
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
- H302 Harmful if swallowed.
- H312 Harmful in contact with skin.
Precautionary statements
- P264 Wash hands and exposed skin thoroughly after handling.
- P270 Do not eat, drink or smoke when using this product.
- P280 Wear protective gloves, protective clothing, eye protection and face protection.
- P301+P317 IF SWALLOWED: Get medical help.
- P302+P352 IF ON SKIN: Wash with plenty of water.
- P317 Get medical help.
- P321 Specific treatment (see supplemental first aid instruction on this label).
- P330 Rinse mouth.
- P362+P364 Take off contaminated clothing. And wash it before reuse.
- P501 Dispose of contents and container in accordance with local, regional, national and international regulations.
Substance as classified, dilutions may differ.
Questions
Why must oxalic acid be kept away from potassium permanganate?
Oxalic acid reacts with oxidisers, and permanganate is one. Keep them in separate labelled spaces rather than on different shelves of the same cupboard. The acid goes low down in the corrosive store and the oxidiser in its own space.
What do we do with an unlabelled jar of white crystals that may be oxalic acid?
Leave the lid on and do not taste, smell or test it. Note where it was found and what the jar looks like, then list it as an unidentified solid when you ask for a collection so it can be assessed properly.
Why does a school store need to restrict access to oxalic acid?
It is harmful if swallowed, corrosive to the eyes and damages the kidneys if swallowed, and the crystals look like many other white solids. A closed cabinet with a clear label and a stock list keeps it from being mistaken for something else.
