Skip to content

Chemical collection and stock control for UK schools, universities and hospitals

Potassium dichromate (CAS 7778-50-9): storage and disposal

Orange crystals of potassium dichromate, and 0.1 M solutions, are familiar in school, college and university prep rooms, and histology labs may hold it as well. It may cause cancer and genetic defects, may damage fertility, is fatal if inhaled and is a skin and respiratory sensitiser. Its chromium(VI) content decides the handling of the solid. For a solution bottle, what matters is how far it has dried at the neck and whether organic matter has reached it.

CAS number
7778-50-9
Form
Solid
Storage class
Oxidiser
Signal word
Danger
Usual EWC code, laboratory stock
16 05 06*
  • Oxidising pictogramOxidising
  • Corrosive pictogramCorrosive
  • Acute toxicity pictogramAcute toxicity
  • Serious health hazard pictogramSerious health hazard
  • Hazardous to the environment pictogramHazardous to the environment

What to do this week

  1. Without moving anything that looks damaged, check the label is readable and write down the opened date if it is not already there.
  2. Check it is stored as oxidiser stock, and apart from anything listed under "Do not store with" on this page. If nothing is listed, that does not prove it is safe with everything.
  3. If you no longer need it, add it to your disposal list so it can be included in a collection.

Safe storage in a school or lab

Check the stopper of the 0.1 M bottle for a dry orange crust. Water evaporating at the neck leaves crystals, and twisting the stopper can turn them to dust, which is the worst way to meet this salt given that it is fatal if inhaled. Both solid and solution belong in the labelled oxidiser space, on non-combustible shelving where possible. Glucose, activated charcoal, aluminium powder, diethyl ether and hydrazine hydrate all need to be elsewhere. In histology, it should not sit on the staining bench among alcohols and xylene. A weaker solution may be less hazardous than the solid, but it still needs its strength and date on the label. Anyone with a known skin or chest reaction should not be the one handling it.

How to tell it has deteriorated

Healthy solid is bright orange, dry and free running, and unlike the sodium salt it takes up little moisture. A wet look therefore suggests a leak or water from outside. A green tinge shows reduction to chromium(III), usually from contamination by organics such as a dirty spatula, paper or a stray drop of alcohol. The 0.1 M solution should be clear orange, so a green or brownish tint or a sediment points the same way. An orange crust on the neck is common and needs care because of the dust. Green does not mean the hazard has gone, as chromium(VI) normally remains alongside it. Do not chip at crusts or stir the contents. Leave it closed and write down what you see.

How it is disposed of

We arrange this by specialist collection. We do not publish a drain or general waste route for any chemical. It is normally packed in an oxidising laboratory pack with compatible chemicals.

Code 16 05 06* is the usual one for school and university stock, and 18 01 06* for a hospital histology lab. The asterisk marks it as hazardous, which matters for the 0.1 M bottle as much as for the solid: a weak looking solution must not go into a sink, a drain, a general waste bin or a skip, and nobody should try to treat it first. Specialist collection is the only route. In the collection it travels as an oxidiser, grouped away from solvents and other organics. Record whether you hold the solid or a solution, the strength, any green tinge and what else a used solution may contain, such as staining residues. Used and unused stock should be listed separately.

Waste codes for Potassium dichromate
Usual EWC code, laboratory stock16 05 06*
Discarded inorganic chemical, not a laboratory pack16 05 07*
Human healthcare setting18 01 06*
Usually classed as hazardous wasteYes

The code depends on where the waste came from and what it contains, and classifying it is the producer's duty. Use the waste code finder to see why.

Do not store with

  • FlammableOxidisers can ignite flammable materials or make a fire far more intense.
  • AcidMany oxidisers release toxic gas or become unstable in contact with acid.
  • AlkaliSome oxidisers react strongly with alkalis, and ammonia based stock is especially at risk.
  • ToxicToxic and oxidising stock are stored apart. A reaction could release toxic vapours.
  • CorrosiveCorrosive stock can react with oxidisers, releasing heat or fumes.

Named chemicals to keep apart

  • 1,2-DimethoxyethanePeroxide forming ethers can ignite or explode with strong oxidisers.
  • 1,4-DioxanePeroxide forming ethers can ignite or explode with strong oxidisers.
  • Acetic acidMany oxidisers release toxic gas or become unstable in contact with acid.
  • AcetoneOxidisers can ignite flammable materials or make a fire far more intense.
  • Aluminium powderStrong oxidisers can form mixtures with these materials that burn fiercely or explode.
  • Ammonia solutionSome oxidisers react strongly with alkalis, and ammonia based stock is especially at risk.
  • Diethyl etherPeroxide forming ethers can ignite or explode with strong oxidisers.
  • Diisopropyl etherPeroxide forming ethers can ignite or explode with strong oxidisers.
Show 15 more
  • EthanolOxidisers can ignite flammable materials or make a fire far more intense.
  • FormalinToxic and oxidising stock are stored apart. A reaction could release toxic vapours.
  • GlucoseStrong oxidisers can form mixtures with these materials that burn fiercely or explode.
  • HexaneOxidisers can ignite flammable materials or make a fire far more intense.
  • Hydrochloric acidMany oxidisers release toxic gas or become unstable in contact with acid.
  • Iron filingsStrong oxidisers can form mixtures with these materials that burn fiercely or explode.
  • Magnesium ribbonStrong oxidisers can form mixtures with these materials that burn fiercely or explode.
  • Potassium cyanideCyanides react violently with strong oxidisers.
  • Red phosphorusStrong oxidisers can form mixtures with these materials that burn fiercely or explode.
  • Sodium cyanideCyanides react violently with strong oxidisers.
  • SucroseStrong oxidisers can form mixtures with these materials that burn fiercely or explode.
  • SulfurStrong oxidisers can form mixtures with these materials that burn fiercely or explode.
  • TetrahydrofuranPeroxide forming ethers can ignite or explode with strong oxidisers.
  • White phosphorusPhosphorus can ignite or explode with oxidisers.
  • Zinc powderStrong oxidisers can form mixtures with these materials that burn fiercely or explode.

Common quantities

Usually held as: solid, 0.1 M.

Tell us the container size and how many you hold. An estimate is enough to start with, and some items cannot be priced until someone has looked at them.

Where it is commonly held

Hazard statements

  • H272 May intensify fire; oxidiser.
  • H301 Toxic if swallowed.
  • H312 Harmful in contact with skin.
  • H314 Causes severe skin burns and eye damage.
  • H317 May cause an allergic skin reaction.
  • H330 Fatal if inhaled.
  • H334 May cause allergy or asthma symptoms or breathing difficulties if inhaled.
  • H340 May cause genetic defects.
  • H350 May cause cancer.
  • H360FD May damage fertility. May damage the unborn child.
  • H372 Causes damage to organs through prolonged or repeated exposure.
  • H410 Very toxic to aquatic life with long lasting effects.
Precautionary statements
  • P203 Obtain, read and follow all safety instructions before use.
  • P210 Keep away from heat, hot surfaces, sparks, open flames and other ignition sources. No smoking.
  • P220 Keep away from clothing and other combustible materials.
  • P233 Keep container tightly closed.
  • P260 Do not breathe dust, fume, gas, mist, vapours or spray.
  • P261 Avoid breathing dust, fume, gas, mist, vapours or spray.
  • P264 Wash hands and exposed skin thoroughly after handling.
  • P270 Do not eat, drink or smoke when using this product.
  • P271 Use only outdoors or in a well-ventilated area.
  • P272 Contaminated work clothing should not be allowed out of the workplace.
  • P273 Avoid release to the environment.
  • P280 Wear protective gloves, protective clothing, eye protection and face protection.
  • P284 In case of inadequate ventilation wear respiratory protection.
  • P301+P316 IF SWALLOWED: Get emergency medical help immediately.
  • P301+P330+P331 IF SWALLOWED: Rinse mouth. Do NOT induce vomiting.
  • P302+P352 IF ON SKIN: Wash with plenty of water.
  • 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.
  • P317 Get medical help.
  • P318 If exposed or concerned, get medical advice.
  • P319 Get medical help if you feel unwell.
  • P320 Specific treatment is urgent (see supplemental first aid instruction on this label).
  • P321 Specific treatment (see supplemental first aid instruction on this label).
  • P330 Rinse mouth.
  • P333+P317 If skin irritation or rash occurs: Get medical help.
  • P342+P316 If experiencing respiratory symptoms: Get emergency medical help immediately.
  • P362+P364 Take off contaminated clothing. And wash it before reuse.
  • P363 Wash contaminated clothing before reuse.
  • P370+P378 In case of fire: Use suitable extinguishing media to extinguish.
  • P391 Collect spillage.
  • P403 Store in a well-ventilated place.
  • P403+P233 Store in a well-ventilated place. Keep container tightly closed.
  • P405 Store locked up.
  • P501 Dispose of contents and container in accordance with local, regional, national and international regulations.

Substance as classified, dilutions may differ.

Questions

Is 0.1 M potassium dichromate weak enough to count as ordinary waste?

No. A 0.1 M solution may be less hazardous than the solid, but it still contains chromium(VI) and the salt is very toxic to aquatic life, so it remains a hazardous waste. List it with its strength. It leaves by specialist collection in the same way as the solid.

Green has appeared in the jar. What does that tell us?

It tells you some chromium(VI) has been reduced to chromium(III), usually because organic matter got in. It says nothing reliable about how much remains. If you know what might have contaminated it, such as a used spatula, say so when you arrange collection, because the contents are no longer pure.

Who should handle the jars when we draw up a list for collection?

A suitably trained and authorised person working under the establishment's chemical safety procedures. The absence of a previous skin or respiratory reaction does not establish that handling is safe. Listing can usually be done with the jars left closed and in place. Raise any past reactions with your occupational health contact.

Guidance only. Check your own risk assessment and your supplier's safety data sheet.

Hazard data source: PubChem GHS Classification, retrieved 31 Oct 2026. Formula Cr2K2O7. EC number 231-906-6.

Request collection Add to register
Search the chemical database