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

Silver chloride (CAS 7783-90-6): storage and disposal

Silver chloride is a white solid kept in school, college and university stores for precipitation and photography demonstrations. Its only classified hazard is that it is very toxic to aquatic life with long lasting effects, which sounds modest but is the reason it counts as a hazardous waste. A tiny amount of white residue is still silver that must not reach a drain.

CAS number
7783-90-6
Form
Solid
Storage class
General
Signal word
Warning
Usual EWC code
16 05 06*
  • Hazardous to the environment pictogramHazardous to the environment

What to do this week

  1. Check the label is readable and write down the opened date if it is not already there.
  2. Check it is stored as general stock and apart from the items listed under "Do not store with".
  3. 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

A clear bottle on an open shelf is the usual mistake. Silver chloride reacts to light, so it belongs in a closed cupboard, in an opaque or dark container, away from windows and bright prep-room lighting. It has no special corrosive or oxidiser needs, so a general shelf is enough, but it should not share a tray with stock that is wet or that drips. Label it clearly, since a white powder or a filtered residue left in a flask after a lesson is easy to confuse with other white solids. Keep a note of when it was made or received, and if it came out of a practical, say so on the label.

How to tell it has deteriorated

Light is the whole story here. Fresh silver chloride is white or very pale, and on exposure to light it turns grey, then violet or purple-grey, as silver is freed at the surface. A bottle on a windowsill will therefore show a coloured crust on the side facing the glass, and a stored precipitate left in a beaker will darken within the room's normal lighting. This is a colour change in a stable solid, not a sign of danger, but it tells you how the stock has been kept. Check labels, caps and any residue that has dried out in a tube or on a filter paper.

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 non-regulated or low hazard laboratory pack with compatible chemicals.

Start with what must not happen to it. Silver chloride must not be washed into a sink, even as a thin cloudy rinse, and it must not go in the bin because the aquatic classification applies to it however little is present. Residues left on filter paper or in flasks after a practical should be identified as silver chloride waste and included in the specialist collection request without rinsing or scraping them out beforehand. The code in a laboratory pack is 16 05 06*, and discarded inorganic stock outside a laboratory pack is 16 05 07*. Request a specialist collection and say where the material came from.

Waste codes and transport details for Silver chloride
EWC code, laboratory chemicals16 05 06*
Discarded inorganic chemical, not a laboratory pack16 05 07*
Hazardous wasteYes

The code depends on where the waste came from and what it is mixed with. Use the waste code finder to see why.

Common quantities we collect

Usually held as: solid.

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

  • H410 Very toxic to aquatic life with long lasting effects.
Precautionary statements
  • P234 Keep only in original packaging.
  • P261 Avoid breathing dust, fume, gas, mist, vapours or spray.
  • P271 Use only outdoors or in a well-ventilated area.
  • P273 Avoid release to the environment.
  • P304+P340 IF INHALED: Remove person to fresh air and keep comfortable for breathing.
  • P319 Get medical help if you feel unwell.
  • P390 Absorb spillage to prevent material damage.
  • P391 Collect spillage.
  • P403+P233 Store in a well-ventilated place. Keep container tightly closed.
  • P405 Store locked up.
  • P406 Store in corrosive resistant container with a resistant inner liner.
  • P501 Dispose of contents and container in accordance with local, regional, national and international regulations.

Substance as classified, dilutions may differ.

Questions

Why has our silver chloride gone grey and purple?

Light has acted on the surface and freed a little silver, which darkens the white solid. It is a normal change for this salt. The material is still waste for collection, so record the colour on the container.

Is it really hazardous waste when the only hazard is aquatic?

Yes. The classification as very toxic to aquatic life with long lasting effects is enough. Even small residues must be collected and must not go to a drain or general waste.

Can precipitate from a lesson be rinsed away?

No, never. Rinsing would send silver down the drain, which must not happen. Collect the solid and its filter paper in a labelled container and include it in the collection request.

How should we store it between lessons?

In a dark or opaque closed container in a cupboard, away from windows. A general shelf is fine because it needs no special corrosive or oxidiser storage, but it must be labelled and dated.

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 AgCl. EC number 232-033-3.

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