When discovering expired chemicals, the first consideration is **safety and legal compliance**. The following provides step-by-step framework recommendations, but please note: **Non-professionals should not operate without authorization, and be sure to give priority to contacting the local environmental protection department or professional institutions for processing.**. --- ###First step: Confirm the identity of the chemical 1. **Check the label** Check the chemical name, CAS number, and hazard identification (such as corrosive, flammable, highly toxic, etc.) on the container label to record valid information. 2. **Judge potential risks** If the label is blurred, try to guess through the following clues： -**Physical state**(liquid/solid/gas? color? Is there precipitation or crystallization? ） -**Odor** (only for long-distance sniffing in a ventilated environment, avoid direct inhalation) -**Container material**(glass/plastic? Some chemicals need to be kept away from light or in special containers). --- ### Step 2: Assess security risks 1. **Common risks of expired chemicals** -Decomposition produces toxic gases (for example, some organic peroxides may decompose explosively). -Corrosion of the container after moisture absorption and deliquescence (for example, sodium hydroxide may leak after deliquescence). -When the oxidizing agent is mixed with the reducing agent, it causes spontaneous combustion (such as nitrate in contact with organic matter). 2. **Situations where self-operation is prohibited** -Contains highly toxic (such as cyanide), radioactive, or highly reactive (such as sodium metal, concentrated sulfuric acid). -The label is marked as “explosive”, “highly toxic” or contains heavy metals such as mercury and lead. --- ###Step 3: Legal compliance processing 1. **Contact a professional organization** Provide chemical information and recycle it by professionals (you can call the 12369 environmental protection hotline for consultation in China). 2. **Temporary storage recommendations** - Keep the original container sealed and avoid light and high temperature. -Different types of chemicals are stored separately (acids and alkalis, oxidants and reducing agents need to be isolated). --- ###Step 4: Possible reuse directions (only for professionals) If it is confirmed that the chemical is stable and meets the experimental conditions, **Under the premise that protective measures are in place**, some expired chemicals can be tried： 1. **Teaching demonstration experiment** -Copper sulfate (may be partially hydrolyzed after expiration): Recrystalline experiment to observe the growth of blue crystals. -Hydrogen peroxide (decomposition into water and oxygen): Catalytic decomposition experiment (addition of manganese dioxide). 2. **Simple synthesis** -Acetic acid (may be acidified after expiration): reacts with carbonates to produce carbon dioxide (ventilation required). -Ethanol (may contain water): distilled and purified or made into a simple fuel (fire prevention measures are required). --- ### Important reminder -**Personal protection**: You must wear goggles, chemical-proof gloves, and experimental clothing to operate in a fume hood or open space. -**Legal risks**: Some chemicals are controlled (such as ammonium nitrate and potassium permanganate), and it may be illegal to deal with them privately. -**Environmental responsibility**: The waste liquid needs to be neutralized and then treated (such as acid liquid neutralized with sodium bicarbonate), and cannot be dumped directly. **Please always put safety first! ** If safety cannot be ensured, proper handling is more valuable than taking risks.