Incompatible Chemical Mixtures

When Mixing Chemicals Is Dangerous

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Some chemicals release toxic substances when mixed together. Doug Armand/Getty Images

Some chemicals shouldn't be mixed together. In fact, these chemicals shouldn't even be stored near each other on the chance that an accident could occur and the chemicals could react. Be sure to keep incompatibilities in mind when reusing containers to store other chemicals. Here are some examples of mixtures to avoid:

  • Acids with cyanide salts or cyanide solution. Generates highly toxic hydrogen cyanide gas.
  • Acids with sulfide salts or sulfide solutions. Generates highly toxic hydrogen sulfide gas.
  • Acids with bleach. Generates highly toxic chlorine gas. An example of this would be mixing bleach and vinegar.
  • Ammonia with bleach. Releases toxic chloramine vapors.
  • Oxidizing acids (e.g., nitric acid, perchloric acid) with combustible materials (e.g., paper, alcohols, other common solvents). May result in a fire.​
  • Solid oxidizers (e.g., permanganates, iodates, nitrates) with combustible materials (e.g., paper, alcohols, other common solvents). May result in a fire.
  • Hydrides (e.g., sodium hydride) with water. May form flammable hydrogen gas.
  • Phosphides (e.g., sodium phosphide) with water. May form highly toxic phosphine gas.
  • Silver salts with ammonia in the presence of a strong base. May generate an explosively unstable solid.
  • Alkali metals (e.g., sodium, potassium) with water. May form flammable hydrogen gas.
  • Oxidizing agents (e.g., nitric acid) with reducing agents (e.g., hydrazine). May cause fires or explosions.
  • Unsaturated compounds (e.g., substances containing carbonyls or double bonds) in the presence of acids or bases. May polymerize violently.
  • Hydrogen peroxide/acetone mixtures when heated in the presence of an acid. May cause explosions.
  • Hydrogen peroxide/acetic acid mixtures. May explode upon heating.
  • Hydrogen peroxide/sulfuric acid mixtures. May spontaneously detonate.

General Advice About Mixing Chemicals

While it may seem like chemistry is a good science to learn through experimentation, it's never a good idea to randomly mix together chemicals to see what you'll get. Household chemicals aren't any safer than lab chemicals. In particular, you should use care when dealing with cleaners and disinfectants, since these are common products that react with each other to yield nasty results.

It's a good rule of thumb to avoid mixing bleach or peroxide with any other chemical, unless you're following a documented procedure, are wearing protective gear, and are working under a fume hood or outdoors.

Note that many chemical mixtures produce toxic or flammable gases. Even in the home, it's important to have a fire extinguisher handy and work with ventilation. Use caution performing any chemical reaction near an open flame or heat source. In the lab, avoid mixing chemicals near burners. At home, avoid mixing chemicals near burners, heaters, and open flames. This includes pilot lights for ovens, fireplaces, and water heaters.

While it's common to label chemicals and store them separately in a lab, it's also good practice to do this in a home. For example, don't store muriatic acid (hydrochloric acid) with peroxide. Avoid storing household bleach together with peroxide and acetone.