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Chemical incompatibilities
Incompatible chemicals give an undesired chemical reaction when mixed. This usually refers to substances that will react to cause an imminent threat to health and safety through an explosion, fire, and/or formation of toxic materials.
Even everyday chemicals have incompatibilities. For example, did you ever notice that containers of bleach have a warning not to mix bleach and ammonia? When mixed, these substances generate the toxic gases chloramine (NH2Cl) and hydrazine (N2H4), which could cause serious injuries or death.
Other examples of incompatibilities include the reaction of alkali metals such as sodium or potassium metal with water. In this case, the products are extremely basic sodium or potassium hydroxide (corrosive), hydrogen gas (explosive) and a lot of heat (an exothermic reaction). The heat generated is so great that the hydrogen generated will usually ignite.
- It is therefore crucial to get as much information as possible before storing chemical products, initiating a chemical reaction or generating chemical waste. The MSDS is the initial source where to get such information.
- Some chemicals that react dangerously when mixed (non-exhaustive list):
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INCOMPATIBLE PRODUCTS
|
REACTION
|
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Acids with cyanide salts or cyanide solution |
Generates highly toxic hydrogen sulfide gas. |
|
Acids with sulfide salts or sulfide solutions |
Generates highly toxic hydrogen sulfide gas |
|
Acids with bleach |
Generates highly toxic chlorine gas |
|
Ammonia with bleach |
Releases toxic chloramine vapors |
|
Oxidizing acids (e.g., nitric acid, perchloric acid) with combustible materials (e.g., paper, alchohols, other common solvents). |
May result in fire |
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Solid oxidizers (e.g., permanganates, iodates, nitrates) with combustible materials (e.g., paper, alchohols, other common solvents). |
May result in fire |
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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 |
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Silver salts with ammonia in the presence of a strong base |
May generate an explosively unstable solid. |
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Alkali metals (e.g., sodium, potassium) with water |
May form flammable hydrogen gas. |
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Oxidizing agents (e.g., nitric acid) with reducing agents (e.g., hydrazine) |
May cause fires or explosions. |
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Unsaturated compounds (e.g., substances containing carbonyls or double bonds) in the presence of acids or bases |
May polymerize violently |
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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 |
- Potentially explosive combinations of common reagents:
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Acetone |
+ |
Chloroform in the presence of a base |
|
Acetylene |
+ |
Copper silver, mercury or their salts |
|
Ammonia (including aqueous solutions) |
+ |
Cl2, Br2 or I2 |
|
Carbon disulfide |
+ |
Sodium azide |
|
Chlorine |
+ |
An alcohol |
|
Chloroform or carbon tetrachloride |
+ |
Powdered Al or Mg |
|
Decolorizing carbon |
+ |
An oxidizing agent |
|
Diethyl ether |
+ |
Chlorine (including a chlorine atmosphere |
|
Dimethyl sulfoxide |
+ |
CrO3 |
|
Ethanol |
+ |
Silver nitrate |
|
Nitric acid |
+ |
Acetic anhydride or acetic acid |
|
Picric acid |
+ |
Heavy metal salt such as Pb, Hg, or Ag silver oxide + Ammonia + ethanol |
|
Sodium |
+ |
A chlorinated hydrocarbon |
|
Sodium hypochlorite (bleach) |
+ |
An amine |
