What Is the Difference Between Sodium Cyanide & Potassium Cyanide?

Potassium cyanide and sodium cyanide are outwardly very similar. They are both white powders that, when they react with air or water, release deadly hydrogen cyanide gas. The gas has a distinctive smell, resembling bitter almonds, but this smell is not noticeable to everyone. Inhaling the gas released by either potassium cyanide or sodium cyanide leads to death within minutes. The two substances have slight differences in their reactivity and chemical properties.

Reactivity

• Both potassium and sodium cyanide react with water and CO2 to produce hydrogen cyanide gas. Sodium cyanide is somewhat more reactive; contact with nitrates, peroxides, chlorates, and nitric acid can cause explosions. Potassium cyanide will also explode in contact with nitrogen chloride and some nitrates. Sodium cyanide is also more dangerous to handle, since the amount of CO2 in the air is enough to react with it to release hydrogen cyanide gas.

Melting and Boiling Points

• Sodium and potassium cyanide have different temperatures at which they turn from solid to liquid (melting) and liquid to gas (boiling), with sodium cyanide doing both at lower temperatures. Potassium cyanide melts at 1173 degrees and boils at 2957 degrees, while sodium cyanide melts at 1045 degrees and boils at 2725 degrees.

Density and Molecular Mass

• Density describes the weight of a given volume of a substance. Sodium cyanide is more dense at 1.6 grams per milliliter as compared to 1.52 grams per milliliter for potassium cyanide. Their molecular masses--expressed on a scale where a single carbon atom has a mass of exactly 12--are also different, with sodium cyanide having a molecular mass of 49.01 and potassium cyanide a mass of 65.12.

Trade Names

• Potassium cyanide is also known as potassium salt. Sodium cyanide has more trade names, being known as Cyanasalt H and S, Cyanobrik, Cyanogran, Cymag, sodium salt or prussiate of soda. Hydrocyanic acid is an umbrella term applied to both potassium and sodium cyanide.