Physical properties of Potassium Metal
| Property | Value or Description |
|---|---|
| Element Symbol | K |
| Atomic Number | 19 |
| Element Classification | Alkali Metal |
| Melting Point | 63.7°C |
| Boiling Point | 759°C |
| Density | 0.862 g/cm³ |
| Appearance | Silver-white, soft, and malleable |
| Cutability | Easily cut with a knife |
| Oxidation | Forms potassium peroxide (K₂O₂) and turns yellow when exposed to air due to rapid oxidation |
Chemical properties of Potassium Metal
Potassium has 19 electrons. It prone to react with other substances, because its outermost shell contains only one electron that can be stolen by other elements easily. Hence the pure potassium doesn't exist in natural world. Potassium and sodium share some chemical properties due to similar electron structure. Although it also reacts with oxygen, chlorine, water and alcohols, there are still some differences since the bigger atomic radius makes it more reactive.
Reaction in Oxygen
The interaction of oxygen with potassium at normal temperature and pressure produces oxide (K₂O) and peroxide (K₂O₂).
4K(s) + O₂(g) → 2K₂O(s)
2K(s) + O₂(g) → K₂O₂(s)
When potassium burns in abundant oxygen, it produces a purple flame. The flame is actually yellow, as it is always accompanied by sodium. Therefore, blue glass will filter the yellow light so that the purple flame is visible. The products are potassium peroxide (K₂O₂) and superoxide (KO₂) after combustion.
2K(s) + O₂(g) → K₂O₂(s)
K(s) + O₂(g) → KO₂(s)
Reaction between Potassium and Water
Similar to sodium, potassium will float on a beaker with water and phenolphthalein. It quickly undergoes reactions that release hydrogen gas more vigorously. The excessive heat from reaction ignites hydrogen gas and potassium to emit a bluish-purple light overlaid partially with a yellow light because of sodium impurities. The final product, hydroxide or caustic potash, gives phenolphthalein solution a pink color.
2K(s) + 2H₂O(l) → 2KOH(aq) + H₂(g)