Exploring Potassium Metal: Physical, Chemistry Properties, Manufacture

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Physical properties of Potassium Metal

PropertyValue or Description
Element SymbolK
Atomic Number19
Element ClassificationAlkali Metal
Melting Point63.7°C
Boiling Point759°C
Density0.862 g/cm³
AppearanceSilver-white, soft, and malleable
CutabilityEasily cut with a knife
OxidationForms 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)

Frequently Asked Questions

How is Potassium Manufactured?

People electrolyze molten sodium chloride to produce metal sodium. You might think that metal potassium is also produced through the similar way, but that would be incorrect. Potassium is displaced from molten potassium chloride by metal sodium in factory.

Na(l) + KCl(l) → K(g) + NaCl(l)

You might find this strange. Generally, a more reactive metal displaces a less reactive one. Although potassium is more reactive than sodium, its phase change compensates for this difference. The entropy increases significantly when the liquid reactants transform into gaseous products. Decreased Gibbs free energy makes the reaction spontaneous. Additional measures encourage chemical equilibrium to move to right. The temperature is maintained around 850°C during this exothermic reaction. The potassium gas is also removed from the products.

Why is Electrolyzing Molten Potassium Chloride Infeasible for Producing Potassium Metal?

The 7.6% potassium will dissolve in molten potassium chloride at 800°C. It reacts with chlorine to reforme potassium chloride at the cathode, leading to low production efficiency.

Where is Potassium Found on Earth?

Potassium is the seventh most abundant element in the Earth's crust. It makes up 2.6% of the Earth's crust. Due to its high reactivity, potassium loses an electron and form compounds with other anions easily, so free potassium does not exist in nature. Potassium is mainly found in minerals. Soil and dried-up salt lakes are also rich in potassium.

Anec  > Chemistry > Alkali metal