Question

What happens when potassium is added to water?
(a) No reaction
(b) Metals melts and float
(c) Metal is set on fire
(d) Metal move around quickly on water

Answer 1

Hint: When potassium reacts with water, it forms base, potassium hydroxide whose density is lower than water. It is also a very reactive metal due to only one electron in its outermost shell. It burns with a lilac flame.

Complete step by step solution:
Let us know about in what way and in what potassium reacts with water.
Potassium reacts rapidly and intensely with water, forming a colorless basic potassium hydroxide solution and hydrogen gas, according to the following reaction mechanism:
$\text{2K(s)+2}{{\text{H}}_{2}}\text{O}\to \text{2KOH(aq)+}{{\text{H}}_{2}}(\text{g)}$
This is an exothermic reaction and potassium is heated to such an extent that it burns a purple flame. Additionally, hydrogen released during the reaction strongly reacts with oxygen and ignites. Potassium reacts with water more slowly than does rubidium, which is placed under potassium in the periodic chart. It reacts with water more rapidly than does sodium, which is placed higher in the periodic chart. There is sometimes a small explosion at the end of the reaction.
Therefore, the correct options are
(b) Metals melts and float
(c) Metal is set on fire
(d) Metal move around quickly on water

Note: Potassium is non-water soluble but it does react with water as was explained earlier. Potassium compounds may be water soluble. Examples are potassium dichromate with a water solubility of 115g/L, potassium permanganate with a water solubility of 76g/L, potassium iodide with a water solubility of 92g/L and potassium iodide, of which even up to 1480g may be dissolve in one litre of water.