Question

Potassium metal reacts with water to give potassium hydroxide and hydrogen gas. Write a balanced chemical equation for this reaction.

Answer 1

Hint: Reaction is exothermic, that is energy is released during the reaction, also the resultant solution from the reaction is highly alkaline because of the presence of hydroxide ion, coming from the strong base Potassium hydroxide.

Complete step by step answer: Potassium metal reacts very rapidly with water to form a colorless solution of potassium hydroxide (KOH) and hydrogen gas ( ${{H}_{2}}$).Hydrogen evolved during the reaction ignites rapidly. The resulting solution is basic because of the dissolved hydroxide. The reaction is exothermic. Early in the reaction, the potassium metal becomes so hot that it catches fire and burns with a characteristic plate lilac colour. The reaction is slower than that of rubidium (immediately below potassium in the periodic table), but faster than that of sodium (immediately above potassium in the periodic table).The balance reaction is given as follows-
\[2K(s)+2{{H}_{2}}O\to 2KOH(aq)+{{H}_{2}}(g)\]
All the alkali metals react vigorously with cold water. In each reaction, hydrogen gas is given off and the metal hydroxide is produced. The speed and violence of the reaction increases as you go down the group. This shows that the reactivity of the alkali metals increases as you go down Group 1.

Note: Potassium hydroxide (KOH) is an inorganic compound and is commonly known as caustic potash. It is a strong base. Potassium hydroxide is usually translucent pellets which becomes tacky on contact with air, because KOH is hygroscopic.