Name the metals which reacts violently with cold water. Write any three observations you would make when such a metal is dropped into water. How would you identify the gas evolved, if any, during the reaction ?
Sodium and potassium reacts violently with cold water. The three observations which can be seen are:
(i) Metal melts.
(ii) Hydrogen ignites instantly.
(iii) It fizzies rapidly.
When potassium and sodium dropped in water, hydrogen gas is formed and it is recognized easily because hydrogen gas immediately catches fire with pop sound.
The reactions are:
2Na(s) + 2HaO(l) → 2NaOH + H2(g)
2K(s) + 2HaO(l) → 2KOH(aq) + H2(g)