Question

Name two metals which react violently with cold water. Write any observation you would make when such a metal is dropped into water.

Answer 1

Hint: We have to know that when metal reacts with water, the products formed are metal hydroxide, and water. Alkali metals generally displace hydrogen gas from water. As they displace hydrogen from water, they create a basic solution. Metals that are less active react with boiling water. Non-metals do not react with water. Certain metals react with steam to form oxides of metal and hydrogen.

Complete step by step answer:
We have to know that one of the common features of many alkali metals is that they have the ability to displace hydrogen gas from water. In this process, group 1 metal is oxidized to its metal ion and hydrogen gas and hydroxide ions are formed by reduction of water. The production of hydroxide ions creates an alkaline (or) basic environment.
Alkali metals react violently with water. During an exothermic reaction, enough heat is released off to ignite hydrogen gas.
Metals such as sodium and potassium react violently with cold water.
Some of the observations that can be made are:
1.Metal starts moving over the surface of the water producing a hissing sound.
2.Metal reacts with water leading to small explosions.
3.The metal catches fire and begins to burn.
Potassium reacts with water to form potassium hydroxide with evolution of hydrogen. A high amount of energy is given off. The reaction of potassium with water is written as,
$2K + 2{H_2}O \to 2KOH + {H_2}$
Sodium reacts with water to form sodium hydroxide as products with liberation of hydrogen. A high amount of energy is given off. The reaction of sodium with water is written as,
$2Na + 2{H_2}O \to 2NaOH + {H_2}$
The evolution of gas during the reaction could be recognized by bringing a candle nearby. The candle burns with pop sound representing the evolution of hydrogen gas.

Note:
We have to remember that the reaction of metal with water produces hydrogen gas during the reaction of these two with water that rapidly catches fire. The reactions with water are highly violent and exothermic. Alkaline earth metals also react with water to form hydroxides. The presence of hydroxide ions also creates a basic solution.