Question

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

1. Name two metals which react violently with cold water. List any three observations which a student notes when these metal are dropped in a beaker containing water.
2. Write a test to identify the gas evolved (if any) during the reaction of these metals with water.

Answer 1

Sodium and potassium are two metals that react violently with cold water.

Three observations when such a metal is dropped in water are:

1. Reaction is highly exothermic, i.e., a huge amount of heat is produced.
2. Hydrogen gas is evolved in the reaction.
3. A small explosion takes place because the heat produced in the reaction burns the hydrogen gas. Hydrogen can be identified by the ‘pop’ sound it makes while burning.

Answer 2

a. Sodium and potassium are two metals that react violently with cold water.

Three observations when such a metal is dropped in water are:

1. Effervescence: Strong bubbling brought on by the gas's quick release.
2. Heat Evolution: The exothermic reaction warms the water and occasionally melts the metal into a ball.
3. Flame Formation/Pop Sound: When the hydrogen gas ignites, a distinctive pop sound or a yellow (for sodium) or lilac (for potassium) flame may occasionally be seen.

b. Test for the Evolved Gas: The gas evolved during the reaction is hydrogen (H₂). To confirm its presence, bring a burning matchstick or a glowing splint near the mouth of the beaker. If the gas burns with a ‘pop’ sound, it confirms the presence of hydrogen.