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. How would you identify the gas evolved, if any, during the reaction?

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.