3. (a) When calcium metal is added to water, the gas evolved does not catch fire but the same gas evolved on adding potassium metal to water catches fire. Explain why? (CBSE 2014)
The gas evolved when calcium metal is added to water is hydrogen gas (H2). Hydrogen gas itself is not flammable, so it does not catch fire.
On the other hand, when potassium metal is added to water, it reacts vigorously and releases hydrogen gas as well. However, in this case, the hydrogen gas produced can catch fire because potassium is a highly reactive metal. The reaction between potassium and water is more exothermic and produces enough heat to ignite the hydrogen gas, resulting in a fire.
In summary, the difference in reactivity between calcium and potassium metals is the reason why the gas evolved from their reactions with water behaves differently regarding flammability.
In both cases the gas evolved is H2. When calcium reacts with water the heat evolved is not sufficient for hydrogen to catch fire. On the other hand potassium reacts with water violently and lot of heat is evolved which is sufficient for hydrogen to catch fire.
Answers & Comments
Answer:
The gas evolved when calcium metal is added to water is hydrogen gas (H2). Hydrogen gas itself is not flammable, so it does not catch fire.
On the other hand, when potassium metal is added to water, it reacts vigorously and releases hydrogen gas as well. However, in this case, the hydrogen gas produced can catch fire because potassium is a highly reactive metal. The reaction between potassium and water is more exothermic and produces enough heat to ignite the hydrogen gas, resulting in a fire.
In summary, the difference in reactivity between calcium and potassium metals is the reason why the gas evolved from their reactions with water behaves differently regarding flammability.
Hope that helps!
Explanation:
In both cases the gas evolved is H2. When calcium reacts with water the heat evolved is not sufficient for hydrogen to catch fire. On the other hand potassium reacts with water violently and lot of heat is evolved which is sufficient for hydrogen to catch fire.