You may have noticed that when water boils, you can seebubbles that rise to the surface of the water. What is inside these bubbles? Explain.
a. air
b. hydrogen and oxygen gas
c. oxygen gas
d. water vapor
e. carbon dioxide gas
Interpretation:The true optionfor the molecules which are present inside the boiling water bubbles is to be predicted.
Concept Introduction: Any liquid when heated, vaporizes at the temperaturestated as its boiling point and the process is referred as boiling. There occurs formation of bubbles when substances particularly liquids undergo boiling. The phase corresponding to the liquid also changes to vapor during boiling process.
Correct answer: Option (d) that is water vapor.
Reason for true statements: Option (d) the bubbles consists of water vapor.
When water boils, bubble formation occurs. On prolonged heating, the water molecules transform from liquid to gaseous state by gaining sufficient energy through heat. This is the boiling state of water where the boiling water bubble are composed of water vapor.
The reason is that on heating water, its bottom part directly interacts with the water source. This is the hottest surface and here the temperature can rise above water’s boiling temperature. In this way some liquid water gets converted to water vapor thus forming an expanded bubble made of water vapor.
Reason for false statements: Options (a), (b), (c) and (e) are false statements.
Bubbles formed at the initial stage of water boiling are air bubbles which form by the dissolved gases in the solution particularly oxygen as well as carbon dioxide.
Thus, boiling water bubbles comprises of water vapor.