Answer to Question #95441 in General Chemistry for Egbz

Question

A student is investigating the boiling and freezing point of a liquid , He observes the liquid in the apparatus while he gently heats the flask with a Bunsen burner flame. The liquid and its vapour are colourless and transparent. 1. Suggest one observation that will tell the student when the reading on the thermometer show the boiling point of the liquid. 2. Explain why the temperature does not rise above its boiling point even though the flask is still being heated. Use the word thermal energy in your answer . 3. What effect on the boiling point is produce by : a soluble non-volatile impurity, such as table salt and an insoluble foreign substance, such as sand?

Answer 1

1) Upon reaching the boiling point, the liquid starts to actively boil, forming bubbles of vapour, which can be easily observed

2) Further increase of the temperature would be halted by the transfer of thermal energy to the vapour due to the heat of vaporisation. Therefore, as long as the atmospheric pressure in the flask remain constant (meaning its an open system), the temperature will remain constant.

3) Addition of the soluble impurity would increase boiling point, where an insoluble impurity would have no effect on this