Write an activity to show that water can be made to boil even at a temperate below its normal boiling point (100 °C).
Activity:
i) Take some warm water in a cup. Gently, fill a 12ml plastic syringe with around 3ml of the warm water from the cup.
ii) Hold the syringe horizontally and press your index finger tightly over the tip of the syringe.
iii) Slowly pull out the plunger. The plunger will show some resistance and it pulls back in the opposite direction.
iv) Allow the plunger to slide back slowly into the syringe and then pull the plunger out again. Release the plunger quickly.
v) Pull the plunger out the 2nd time. Bubbles will start forming as the water in the syringe boils.
Explanation: The boiling of water does not only depend on temperature. Pressure also plays a role in the boiling of any liquid. When the pressure goes down below the atmospheric pressure of 1atm, water starts to boil at a temperature lower than its boiling temperature. By pulling the plunger out, we increase the volume inside the syringe but decrease the pressure. This causes the water molecules to gain more kinetic energy. The increase of energy breaks the forces of attraction between the water molecules and they begin to move freely. Hence the water starts to boil.