Particle Theory of Matter - Convection 2

                                                                          Convection

When particles are heated the distance between the particles increases. This means that objects will expand. When liquid or gases expand they become less dense. A gas or liquid which is less dense will rise through a more dense gas or liquid. This is the explanation for the well-known tendency of hot fluids to rise and cold fluid to sink. Scientist call this process convection.

Observing Convection I

Aim:  To observe convection in a liquid

Equipment:  200 mL beaker, water, tweezers, a crystal potassium permanganate, a drinking straw, Bunsen burner, heat mat, tripod and gauze mat

Method:

1. Set up a Bunsen burner on a heatproof mat. Put the gauze mat on the tripod but leave it just to one side of the Bunsen burner

2. Fill a 200 mL beaker with 150 mL cold water

3. Place the beaker on top of the tripod and gauze mat and allow it to settle for a few minutes

4. Carefully insert a drinking straw down one side of the beaker, ensuring the straw is touching the bottom of the beaker. Be careful as you do not want to disturb the water too much

5. Using tweezers, drop a crystal potassium permanganate down the inside of the straw. Wait for the crystal to settle on the bottom of the beaker

6. Very gently, so to not disturb the water, remove the straw

7. Light the Bunsen and slide it under the tripod so that you are only heating the outside of the beaker where the crystal is.

Observations:  The purple colour from the permanganate rises vertically,then travel horizontally across the surface of the water. Small circular currents can be seen transferring the purple colour through the beaker.

Explanation:  When the water in the very bottom, the space between the water particles increases. This means this region of water becomes less dense and rises. Denser colder water flows in to replace the rising water.