Observing Convection

Aim: To observe convection in a liquid.

Equipment: 200ml beaker, water, tweezers, a crystal of 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 200ml beaker with 150ml cold water.
3. Place the beaker on top of the tripod and gauze 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 of 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. 

Result: The heat rose up the crystal. 

Discussion: When we added the potassium permanganate to the liquid and turned on the Bunsen burner, the heat from the flame rose it up. That happened because hot water is less dense and hot water rises. The purple crystal helped us see it.