We conducted a science experiment last week – it involved using a variety of liquids to make a “lava lamp”.
We poured some water into a plastic cup, then added some cooking oil. The cooking oil rose to the top of the water and stayed there.
Next we added some drops of food colouring and watched as the droplet slowly made its way down through the oil and into the water where it dissolved.
Then we sprinkled some salt over the oil and watched what happened. The salt sank to the bottom of the cup and then slowly, slowly big bubbles formed and made their way to the top of the cup.
What we think happened: we think the salt sank to the bottom because it was heavier than the oil and the water; as it sank the salt pushed oil down to the bottom of the water. The salt dissolved in the water and the oil floated to the top of the cup in big bubbles.