Try this fun experiment to observe some differences between salt and freshwater. Our salty seas are different to our freshwater lochs, rivers and ponds – and the answer is because of salt!
Essentially, water gradually makes its way to the sea from rivers, but along the way salts dissolve in this water from the Earth. So, it is salty when it reaches the ocean. Water also then evaporates out of the ocean, leaving the salts behind. This freshwater then falls over the land (e.g. rain) and the cycle starts again.
Many animals that have adapted to saltwater habitats could not survive in our freshwater (and vice versa). Seabirds can drink saltwater (which is very unpleasant for us humans!) and they excrete the excess salt through salt glands above their eyes. Many fish species eliminate salt through their gills, and turtles cry salty tears!
Why do fish swim in saltwater? … because pepper makes them sneeze!
What you will need:
- Two clear glasses
- Water
- Salt
- Two eggs
How to play:
- Start by introducing the topic to your group – have you ever splashed around in the sea? You might have noticed the water is salty! Do you think it’s easier to float in freshwater or saltwater?
- Fill two glasses with water – about ¾ full. Add a cup of salt to one glass and sir.
- Ask your group if they think an egg will sink or swim in freshwater? After some guesses, add the first egg to the cup with no salt (freshwater).
- What about saltwater? After some guesses, add the second egg to your saltwater glass.
- Did you notice a difference? With enough salt, your egg will float in the saltwater cup (you can add some more salt if needed!)
- Here’s how it works: very heavy things will sink in both, and very light things will float in both. However, saltwater is heavier than freshwater. So, if you add something that is in between that weight (i.e. lighter than saltwater but heavier than freshwater) it will float! You could use the Dead Sea as an example here.
- Your group can check if other things sink or swim. Some suggestions include soap, pegs, grapes and bouncy balls
- Make sure to wash hands after handling eggs.