The mystery of Gibraltar |

	The mystery of Gibraltar
What’s the mystery?	Sailors who were passing through the strait of Gibraltar observed a strange fact. They found that water was pouring into the Mediterranean, a land-locked sea which also has many rivers flowing into it; however, the sea level is not going up all the time. How could this be?
Domain(s)	Chemistry
Subdomain keywords	Solutions and their properties.
Age group	12 to 16 years old.
Expected time for the mystery	Approximate time for teacher preparation: 40 min.Approximate time in classroom: two 45-min lessons.
Safety/supervision	No restrictions needed.Disclaimer: the authors of this teaching material will not be held responsible for any injury or damage to persons or properties that might occur in its use.
Preparation and list of materials	A story about the observations of the sailors, salt, food colouring.
Learning objectives	Students learn about the solutions of a particular substance which can have various concentrations and thus various densities. These properties have an impact on the behaviour of the solutions.
Resources	You can see the first experiment here: Water density – cold vs. hot and salt water vs. fresh water For an overview of the ocean currents in the Mediterranean, see this: Ocean current flows around the Mediterranean and Atlantic