Materials
• Rectangular tank with a divider
• Bottle containing salt solution
(approximately 75 g salt dissolved
in 1 l water)
• Two beakers containing tap water,
at room temperature
• Food colouring (two different
colours)
• Ice
Procedure
1. Calculate the densities of the tap
water and the salt solution. To do
this, students measure the weight
of a known volume of water, making
sure to subtract the mass of the
container from the total mass of
the container plus liquid. The density
can then be calculated, since
density (r) is mass (m) divided by
volume (v) (or r = m/v).
2. Place the tap water in one
compartment of the tank and salt
solution in the other.
3. Add a few drops of food colouring
to the water in each compartment,
so that each has a different colour.
4. What do you predict will happen
when you remove the divider
between the compartments?
Explain your reasoning.
5. Remove the tank divider. What
happens? Are your observations
consistent with the densities you
measured?
6. Empty the tank and the beakers.
Now fill one beaker with hot tap
water and one beaker with ice-cold
water.
7. Add a few drops of food colouring
to each of the beakers (a different
colour in each beaker).
Activity 1: Investigating water density and stratification
8. Place the hot water in one tank
compartment and the ice-cold
water in the other. What do you
predict will happen when you
remove the divider? Explain your
reasoning.
9. Remove the tank divider. What
happens? Is it as you predicted?
10. After observing the new
equilibrium in the tank, place
your fingertips on top of the fluid
surface and slowly move your
hand towards the bottom of the
tank. Can you feel a temperature
change?
11. How might the effects of climate
change, such as warming and
melting of sea ice, affect the
vertical structure of ocean water?
Discuss possible scenarios.