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Student Activity - Saline currents
Activity idea
When you add salt to a glass of water and stir the water the salt disappears. We all know the salt has not just vanished, if you taste it you know it is still there. Have you ever thought whether the salt in the water has any effect on the water? Freshwater that has been collected on land flows back into the oceans of our world. Do the freshwater and salt water just mix, and if so would this happen in any particular way? Let’s investigate….
Instructions
You will need
- four translucent (see-through) bottles of equal size with lids - recommended 1.5 litre plastic bottles
- piece of thin cardboard, preferably waxy
- blue food dye
- water - enough to full four bottles
- salt
- marker pen
- two trays or a workbench set up that allows accidental water spillage.
Method
- On two of the bottles write ‘fresh’ and on the other two bottles write ’salt’.
- Fill all four bottles with water.
- Add a few tablespoons of salt to both of the ‘salt’ bottles.
- Into ONE of the ‘fresh’ bottles add a few drops of food colouring, enough to turn the water obviously blue.
- Into ONE of the ‘salt’ bottles add a few drops of blue food colouring, enough to turn the water obviously blue.
- Put the lids on all bottles and shake them, making sure the dye is evenly mixed and the salt is dissolved.
- Remove the lids.
- Set up the bottles as shown in the figure, making sure that the blue dyed bottles are on the bottom. Please make sure you do this experiment on a water proof surface that accommodates for any unplanned water spillage.
- Press the waxy cardboard on top of the water bottle without the dye before inverting it.
- To invert the top bottles without spilling them, try placing the cardboard over the top of the bottle, lining them up and then carefully removing the card.
- What do you think is going to happen? Take a note of your predictions and try to be as specific as possible.
- Observe what happens once the card has been removed.
- Check whether your predictions were correct.
- Try the same experiment with the other bottle set up.
- Think and talk about your observations. What factors were the same in the two experiments and what was different? Was your predication correct?
