Water related activities    Salty and fresh    Salt water tester   Sticky water

 These can be a source of fun at the same time as being educational. If you are trying to find a topic with cross-curricular potential, water may well just fit the bill.

Salty and fresh

To demonstrate the relative amounts of salt and fresh water on the planet Earth you can use a 2 litre clear plastic bottle, add 1940 cm³ water with a little green food colouring to represent salt water, and on the top layer, 60 cm³ oil to show the amount of fresh water.

Figure 2 - Relative proportions of salty:fresh water on Earth

Food colouring is water based so will not mix with oil but you may be able to buy coloured oil intended for use in oil burners at home.

Salt water tester

Figure 3 - Salt water tester circuit

Why not construct a tester to see if salt and/or fresh water conduct electricity? If electric circuits are familiar then connect a buzzer into a circuit (Fig. 3) made with two lolly sticks covered with aluminium foil (test probes). Check the buzzer is connected correctly in the circuit with the battery (black wire to black wire and red to red) by touching the two foil sticks together and listening for the buzz. The battery shown is made up of two 1.5 V cells in a battery holder (SSERC Stock No. 835, battery holder only, 20p).

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A light bulb can be used but needs more electricity than a buzzer to function. Hold the probes in the test liquid (salty or fresh water) about 2-3 cm apart. If the test liquid completes the circuit and allows the current to flow, the buzzer will operate. If the buzzer sounds then the test liquid conducts electricity.

Sticky water

A water molecule consists of one oxygen and two hydrogen atoms bonded together. These are arranged in a way that makes them “attractive” to other water molecules. It may seem strange to think of water molecules as being “sticky” but they do have this interesting quality, which can form the basis of simple investigations.

Figure 4 - Water molecules stick together

Surface tension