Conductivity

1. Add some salt to the water and stir it until the salt is dissolves.
2. Place the batteries in the battery holder. 
3. Using a cable with alligator clips, connect the longer leg of the LED to the positive wire of the battery holder.
4. Wrap the lower part of two wooden sticks with aluminium foil. 
5. Connect the remaining contact of the LED spotlight to the aluminium of one of the sticks with a wire with crocodile clips. 
6. Take another wire and connect the negative wire of the battery holder to the aluminium of the second stick. 
7. Insert the sticks into the glass of salt water, on different ends, making sure they don’t touch each other. If your battery holder has a switch, make sure it is in the ON position. The LED bulb should light up. 

THEORY: 

Salts dissolved in water break down into positively and negatively charged ions. Conductivity is defined as the ability of water to conduct an electric current through dissolved ions. The strongest common positive ions are sodium (Na+), calcium (Ca+2), potassium (K+) and magnesium (Mg+2). The strongest common negative ions are chloride (Cl-), sulfate (SO4-2), carbonate, bicarbonate. Nitrates and phosphates do not contribute significantly to conductivity, although they are very important biologically.  

Salinity is a measure of the amount of salts dissolved in water. Salinity and conductivity are related because the amount of dissolved ions increases the values of both. the highest percentage of salts in the sea is sodium chloride (NaCl). However, other saline waters, such as those of the Mono Lake in California (USA), have elevated salinity due to a combination of dissolved ions such as sodium, chloride, carbonate, and sulphate. 
 

Did you know… 

One of the processes to get the salt from the sea to your home is by drying salt water with the sun's energy. The water evaporates, the salt remains.

For several years already, scientists have been doing research on batteries based on sodium (instead of litium), which is a component of sea salt. First versions are in use already, but at the moment, they are still bigger than lithium ion batteries. Nevertheless, there is the hope that they might be able to replace the lithium ion batteries, reducing the use of the this less abundant element.

Evaluation: 

Explain how the electrical circuit works in this experiment.

Reflection Questions:

1. What would happen if you would use tap water instead of salt water for this experiment?
2. What other materials from everyday life work as electrical conductors, as well?

Additional Activities:

Replace the batteries and the battery case by a solar panel. Unlike the battery case, you can’t turn off the solar panel. Nevertheless, you can open or close the electrical circuit by connecting or disconnecting the crocodile clip that connects one of the cables of the solar panel with the other elements of the experiment.

As soon as you connect the last wire, make sure that the sticks don’t touch each other.

For safety reasons, connecting the second cable of the battery case to the electrical circuit should be last step.

In this experiment you can see how a simple electrical circuit works. You have all the necessary elements: The batteries as power source, the LED as consumer, the cables (and the salt water) as connectors. Whenever the circuit is closed, the electrons “flow”, the consumer works. If only one of these connections is broken, the whole system stops.