Multimeter experiments with electricity and water

Description:

See how the electrical conductivity of water changes depending on what is dissolved in it.

Equipment Needed:

A multimeter, either a digital multimeter or an analog multimeter.

Two or three identical containers for water, like drinking glasses or transparent jars

Distilled water. Grocery stores sell bottled distilled water, usually near their bottled drinking water. “Distilled” means it is high-purity water with nothing dissolved in it

Tap water

Baking soda

Sugar

Table salt

A measuring spoon

The Digital Bits Science Lab Experiment:

First, fill one container with distilled water, and set your multimeter to the “ohms” setting for measuring electrical resistance. Touch the multimeter probes together to check that the zero setting is correct. Then, stick the tips of your probes into the water so that the metal part is completely underwater, holding them an inch or so apart. The electrical resistance should be very high.

Next, put some baking soda in the water – about a teaspoon in an 8-ounce glass. Stir it up until the baking soda dissolves, and measure the electrical resistance again. The resistance should be much lower.

Now, fill a series of glasses, with the following

Tap water
Distilled water + 1 teaspoon sugar
Distilled water + 1 teaspoon salt

…and measure the electrical resistance of each. How are they different?

What is going on here?

You should notice that water by itself is not very conductive; that some things (baking soda and salt) make the solution a lot more conductive; while other things (like sugar) do not. What is happening is this: Really pure water is actually an insulator, and does not conduct electricity very well, so it has a high resistance. But, a lot of things that dissolve in water “dissociate”, that is, they break up into electrically charged parts (ions) that can move around. When the ions move, they conduct electricity. Substances that dissolve in water and form ions like this are referred to as “electrolytes”, because they make it possible for water to conduct electricity.

Not all things that dissolve in water are electrolytes, though – the sugar will not make the water very conductive, because sugar dissolves without breaking up into ions. If your sugar did increase the conductivity a bit, it was probably because it had small amounts of some impurities that were electrolytes.

The tap water should have been more conductive than the distilled water, but not as conductive as the water with salt or baking soda dissolved in it. This is because the water out of your tap is not pure, it has minerals like calcium carbonate dissolved in it. Depending on where you live, you could have “hard” water (which has a lot of dissolved minerals in it and is quite conductive), or “soft” water (which has very little dissolved minerals, and can be almost as non-conductive as distilled water).

You can check the conductivities of other liquids, too, like cooking oil, vinegar, or soda pop. Also, see how adding just a little bit of baking soda or salt to water changes the conductivity, compared to adding a large amount.

Other articles related to this topic:

• Multimeter experiments and introduction
• A classic, easy chemical reaction with baking soda and vinegar
• 1 cup and 1 cup does not make two cups – Experiment with solutions
• How to make copper metal from dissolved copper compounds
• Why is it easier to swim in the ocean? Learn about buoyancy.