My Education Junction

A long time ago we did an experiment I called Let’s Make Rain. Basically, the experiement demonstrates condensation.  When the water vapor cools it begins to fall creating rain.  

By modifying the experiment we can use the same principal to distill water.

What you need:

1-2 liter soda bottle cut in two (see photo for proportions)

1 cup salt water

A small glass that will fit inside of your bottle

What you do:

I began by heating water in microwave for a little less than 2 minutes. Heating the water allows you to create a saturated solution. I then added roughly 3 tbsp of salt to the water and stirred the solution making sure the salt was dissolved. At this point we poured the salt solution in the bottom half of our soda bottle. We then placed our small cup in the center of our solution and then replace the top half of the bottle only this time we do so in an inverted fashion. We then placed the soda bottle out in the sun and checked periodically as condensation formed on the walls and top of the bottle. As the day progressed the temperature dropped, and  water droplets began to fall into the cup placed at the bottom of our soda bottle. The water that has evaporated and then condensed is pure water.  The salt remains at the bottom of the soda bottle. The only problem was that we did not collect a significant amount of water in our cup, and I attribute that to the fact we did not have a bigger drop in temperature.

I had hoped by sitting the bottle in the sun and allowing the process to take place during the course of the day we would watch the process occur as it ordinarily would. If our evening was cooler we might have had more success, but with a little intervention we can still create more dramatic results. If you place ice in the inverted top half of your bottle you will create rapid cooling, hence your solution will condense faster, and you will collect more pure water in the cup. Also, heating the water to a higher temperature helps.

The great thing about this experiment is that children approach it with certain expectations. They expect the water in the glass to taste salty, but they are amazed and surprised when they taste fresh water. The bottle I used in our experiment comes from a science kit. We use pop bottles quite often, but I am not keen on buying pop so I bought this bottle instead. It was created for the purpose of doing experiments.

Give it try.

Filed under: Science on July 7th, 2007