This weekend let’s try some experiments with water.
1. pH of the Planet
If you are thinking big, why not participate in the International Year of Chemistry’s Water–A Chemical Solution: A Global Experiment? The organizers are inviting students from around the world to check the pH of local water sources and then report them. Take a look at the website for details. If you want to check out the experiment, look at the .pdf file in the right sidebar labeled Worksheet- PH of Planet, which gives details about the methods.
2. Water Temperature and Density
- 3 plastic cups
- 4 zipper top plastic bags
- sharpie pen to label the bags
- large container to hold water, or sink or bathtub
- warm water – about bathtub temperature
- cold water
- ice cubes
- Digital water thermometer (optional)
A. Density and Floating – Do bags filled with warm water versus cold water float the same?
Fill your large container with room temperature water. Place a few ice cubes and some cold water in a zipper top plastic bag. Close the top and let the ice cubes mostly melt, so you have very cold water. Label the bag cold. Fill another zipper top plastic bag with warm water and label it warm. Now place the two bags in the large container. What happens? Do both bags float? Does one bag sink? Why or why not?
B. Playing with Temperature – Does pouring water change its temperature?
Label the plastic cups 1, 2 and 3. Pour some of warm water into the plastic cup labeled 1 (say about 1/2 cup or so) and the same amount into cup 2. Take the temperature of the water in both cups, if you have a digital thermometer. The temperature should be the same in both cups. If it is not, dump the cups and refill with warm water again. Once they are the same, place cup 2 aside to serve as the control.
Now quickly pour the water from cup 1 into cup 3. Pour it back and forth from on cup to the other for about two minutes. End up with all the water back in cup 1. Now take the temperature of the water in cup 1 and cup 2 again. Are the two temperatures still the same? Why or why not?
C. Does air change density with temperature?
If you still have warm water and cold water in separate containers, try this activity with air. Fill the remaining two zipper lock plastic bags with roughly the same amount of air, but it shouldn’t be completely filled. You can blow in the air and then quickly seal it up. Now place one bag in warm water (at least bathtub temperature) and the other in cold water. What happens?
(If you got the right amount of air in, the bag in the warm water should expand noticeably).
If you do these experiments, let me know what you find out. And it have a digital water thermometer, think up some more activities with water. I’d love to hear what you come up with.
Digital thermometers for aquariums are relatively inexpensive.