This experiment is for advanced students. This is a repeat of the experiment: Can Fish Drown? but now we’re going to do this experiment again with your new chemistry glassware.

The aquarium looked normal in every way, except for the fish. They were breathing very fast and sinking head first to the bottom of the tank. They would sink a few inches, then jerk into proper movement again.

The student had to figure out what was wrong. He had set up the aquarium as an ongoing science project, and it was his responsibility to maintain the fish tank. His grade depended on it.

He went to his mom for help. She looked over the setup. “Have you tested the water?”

A quizzical look on his face, the boy said, “Everything is normal nitrates, nitrites, hardness, alkalinity, and pH. The pH was a little acidic, but not outside the proper range.”

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His mother said to him, “Show me how you would look if you were gasping for air and look in the mirror while you do it.”

He did, and he remarked, “I look like my fish.” I swear a light bulb actually appeared over his head and lit all up. He said, “They need air!” His mom was standing near the aquarium holding an air pump, vinyl tubing, and an air stone.

“Looking for this?” His mom said. He and his mom set up the air pump and soon his fish were jumping in the air and kissing him on the cheek. Well, maybe not that last part, but you get the idea. Water does not contain an inexhaustible amount of oxygen in it. It must be replenished if there is something in the water that is using it up.

The oxygen carrying capacity of water varies with conditions. Rainbow trout are found in cold water streams because the colder the water, the more oxygen it will hold. Rainbow trout need lots of oxygen in their water to survive. Other species of fish are found only in warmer water because they are adapted to a condition of less oxygen in the water. Still other fish can gulp the air from the surface if the water is severely depleted of oxygen. I have seen carp gulping air as they swim around in a pond looking for food on a hot summer day.

In this experiment we will discover that water does contain oxygen. We will subject the water to heat and we will see the oxygen for ourselves.

Materials:

• Test tube rack
• Test tube
• Test tube holder
• Rubber stopper
• 90 degree bent glass tubing
• Alcohol burner
• Striker

Be careful not to let your water boil. Pressure will build up inside the test tube because only a small amount of pressure at a time can leave via the glass tubing. Pressure will build up and the stopper will fly off or the test tube will rupture. (Glass shrapnel and boiling water will get all over you. Not a pleasant thought.)

Inserting the glass tubing into and through the stopper is the most dangerous part of this lab or any other lab requiring this to be done. Most lab injuries, student or chemist, are due to cuts from broken glass. Proper technique will save you the pain of a deep cut. Lubricate the rubber stopper with glycerol if you have it. (It is a non-reactive laboratory grease that will not contaminate as badly as household or automotive oils and greases.) DO NOT use any other grease or oil. You probably don’t have any glycerol, so your second choice is just plain old water.

So, water on the tubing, gently start the glass tubing into the stopper. Don’t grip the glass with your hands, get a thick wash cloth, small towel, or work gloves and grab the tubing. Gently twist the tubing as you push gently on the tubing. Don’t pull to one side or the other, make your push a straight line. Once the tubing gets going, don’t stop unless you have to. Your second shot may be much more difficult because you have pushed a lot of the water off the tubing.

You are not going to see a chemical change. You are not going to work with chemicals. You are going to see for yourself that there is oxygen in water. That is, of course, what fish use up in the water. Unless it is replenished, fish can’t breath and they suffocate….not drown. The oxygen is replenished in the wild through various means. We can replenish the water with air pumps and water changes.

C3000: Experiment

Cleanup: Clean everything thoroughly after you are finished with the lab. After cleaning with soap and water, rinse thoroughly. Chemists use the rule of “three” in cleaning glassware and tools. After washing, chemists rinse out all visible soap and then rinse three times more.

Heated surfaces will be hot for awhile. Let things rest for a couple of minutes before doing your cleanup.

Your test tube probably has a blackened surface. It should wipe off easily, or will with a little soap, water, and a light touch.

Storage: Place all chemicals, cleaned tools, and glassware in their respective storage places.

Disposal: Dispose of all solid waste in the garbage. Liquids can be washed down the drain with running water. Let the water run awhile to ensure that they have been diluted and sent downstream.

The filter pump in your fish tank ‘aerates’ the water. The simple act of letting water dribble like a waterfall is usually enough to mix air back in. Which is why flowing rivers and streams are popular with fish – all that fresh air getting mixed in must feel good! The constant movement of the river replaces any air lost and the fish stay happy (and breathing). Does it make sense that fish can’t live in stagnant or boiled water?

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