Science Buddies: "Ask an Expert"

why does the water level in the test tube rise as the steel wool oxidizes?The title of my project is "From Gas to Rust:Measuring the Oxygen Content of Air".

Hi,

I can't tell what is happening here. Can you tell me how you oxidized the steel and describe your experimental set up? It sounds like a gas is being produced in the oxidation reaction, so if you can describe your experiment, we can explain the chemistry. Please let me know what grade you are in and whether or not you've had chemistry.

Donna Hardy

I put steel wool inside three of the test tube and three without the steel wool and put it upside down on the test tubeholder so only the mouth of the tube is in the jar of water.Im trying to find out how much the water rises as the steel wool oxidizes, and how much the water rises for the tubes without the steel wool.Im in the 8th grade. Im asking you because my experiment does not seem to work like I planned,nothing is happening.

Hi,

Don't worry, this is still a good project. Figuring out what is going wrong is a big part of doing science. So is trying to get a system that works well so that the experiment can be repeated. When doing an experiment it is always a good idea to repeat it a few times to get an average result. Even if you don't have time to do the repeats for the science fair, its good to say that you would do that if you had the time so that you could confirm your observations.

I think how the experiment is supposed to work is that the oxygen in the tube is used in the oxidation process as the wool rusts. The steel wool is part iron. The oxygen is being combined with the iron in the wool to form iron oxide, or rust. As the oxygen is combined into the rust, the amount of oxygen left in the tube decreases and the water gets sucked up to replace it.

So what could be going wrong? I can think of at least two possibilities. Maybe you can come up with some others too since you know what your apparatus looks like.

1. Is there any rust? if there is no rust yet, no oxygen will have been used and so the water level will not have moved.

2. Maybe oxygen is getting in some other way. Does the water come far enough to seal off any air from getting to the wool another way?

best of luck,
Caroline

Hi,

Caroline has given you some good advice. Now, that I understand the experiment, I have just one additional comment. With your experimental set-up, I would think that the steel would have rusted (oxidized) within a few days and consumed the oxygen in the tube. It sounds like it might be acting like stainless steel wool. You could try expediting the oxidation by adding some vinegar or salt (sodium chloride) if you have time to try this.

Caroline is also right about your project. It's still a very good project. You do have results; you just don't have the results you expect. You do have some work to do to explain your results.

Good luck!

Donna Hardy

I would like to take the time to say thanks and I appreciate all you've done to help me.