Science Buddies: "Ask an Expert"

Hello there Science Buddies. I am a Grade 11 chemistry student, and we are currently working on our science fair projects in class. We started yesterday, and I have used a variation of one of your projects, called "Rusting Out: How Acids Affect the Rate of Reaction." You suggested on your website using simple acids such as lemon juice, orange juice and coffee in order to measure how steel wool rusts in acids of varying pH, and instead I am using HCl acid. I did a test run of the experiment yesterday with steel wool in HCl, and unfortunately there was absolutely no reaction whatsoever, and I am not sure why. I cut the steel wool into a 1 inch piece, inserted it onto a probe thermometer and placed it into a test tube filled with HCl acid just as it was suggested, and there wasn't any reaction taking place at all. Initially, I wondered if there was too much heat being released, and so I even wrapped it with a towel and used a test tube stopper as you suggested, yet I was not able to gather any data, and no reaction was taking place. I also tried lemon juice and orange juice, and the temperature still remained the same at room temperature, with no reactions taking place. I am a bit confused as to what I am doing wrong, so could I please get some assistance? Thank you so much, I greatly appreciate it!

This is the link to the project on your website:

https://www.sciencebuddies.org/science- ... p079.shtml

Hello jonnydepp45

I think, perhaps, you might be going at this too aggressively.

What concentration of HCl are you using? How does it's pH compare to that of the acids suggested in the experiment?

I suspect what is happening is you may be using such a strong concentration of HCl that most of the reaction is taking place while you soak the steel wool in the bowl for 30 seconds. I have assumed here that you are following the experimental procedure to this level of detail.

If that is the case, most of the reaction will have happened while the sample is in the bowl, with little, if any, left to take place once you have confined the sample in the test tube.

You would need to use acids with a pH similar to that of the suggested acids for this method to work.

If you have adjusted the pH of the HCl already to match that of the suggested acids, then I suggest you check your thermometer to see if it is working properly. Can you warm it with you hand and get a change in indicated temperature?

Also, I just noticed you indicated you placed your steel wool sample "into a test tube filled with HCl acid". This is not how the procedure is described in the experiment. The mass of the HCl is likely enough to absorb all the heat from this reaction, therefore causing no measurable increase in temperature. Do follow the experimental procedure as written.

Once you adjust the pH of the HCl solution, and follow the procedure, you should get reasonable results.

Have fun!

I think Ed has probably fixed your problem, but I have one more caution: be sure you are using plain steel wool. Some steel wool comes loaded with cleaning powder that would interfere with the desired reaction. And some steel wool is made from stainless steel, which will probably react much less strongly to acids. As a last suggestion: use the finest grade of steel wool you can find, since the reactivity will be higher for finer grades of steel wool. (Hardware stores will carry a range of steel wool grades.)

Hello. I have just attempted this project and have only received results of various temperatures from each liquid but no rusting effect on the steel wool which is highly noticeable. I have followed each step but only get a constant temperature through the whole 15min. Anyone have any ideas?