America was built with cement and steel. Maybe not as much today, but this is the time of year when we would see our steel cars rusted through from snow and salt on the roads. Let’s investigate this process a little more closely.
Materials:
Steel wool (any fineness)
Clear glasses
Cold tap water
3% Hydrogen peroxide
Salt
Baking soda
Measuring cup (½ cup – 100 mL)
Teaspoon
Scissors
Safety: Hydrogen peroxide may cause burns – especially on open wounds. Have an adult help when using this substance. The solid waste generated can go into the garbage can, while the liquid waste can go down the drain.
Experiment:
Cut the steel wool into at least 5 equal-sized pieces. Spread out the wool pieces a bit and add one to each of 5 glasses. Add ½ cup of water to each of the 1st and 2nd glasses. Add ½ cup of hydrogen peroxide to each of the 3rd, 4th, and 5th glasses. Add a teaspoon of salt to the 2nd and 4th glasses, and add a teaspoon of baking soda to the 5th glass. (See planning grid below.)
Stir the contents in each of the glasses and allow them to sit. After a couple of minutes, you will begin to see some changes. Swirl the solutions occasionally and observe.
What’s happening?
Steel wool is an alloy (a combination of metal and another element) of iron and carbon. Iron, or Fe, will easily corrode (rust) when exposed to oxygen and an electrolyte (water, salt, acid, etc.). Hydrogen peroxide (H2O2) is an excellent source of oxygen because it breaks down into water (H2O) and oxygen gas (O2). Given this, it seems easy to predict that the 4th glass should corrode the fastest because it has both the oxygen (from the hydrogen peroxide) and the salt. However, sodium bicarbonate is also a salt (it has positive and negative ions), and although we see that it will also rust the steel wool, it isn’t nearly as good at doing so. We find that the chloride (Cl– ion) will also enhance the rusting process as it will cause the surface of the steel to pit, giving an active surface on the iron for the reaction with oxygen to occur.
Extension:
One of the electrolytes mentioned was an acid. How will vinegar (a solution of acetic acid) compare? Muriatic acid (hydrochloric acid) is used by masons, and this has acid and chloride ion components. Will dry salt produce rust in the presence of atmospheric oxygen? What happens if you use deionized water instead of tap water, which has ions in it?
References:
To view past “ChemShorts for Kids” activities, go to:
https://chicagoacs.org/ChemShorts.
- PAUL BRANDT
Rusty chain image: pexels-mikebirdy-282004.jpg
