Thursday, January 17, 2008

Redox Reaction Demonstrations

Lesson: Iron can take the form of two different ions in redox reactions
What Happened: Fe2+ + H2O2 → Fe3+ + H2O + O2
Ferrous iron + hydrogen peroxide → ferric iron + water + oxygen

Today we did some experiments from The Joy of Chemistry: The Amazing Science of Familiar Things (Demonstration 3, Stop-and-Go Chemistry, Page 73) which demonstrated reduction/oxidation, or redox, reactions. In reduction, electrons are gained, creating a negative ion. In oxidation, electrons lost (often involving oxygen), creating positive ions.

In preparation for this experiment, we first made up a batch of iron acetate, as instructed in the front of the book. Wearing Playtex gloves, John pinched off about a cubic inch of fine steel wool. We dropped it into a jar with 2 cups of vinegar and left it to soak for 24 hours. You could see bubbles of what the book says is hydrogen coming off the steel wool ball, which first floated on the top, then sank, then floated up again. (I did not try to ignite the hydrogen, although I thought about it.)

Ingredients for Iron Acetate

Then today, we gathered the following:

Safety goggles
Rubber gloves
Plastic bowls
Iron acetate solution
Household ammonia
Hydrogen peroxide

First we
ladled 2 tablespoons (30 ml) iron acetate into the bowl. Then we added 1 teaspoon of ammonia to make it turn red. But we found that the color was hardly noticeable. So we added a total of 5 teaspoons. You can see the difference below:

Left: 1 teaspoon ammonia. Right: 5 teaspoons ammonia

Next we dropped in 1 teaspoon (5 ml) of hydrogen peroxide, to turn the solution green. Just the one teaspoon was enough to make the solution the nice dark color.

Since we had set up two bowls (one for each boy) we were able to compare the color change.

Here is what iron acetate looks like chemically:

Fe3O(OAc)6(H2O)3]OAc (OAc is CH3CO2-)

Anthony helped me with this post. More redox experiments tomorrow!


Anonymous said...

Veeeeeeeeeerrrrrrrrrrryyyyy niiiiiiiiccccceeee j&c TC

Anonymous said...

You have your ferrous and Feric mixed up here, in order for the charges to balance you're reducing iron (III) to iron (II). The charges for the reduction of H2O2 won't work otherwise! Just so ya know!! :)

Anonymous said...

way to go!!!!!!!!!!!!!!!!!!!!111