Science Buddies: "Ask an Expert"

PLEASE HELP!!!!! For my project I will have 3 Petri dishes, and I am testing if Ferro Fluid can effectively remove oil from water. Would it be effective if I tested oil in different types of water like salt, fresh, or muddy water? if not should I test it with different types of oil.

THANK YOU

Either is a decent variable, so I'll go through the pros and cons of each.

Salt water, fresh water, muddy water has the virtue of being inexpensive, but the difficulty is controlling the amount of salt or mud in the water. If you live near the ocean, you can pretty reliably get a concentration of salt water that is repeatable, if you're trying to do it by dissolving salt into water, it is more difficult. Mud you will pretty much have to dissolve a sample amount of dirt into the water, and "mud" is a very fuzzy term, in some places it has lots of plant matter in others it's more clay/sand, etc.

Using multiple types of oil has the virtue of tightly controlling the variable, but will be a little more expensive. Unfortunately, the most common type of real world oil spill involves "crude" oil, unrefined, and that is not something you can just buy on the open market. If you use automobile oil, you can get oil in different "weights" (10W30, 20w50) fairly easily, and the chemical composition of auto oil has very good standardization.

Because of the difficulty of controlling the "type of water" I would recommend using different types of oil, and in particular different types of automobile oil, where the type of oil very precisely measures the chemical composition.