Like Kevin and common sense, oil and water don’t mix. It is known. But why and how is that? They’re both liquids, so why don’t they just swirl together into a single liquid the way, say, grape juice and lemonade do? It’s all about miscibility (yes, that’s a real word), and in this Demo Science experiment, you’ll demonstrate to your students why oil and water don’t mix, then use the same principles learned there to create an even more impressive concoction. It’s science time!
For the first part of this experiment, you’ll need a quarter cup of water, a quarter cup of vegetable oil, some food coloring (any color will work; I prefer “bruise purple”), and a small, clear glass. Pour the water into the glass, then add several drops of food coloring and mix. Once your color is all nice and uniform, pour the oil into the glass. Unless you goofed something up super hard, the two liquids will remain in separate, well-defined layers.
Then, cover the glass with your hand (if your mitts are big enough) or a thick piece of plastic wrap. Keeping it tightly sealed, shake the glass so the oil and water get all sloshed around and mixed up. Set the glass down on a desk or table and observe. What happens?
Initially, there will be blobs or pockets of oil in the water and pockets or blobs of water in the oil. However, because of their immiscibility (i.e. they don’t/can’t mix), the two will slowly separate themselves and form two distinct layers again. Because vegetable oil is less dense than water, it will settle on top. Miscible magic!
Now for part two. Like The Empire Strikes Back, The Godfather Part II, and Staying Alive, this is the rare sequel that surpasses the original. For this one, you’ll need a quarter cup of honey, a quarter cup of liquid dishwashing soap, a quarter cup of water, a quarter cup of vegetable oil, a quarter cup of rubbing alcohol, two plastic cups (for mixing), two different food colorings (“bruise purple” and “jaundice yellow”, perhaps?), and a tall, narrow, clear glass.
Mix one of your food colorings with the water in one plastic cup; mix the other food coloring with the rubbing alcohol in the other cup.
This next part can get tricky, so be on your toes. Not literally on your toes, that would probably make it even harder. Just, y’know, watch what the F you’re doing. Start by pouring the honey straight into the center of the glass, being extra careful to not get any on the sides of the glass; if you do get honey on the sides, just go home for the day, because you ruined everything, ya big jerk! Fill the glass about a sixth of the way with honey.
Now, tip the glass slightly and pour your dish soap slowly down the side. Add roughly the same amount of soap as you did honey. This should make a nice two-layer liquid pileup. Good to go so far.
Each of the remaining liquids must be poured in very, very slowly so as to avoid beefing up the whole thing. They’re not as thick as the honey or dish soap, and might mix together if’n you’re not careful. So be careful, man!
Again, tip the glass slightly, then ssllloooowwwlllyy pour in the colored water, followed by the veggie oil and, finally, the rubbing alcohol. If you did it right, you should have five distinct layers of liquids in a single glass. As with a bear driving a car, your students may be wondering how can that be?
Miscibility & Viscosity & Density, Oh My!
As already mentioned, miscibility plays a big role. Another key factor is each liquid’s viscosity (“thickness,” to the layperson). Also at work: density—heavier liquids will, quite logically, settle to the bottom, while lighter liquids float atop the heavier ones.
With all this in mind, your students should have no problem sussing out why the different liquids were added to the glass in the order they were.