As you are cleaning out the shared refrigerator in the kitchen of your apartment at the end of the school year, you find an unlabeled, clear plastic container in the back, left there by one of your roommates. This container is half-filled with something that you notice has separated into two layers: the top one is a dark yellow color, the bottom layer is more greenish. You assume that this biphasic mixture has an aqueous layer and some type of organic layer.

Question

As you are cleaning out the shared refrigerator in the kitchen of your apartment at the end of the school year, you find an unlabeled, clear plastic container in the back, left there by one of your roommates. This container is half-filled with something that you notice has separated into two layers: the top one is a dark yellow color, the bottom layer is more greenish. You assume that this biphasic mixture has an aqueous layer and some type of organic layer.

Without tasting, smelling, or removing either layer from the container, how can you clearly determine which layer is the aqueous layer using just material found in a typical kitchen?

Answer 1

One possible way to determine which layer is the aqueous layer is by using the concept of density. The water density is higher than most organic liquids, so if we carefully add a small amount of an oil-based substance (such as vegetable oil) to the container, the oil will float on top of the less dense organic layer and sink into the more dense aqueous layer.

Here's how you can proceed:

1. Obtain a small amount of vegetable oil from your kitchen.
2. Using a dropper or a small spoon, carefully add a few drops or a small amount of the vegetable oil onto the surface of the liquid in the container.
3. Observe what happens to the oil droplets.

If the droplets of oil float on top of the dark yellow layer and do not sink, then it indicates that the dark yellow layer is the aqueous layer. This is because oil is less dense than water, and it would not be able to penetrate the water layer.

If, on the other hand, the droplets of oil immediately sink through the dark yellow layer and form a separate layer with the more greenish layer at the bottom, then it means that the greenish layer is the aqueous layer. This is because the oil would not be able to mix with the water and instead form a separate layer.

By observing whether the vegetable oil floats or sinks, you can indirectly determine which layer is the aqueous layer without directly interacting with or removing the layers from the container.