How would you determine which layer is the aqueous layer?

To determine the aqueous layer - The NaHCO3 solution is an aqueous solution (water is the solvent). Water is more dense than ether and sinks to the bottom, while the ether sits on top. Most organic solvents will be less dense than water, unless you're working with halogenated solvents like methylene chloride, chloroform, or carbon tetrachloride.