Question

For each of the following immiscible mixtures(A-D), which liquid is on top and which is on bottom (Upper or Lower part of test tube) and which part will the solid be dissolved in? Explain why.

A1: NaoH (aq)

A2: Methylene chloride

The solid is Salicylic acid

B1: Hexane

B2: Water

The solid is: Naphthalene

C1: Methylene chloride

C2: Water

The solid is: Fluorene

D1: Diethyl ether

D2: Water

The solid is: Triphenylmethanol

Answer 1

The more dense liquid will occupy the bottom of the separatory funnel while the less dense liquid will be at the top. Hence, we need to look at the densities of the liquids at room temperature (25⁰C). Density data are easily available in texts and internet sources.

A1: Since we have an aqueous solution of NaOH, we can assume the density of NaOH to be 0.997 g/mL.

A2: The density of methylene chloride is 1.33 g/mL.

Since methylene chloride is more dense than water, hence water will be at the top (lighter layer) while methylene chloride will be at the bottom.

Salicylic acid contains polar –COOH and –OH groups. Since water is a polar solvent and methylene chloride is less polar, salicylic acid will dissolve in the more polar NaOH solution.

B1: The density of hexane is 0.659 g/mL.

B2: The density of water is 0.997 g/mL.

Since hexane is less dense (light), hexane will be at the top while water will be at the bottom.

Napthalene is an aromatic hydrocarbon and hence non-polar. Hexane is a non-polar solvent while water is polar. Since like dissolves likes, hence, naphthalene will dissolve in hexane.

C1: The density of methylene chloride is 1.33 g/mL.

C2: The density of water is 0.997 g/mL.

Methylene chloride will be at the bottom and water will be at the top in a separatory funnel.

Fluorene is an aromatic hydrocarbon and hence non-polar. Methylene chloride is less polar than water and hence will dissolve fluorene.

D1: The density of diethyl ether is 0.706 g/mL.

D2: The density of water is 0.997 g/mL.

Water is denser (heavy) and hence will occupy the bottom of the separatory funnel. Diethyl ether, being less dense (light), will be at the top.

Triphenylmethanol contains a polar –OH group, but there are three phenyl rings as well which makes triphenylmethanol much less polar than normal methanol. Diethyl ether is less polar as compared to water and will dissolve triphenylmethanol.