Question

A homogeneous solution is known to contain equal parts of diethyl ether and pentane. These liquids have similar boiling points and cannot be separated by fractional distillation. Devise a method for separating them.

Short answer

To separate diethyl ether and pentane, first add water to the mixture, allowing two layers to form. Collect the bottom water layer containing dissolved diethyl ether, then add anhydrous diethyl ether to extract the dissolved diethyl ether. Collect the top diethyl ether layer, dry it using anhydrous magnesium sulfate, and evaporate the solvent for purification. Finally, collect the top layer from the original mixture to obtain purified pentane. This method works by exploiting the different solubility properties of diethyl ether and pentane in water.

Step-by-step solution

Identify a solvent with different solubility for diethyl ether and pentane

In order to separate diethyl ether and pentane, we need to choose a solvent that has a different solubility for diethyl ether and pentane. Water is an appropriate solvent for this purpose because diethyl ether is partly soluble in water, whereas pentane is virtually insoluble in water.

Add water to the solution

Slowly add a known volume of water to the diethyl ether and pentane mixture. Allow the mixture to settle and observe the formation of two separate layers. The top layer will be diethyl ether and pentane while the bottom layer will be the water.

Collect the bottom water layer

Carefully collect the bottom water layer using a pipette or a separating funnel. Since the diethyl ether is partly soluble in water, this layer will contain some diethyl ether dissolved in it and no pentane.

Extract diethyl ether from the water layer

To extract the diethyl ether dissolved in the water layer, you can use an additional quantity of diethyl ether, for instance by adding a known volume of anhydrous diethyl ether to the collected water layer. The anhydrous diethyl ether will dissolve the diethyl ether present in the water layer, causing a liquid-liquid separation to take place. After allowing the layers to settle once more, the top layer will be the diethyl ether enriched with the extracted diethyl ether, while the bottom layer will be the water with a significantly reduced amount of dissolved diethyl ether.

Collect the top diethyl ether layer

Carefully collect the top diethyl ether layer using a pipette or a separating funnel. This layer will now have a higher concentration of diethyl ether compared to the initial mixture.

Dry and purify the diethyl ether

To obtain purified diethyl ether, dry the collected diethyl ether layer using anhydrous magnesium sulfate (MgSO4) or another suitable drying agent. After drying, filter the diethyl ether from the drying agent and evaporate the solvent to obtain the purified sample of diethyl ether.

Purify the remaining pentane

Finally, return to the original mixture and separate the remaining pentane from the initial diethyl ether layer. Since the pentane remains almost insoluble in water, you can collect the top layer as the purified pentane. It can be purified further by rotary evaporation or another evaporation method to remove residual diethyl ether. By following these steps, we have successfully separated diethyl ether and pentane using water as a selective solvent and made use of their different solubility properties.

Key concepts

Solvent Extraction

When faced with a mixture of diethyl ether and pentane that cannot be separated by traditional means like fractional distillation due to their similar boiling points, solvent extraction becomes a key expert move. This process involves choosing a second solvent that has different affinities for each component in the mixture. In our case, water is used as this second solvent, as it exhibits a significant solubility difference between the two liquids – pentane is insoluble while diethyl ether has partial solubility.

By adding water to the mixture, it serves to selectively dissolve diethyl ether. This results in two distinct layers due to their different densities, with the upper layer containing ethereal pentane and the lower water layer containing diethyl ether. Applying the principles of solvent extraction makes the process of separating these two organic compounds achievable and efficient.

Solubility Differences

The solubility differences between substances can be a powerful tool in separation techniques. In this scenario, we take advantage of the fact that diethyl ether is partially soluble in water, whereas pentane is not. This differential solubility is the crux of the separation method.

Understanding the solubility of different compounds in various solvents is fundamental in chemistry. In general, like dissolves like, meaning that polar compounds are soluble in polar solvents, while nonpolar compounds are soluble in nonpolar solvents. Water, a polar solvent, can interact with the slightly polar parts of diethyl ether but cannot effectively interact with nonpolar pentane, which explains why pentane remains separate.

Liquid-Liquid Separation

The principle of liquid-liquid separation is predicated on the concept that two immiscible liquids can be separated based on their density differences. In our approach to separate diethyl ether from pentane, the addition of water creates a biphasic system: one layer is the ethereal mixture, and the other is water.

This separation allows us to employ a separating funnel or a pipette to physically separate the two layers. The denser layer (water) settles at the bottom and can be removed to leave behind the less dense organic layer. This simple, yet effective technique showcases how liquid-liquid separation can be utilized to divide components of a mixture which are not evenly distributed between two immiscible liquids.

Purification Techniques

Once the initial separation of diethyl ether and pentane is achieved through liquid-liquid separation, the journey isn't quite over. The purification techniques employed in the subsequent steps are vital for achieving a high purity of the isolated substances.

For diethyl ether, an additional extraction step is used to decrease its concentration in the water layer, followed by drying with an anhydrous agent, such as magnesium sulfate, to remove any residual moisture. Filtration and careful evaporation free the diethyl ether from any remaining solvent.

As for pentane, it may be purified by additional methods such as rotary evaporation. These purification techniques are essential for removing impurities that could affect the properties or reactivity of the separated compounds, ensuring that scientists can rely on the purity of their samples for future applications.