Question

You have a solution of NaCl dissolved in water. Describe a method by which these two compounds could be separated.

Short answer

Heat the solution to evaporate the water and leave behind solid NaCl; use distillation to collect the evaporated water.

Step-by-step solution

Understand the Nature of the Compounds

NaCl (sodium chloride) is a salt that dissolves in water to form a homogeneous solution. To separate them, we need a method that allows us to exploit a property where they differ. Here, the key property we can use is the difference in their physical states when subjected to heat.

Apply Heat to the Solution

Heat the NaCl solution in a container. As the temperature increases, the water will begin to evaporate because it has a lower boiling point compared to NaCl. Continue heating until all the water has evaporated and only the NaCl remains as solid residue.

Collect the Evaporated Water

To preserve the water, you can set up a distillation apparatus. As the water evaporates, it is transferred to another container where it condenses back into liquid form. This is known as distillation which allows the collection of water separately from NaCl.

Collect the Solid NaCl

After all the water has evaporated, the NaCl will remain as a solid in the original container. This can be collected as pure solid NaCl, effectively separating it from the water.

Key concepts

Evaporation

Evaporation is a process we often see in our daily lives, such as when puddles dry up after a rain. In scientific terms, evaporation is the transformation of a liquid into a vapor at temperatures below its boiling point. It is a surface phenomenon, meaning that it occurs at the surface of the liquid.
For the exercise of separating sodium chloride (NaCl) and water, evaporation plays a crucial role. When the solution is heated, water begins to turn into vapor as it evaporates. This happens because water has a significantly lower boiling point compared to solid NaCl, which remains unchanged. The vapor then leaves behind the NaCl in its solid state.
This process is simple and effective for separating a solute from a solvent due to their differing boiling points.

Distillation

Distillation is a technique used to separate mixtures based on differences in boiling points. It involves heating a liquid to create vapor and then cooling that vapor to create a liquid once again, called the distillate. This method allows for the separation and collection of individual components from a solution.
In the context of the NaCl solution, once the water evaporates, distillation can be used to collect the water vapor. By condensing this vapor back into liquid, you recover the water in its liquid state while leaving behind the solid NaCl.
This makes distillation a highly effective method not only for separating NaCl from water but also for capturing and preserving both components in their pure forms.

Physical Properties

Physical properties refer to characteristics of a substance that can be observed or measured without changing its identity. These include properties like boiling point, melting point, density, and solubility.
In the NaCl and water separation exercise, we exploit the difference in their physical properties, namely their boiling points. Sodium chloride's high melting and boiling points mean it stays solid when the water evaporates. Water, having a much lower boiling point, turns into vapor first.
This difference in physical properties is key to successfully separating these compounds by evaporation and distillation.

Sodium Chloride Separation

Separating sodium chloride (NaCl) from water is a classic example of utilizing physical separation techniques. The process involves heating the solution to evaporate the water and leave solid NaCl behind.

• Start by heating the solution gently in an open container.
• Allow the water to evaporate completely, monitored by observing the disappearance of water.
• If the goal is to recover water, implement distillation to condense and collect it in a separate flask.
• The remaining content in the original container will be solid sodium chloride.

This method is efficient and based on simple physical principles related to temperature-driven state changes. It shows how understanding and leveraging physical properties can achieve effective separation of compounds in a mixture.