Question

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

Short answer

Use evaporation to remove water, leaving NaCl behind.

Step-by-step solution

Understand the Properties

NaCl (sodium chloride) is a salt that dissolves in water to form an aqueous solution. Water can be removed by heating, but we need a method to separate the NaCl from water without losing the salt.

Choose the Separation Method

Evaporation is a suitable method for separating NaCl from water. In this process, we will heat the solution to evaporate the water, leaving the NaCl behind. This takes advantage of water's ability to change to a vapor at boiling point, while NaCl remains solid.

Set Up for Evaporation

Place the NaCl solution in an appropriate container, such as an evaporating dish. Ensure that the container is heat-resistant to withstand the boiling point of water.

Heat the Solution

Gently heat the solution using a Bunsen burner or hot plate. Maintain the heat until most of the water has evaporated, taking care not to overheat and cause the salt to decompose.

Collect the NaCl

Once the water has evaporated, turn off the heat and allow the container to cool. The solid residue remaining in the dish is purified NaCl.

Key concepts

Evaporation

Evaporation is a key separation technique widely used in chemistry. It involves the transition of a liquid into vapor, leaving non-volatile substances behind. In the context of separating a salt from its solution—such as NaCl in water—evaporation serves to remove the water, thus isolating the solid salt.

During the evaporation process, heat is applied to the solution. This increases the kinetic energy of water molecules, allowing them to escape into the air as vapor.

• Heat source options include a Bunsen burner or a hot plate.
• Ensure gradual heating to prevent the loss of any salt or damage to your equipment.

Typically, the heating continues until the water is completely evaporated, leaving behind solid sodium chloride. This method efficiently separates substances due to their different phases under heat.

Aqueous Solutions

Aqueous solutions are crucial in chemistry, as many reactions and separations occur in this medium. An aqueous solution is a mixture where a substance dissolves in water, becoming a homogenous mixture. In our scenario, NaCl is the solute, and water is the solvent.

For separating compounds in aqueous solutions, understanding the interaction between solute and solvent is essential. The characteristics of the solute-solvent interaction help determine the separation technique.

• Solubility: NaCl dissolves readily in water due to its ionic bonds.
• Evaporation: As water evaporates, the separation of NaCl from the water occurs.

This process effectively harnesses differences in phase changes to isolate components in a mixture.

Properties of Substances

Understanding the properties of substances is vital for selecting an appropriate separation method. Different substances have unique properties that influence how they interact with solvents and how they can be separated.

In separating NaCl from water, the distinctive properties are:

• Boiling Point: Water has a lower boiling point (100°C) compared to NaCl, which has a much higher boiling point, making water suitable for evaporation.
• State Changes: At room temperature, water is a liquid, while NaCl is solid, aiding in their separation via evaporation.

When considering a separation technique, these properties allow us to leverage simple methods like evaporation to efficiently isolate the desired compound.