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Understanding the concept of dissolution is essential in separation techniques. Dissolution happens when a solute---in this case, table salt (\(\mathrm{NaCl}(s)\))---mixes with a solvent, such as water, to form a solution. During this process, the salt particles are surrounded by water molecules and break away from their solid structure.
The water molecules interact with the ions in \(\mathrm{NaCl}\), separating them and creating a uniform mixture. This step is crucial in our salt-and-sand separation exercise. Table salt readily dissolves in water, whereas sand does not. As a result, when we add water to the mixture and stir, only the salt dissolves.
By dissolving the salt, we change its physical state from solid to aqueous, making it possible to later separate it from the sand. Remember:

• Salt is soluble in water, while sand is not.
• A solution is formed when salt is fully dissolved.

This method harnesses differences in solubility to achieve separation.

After dissolution, filtration is the next step, which allows us to separate the salt solution from the sand. Filtration is based on the principle that liquids and solids have different properties. A filter paper is used, acting as a barrier that lets the liquid (water with dissolved salt) pass through while retaining solid particles (sand).
We take the saltwater-sand mixture and pour it through the funnel equipped with filter paper. As gravity pulls the liquid through the paper, the sand gets trapped, and clear saltwater flows into the container below. This leaves us with:

• Sand residue on the filter paper, as it can't pass through.
• A clear liquid that contains the dissolved salt.

Filtration takes advantage of size difference between sand grains and salt solution molecules to effectively separate the components.

The final stage in the separation of salt from water is evaporation. Evaporation is a process that changes a substance from liquid to gas. In the case of our salt solution, we apply heat to evaporate the water and retrieve the salt.
Heating the saltwater solution causes water molecules to gain energy and escape into the air as vapor, leaving the salt behind. This transformation helps recover the table salt as solid crystalline forms on the surface of the container.

• When water turns into vapour, the salt is left behind.
• Salt crystallizes as the water content decreases.

This method exploits the difference in boiling points between water (100°C) and salt (very high), allowing one to turn to gas while the other remains solid. Through evaporation, we efficiently obtain dry salt after it's separated from sand and dissolved in water.