Separating a mixture of pebbles, sand, and salt involves a series of steps that leverage the different physical properties of each component, primarily their size and solubility in water. The process relies on dissolving the soluble component (salt) and then using physical separation methods like sieving and filtration to isolate the insoluble components (pebbles and sand), followed by evaporation to recover the dissolved component (salt).
Step-by-Step Separation Process
Here's a breakdown of the method used to separate this common mixture:
1. Dissolving the Salt and Initial Sieving
The first crucial step is to add water to the mixture.
- The salt being soluble in water, dissolves in water and forms an aqueous solution.
- The sand and pebbles are not soluble in water so they will remain in the water.
After adding sufficient water and stirring to ensure the salt is fully dissolved, the mixture is ready for the first separation.
The mixture solution is then passed through the sieve. A sieve with holes large enough for sand and water to pass through but small enough to retain pebbles is used.
- The aqueous solution and the sand will pass through the sieve and the pebbles will be separated out.
At the end of this step, you have successfully separated the pebbles, leaving you with a mixture of sand and saltwater.
2. Separating Sand from Saltwater
Now you have a mixture of sand (a solid) and saltwater (a liquid solution). To separate the sand from the saltwater, you can use filtration.
- What is Filtration? Filtration is a technique used to separate insoluble solids from liquids using a filter medium that allows the liquid to pass through but retains the solid.
- How to Perform: Pour the mixture of sand and saltwater through a filter paper placed in a funnel. The sand particles, being larger than the pores in the filter paper, will be trapped on the filter paper (this is called the residue), while the saltwater solution will pass through the filter paper and collect in a container below (this is called the filtrate).
After filtration, the sand is left behind on the filter paper and can be dried to recover it. You are now left with only the saltwater solution.
3. Separating Salt from Water
The final step is to separate the dissolved salt from the water. This is achieved through evaporation.
- What is Evaporation? Evaporation is the process where a liquid turns into a gas (vapor). Heating the saltwater accelerates this process.
- How to Perform: Pour the saltwater solution into an open container, such as an evaporating dish or a wide pan. Gently heat the container (using a Bunsen burner, hot plate, or even leaving it in the sun). The water will evaporate and turn into water vapor, leaving the solid salt behind in the container.
Once all the water has evaporated, the solid salt is recovered.
Summary of Separation Techniques
This table summarizes the process and the techniques used:
| Step | Mixture Composition | Technique Used | Resulting Separations | What is Recovered/Left Behind |
|---|---|---|---|---|
| 1. Add Water & Sieve | Pebbles, Sand, Salt | Dissolving & Sieving | Pebbles from Sand + Saltwater Solution | Pebbles (retained by sieve) |
| 2. Filter the Remaining Mixture | Sand + Saltwater Solution | Filtration | Sand from Saltwater Solution | Sand (on filter paper) |
| 3. Evaporate the Filtrate | Saltwater Solution | Evaporation | Water (evaporates) from Salt (solid residue) | Salt (left behind) |
By following these steps, each component—pebbles, sand, and salt—can be successfully separated and recovered from the original mixture based on their distinct physical properties.
