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To separate a mixture of sand and common salt, which are two solid substances, three methods can be used, depending on:
- Physical characteristics , such as sieving the mix.
- Solubility , dissolving the salt.
- Melting point , melting the salt.
The simplest method to separate the two substances is that of solubility. That is, you can dissolve the salt in water, then pour the liquid into another container and finally evaporate the water to recover the salt. In this way, it is possible to easily separate the two components of the mixture, the sand and the salt.
Physical separation of salt and sand
This method consists of taking advantage of the density of each component to be able to separate them. Since both salt and sand are solids, and their size is visible to the human eye, the salt and sand particles could be separated using a magnifying glass and tweezers. However, this task is not practical at all, it would be very time consuming and almost impossible.
The best method of physical separation of salt and sand is based on the difference in density of one and the other. The density of salt is 2.16 grams per cubic centimeter, while the density of sand is 2.65 grams per cubic centimeter. This means that the sand is slightly heavier than the salt. Therefore, if a container of salt and sand is shaken, the salt will eventually be left on the surface.
This method is also used to search for gold, because this metal has a higher density than other substances and tends to settle at the bottom of a mixture.
Another way to use the physical separation method is through a sieve. By sifting the mixture of sand and salt with a very fine sieve, the small particles of the salt will pass through and the larger ones of the sand will not pass the sieve.
Separation of salt and sand by solubility
Another method of separating salt and sand is based on the solubility property of the components. A substance is said to be soluble when it can be dissolved in a solvent. Common salt or sodium chloride (NaCl) is a water soluble compound. On the other hand, sand, which is mainly silicon dioxide, does not have this property.
To implement this method it is necessary to perform the following steps. First, the mixture of salt and sand must be put in a pot or pan. Then a little water is added. To dissolve the salt more quickly we can heat the water. As the temperature increases, the solubility of the component also increases. Therefore, salt dissolves faster in hot water than in cold water.
If the boiling point of the water is reached and there is still solid salt left, you can add a little more water and continue the process. Subsequently, the container is removed from the heat and allowed to cool until it can be handled. Finally, the salt water and sand are transferred to separate containers.
To decant the common salt, put the salty water back into the empty pan or pot and heat until it boils. The process is repeated until all the water evaporates and only the salt remains. To speed up the evaporation of the water, it is convenient to use a large and shallow pot or pan.
Another homemade way to separate the salt water and the sand is to pass the mixture through a coffee filter, where the sand will remain.
Separation of sand and salt by melting point
The third method of separating the sand-salt mixture is based on the melting points of these components. The melting point of salt is 801°C, while that of sand is 1710°C. This indicates that salt melts at a lower temperature than sand. Therefore, to separate both components, the mixture of salt and sand can be heated above 801 °C, without reaching 1710 °C. Once the salt is melted, it can be poured into a separate container. However, this separation method is not recommended because it is not easy and requires very high temperatures.
Bibliography
- Bea Sánchez, JL Formulation and preparation of mixtures . (2020). Spain. Synthesis.
- Timberlake, KC General Organic and Biological Chemistry. (2013). Spain. Peasron.
