Salt is very important in our lives. Its chemical name is sodium chloride. It has been used for years as a preservative for food and for flavour. Salt is necessary for daily consumption, but only in very small amounts. Otherwise, it can cause blood pressure to rise. It is also added to icy roads to melt the ice, making the roads safe to drive on.
Due to its uses, a few methods have been developed to obtain it:
- Salt can be obtained from rocks by mining. Salt obtained this way is used on icy roads, so it does not need to be very pure.
- When salt is needed for food, it is purified. Water is sent down a hole underground and salt is dissolved in it. Then it is pumped to be purified and water is evaporated, leaving the salt crystals.
There is a danger that subsidence is caused by digging so many holes under the surface of the Earth, which means the ground may collapse. Therefore, great care is taken to leave spaces between the holes so there is enough rock to support the Earth's surface.
Alkalis are also important to us. When they are dissolved they give a solution with a pH higher than 7. They are used to make soap, glass, neutralising soil and dyes. Alkaline compounds react with acids to give salt and water. The LeBlanc Process was used for a few centuries to make alkali sodium carbonate. Sodium chloride was mixed with sulfuric acid and was then heated with limestone and charcoal. However, this process was extremely polluting, destroying the surrounding environment. Hydrogen chloride (an acid gas) was released as well as solid waste that released a toxic gas, hydrogen sulfide. The latter smells like rotten eggs. Later, hydrogen chloride was processed to form chlorine, which is used to kill microorganisms in water. This is called chlorination.
Brine is sodium chloride dissolved in water. An electric current can be used to separate brine into different substances, each having many uses. The diagram below shows this in more detail. Amongst the products is chlorine, which is a disinfectant and also used to make plastic. Additionally, sodium hydroxide is used to make paper and purify polluted water and hydrogen can be used as fuel that does not pollute the environment.