Difference Between Gypsum and Lime

Chemistry is a subject that revolves around our lives. Calcium is the main component and is available in different forms. The forms vary from Bicarbonate, Carbonate to Hydroxide and Peroxide. Often people confuse gypsum with lime but they differ in a lot of ways and usage is also different for different products. 

Gypsum vs Lime 

The main difference between gypsum and lime is in the component that is added to calcium for making it. Gypsum is the sulphate salt of Calcium and is used in building, and as a hardening component whereas Lime is the carbonate salt of Calcium and is used in chalks and other such substances. 

Gypsum vs Lime

Gypsum is the sulphate salt of Calcium. Gypsum is made when the water surrounding sulphur evaporates and it comes into contact with oxygen. This results in the formation of sulphate that comes in contact with Calcium and further with water to form calcium sulphate dihydrate. Gypsum is a hard powdery substance that loses water to form the Plaster of Paris. 

Lime is another substance that is a salt of Calcium. The salt is acidic because of the presence of carbonate in it. The formation of lime is due to the perception of the aragonite or calcite that contains dissolved calcium and is either biological or non-biological. Calcium oxide controls the solubility of calcium carbonate. 

Comparison Table Between Gypsum and Lime

Parameters of ComparisonGypsumLime
DefinitionGypsum is calcium sulphate salt that is hydrated. Lime is formed due to the sedimentary rocks that are made up of dead marine animals. 
SolubilityGypsum is soluble in water due to the presence of Sulphate. Lime is insoluble in water and sediments due to the presence of carbonate in the salt. 
AcidityGypsum is neutral salt and the pH is around 7.Lime is an acidic salt because the acidic part of the salt is a strong acid. 
Affect on pHGypsum due to being a  neutral salt cannot change the pH of the soil. Lime can change the pH of the soil due to having an acidic group. 
CrystalsIn the process of crystallisation of gypsum, it can grow into larger crystals. Lime does not grow into larger crystals. 

What is Gypsum? 

Gypsum is commonly a Calcium salt and contains sulphate and is known as hydrated calcium sulphate due to the presence of two molecules of water. The chemical formula of gypsum is CaSO4.2H2O. The formation of gypsum is due to the action of oxygen on the rocks. 

The water in the rocks evaporates and a layer of sulphur is visible. The layer of sulphur combines with the oxygen of the air to form sulphates that attract the elements like Calcium and Magnesium. The Calcium is in the free form and the sulphate gets attached to it to form Calcium Sulphate and gains water to form gypsum. 

Gypsum has a variety of processes from which it is made. The natural process differs from the industrial process but it is a useful component. For the industry, it is used to make Plaster of Paris that is a powdery substance used for a variety of reasons due to its property of becoming hard after drying. It is formed when Gypsum is heated at a particular temperature and pressure and loses one and a half molecules of water. 

Gypsum is a soluble salt due to the presence of a sulphate group. It is also neutral and does not increase the pH of the soil if added in limited quantities. The salt is neutral because both the acid and base of the elements from where they are obtained are strong. 

What is Lime? 

Lime is yet another salt of Calcium that has a different acidic group attached to it. The group that is attached is Carbonate and the chemical name of lime is Calcium Carbonate. The chemical formula is CaCO3. The formation of lime is due to the sedimentation process. 

The formation of lime is generally underwater due to the formation of sedimentary rock. The sedimentary rock is formed by the dead plants and animals in the ocean along with the pressure and the action of salty water. Calcite or aragonite is formed that contains dissolved Calcium and are either biological or non-biological. 

The solubility of the salt is quite less in water due to the presence of the carbonate group. The solubility of this salt is also determined by the presence of Calcium Oxide that controls this. Calcium Carbonate in the industry is formed by the action of carbon dioxide on calcium oxide and the excess water is evaporated. On access passing of carbon dioxide Calcium bicarbonate forms that is soluble in water. 

The salt is acidic because it is formed by a weak base and a strong acid. It can also change the pH of the soil too acid and can cause harm to the plants as well as the animals living underneath. 

Main Differences Between Gypsum and Lime

  1. The hydrated calcium sulphate or gypsum has the chemical formula as CaSO4 whereas the sedimented rock at the bottom of the ocean formed due to dead marine life is known as Lime.
  2. Sulphate dissolves in water easily due to the formation of acid and therefore gypsum is soluble. In comparison to this, the presence of carbonate controls the solubility of lime in water and also is in conjugation with Calcium Oxide.
  3. Gypsum proves to be a neutral salt due to being a mixture of strong acid and base whereas Lime is said to have acidic properties because of the presence of a strong acid and weak bas
  4. When gypsum is added to the soil it does not change the pH whereas lime is harmful to the soil and causes decay to the plants due to being acidic
  5. Gypsum forms large crystals and is used in a variety of experiments in chemistry whereas lime does not crystallize but is a very important salt used for testing formation of carbon dioxide.

Conclusion

Gypsum and lime both are very useful salts present in nature and their process of making is different. Gypsum is the sulphate whereas lime is the carbonate salt of Calcium. Gypsum is formed due to the action of oxygen on the sulphur that is exposed due to the evaporation of water whereas lime is formed due to the action of water on the sediments of dead marine plants and animals. Gypsum is soluble in water and the solubility of lime is based upon Calcium Oxide and is also very less. Gypsum is neutral whereas lime is acidic and changes the pH of soil. 

References

  1. https://acsess.onlinelibrary.wiley.com/doi/abs/10.2136/sssaj1980.03615995004400010010x
  2. https://ceramics.onlinelibrary.wiley.com/doi/abs/10.1111/j.1151-2916.1987.tb05682.x
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