Which of the following type of lime is manufactured by burning marble, white chalk, calcareous tufa, pure lime stone, sea shell and coral?
Try it first: pick an option, then read the explanation.
Understanding Lime Classification by Source
Lime is classified based on the purity of the limestone from which it is derived. The chemical composition of the raw material directly determines the properties of the final lime product. The key distinction is between limes produced from very pure sources and those produced from sources containing significant impurities like clay.
Detailed Analysis of the Options
B. Fat lime
This is the correct answer. Fat lime (also known as pure lime, rich lime, or white lime) is produced by calcining sources that are very high in calcium carbonate (CaCO₃), such as marble, white chalk, sea shells, and coral. It is characterized by its high purity (over 95% CaO). It is called "fat" because it undergoes vigorous slaking (reacting with water) and swells to 2 to 2.5 times its original volume.
A. Hydraulic lime
This is incorrect. Hydraulic lime is produced by burning limestone that contains a significant amount of clay (silica and alumina). These impurities give it the property of setting and hardening under water, hence the name "hydraulic."
C. Hydrated lime
This is incorrect. Hydrated lime is not a type of lime based on its source; it's a form of lime. It is the product obtained after adding a controlled amount of water to quicklime (fat or hydraulic) in a process called slaking. Its chemical formula is Ca(OH)₂.
D. Lump lime
This is incorrect. This term describes the physical form of quicklime as it comes from the kiln—in lumps—before it is crushed or slaked. It is not a chemical classification.
Summary: Fat Lime vs. Hydraulic Lime
| Property | Fat Lime | Hydraulic Lime |
|---|---|---|
| Source | Pure sources (marble, shells, etc.) | Limestone with clay impurities |
| Purity (% CaO) | > 95% | 70% - 90% |
| Slaking | Vigorous, rapid | Slow |
| Volume Increase | High (2 - 2.5 times) | Slight |
| Setting Action | Sets only in air (by absorbing CO₂) | Sets in air and under water |
| Primary Use | Plastering, whitewashing | Mortar for damp conditions, foundations |
Study Tips
- Pure Source = Fat Lime: If the question lists pure materials like shells, marble, or white chalk, the answer is always Fat Lime.
- Fat = Swells: Remember the name "fat" comes from the fact that it swells up significantly when water is added.
- Hydraulic = Water: Remember that "hydraulic" lime is the one that can set under water due to its clay impurities.